Rant: Is it too much to ask for a fuel gauge that actually works? - Page 1
Forum section: electronics / general

author: fubar.gr
author_rank: Unknown
timestamp: September 26, 2016, 04:39:06 pm
content: My main occupation is gas station attendant.What I've realised throughout the years of working there, is that fuel gauges on most cars don't work for shit.Sometimes I'll fill a tank to the brim, and yet the gauge will indicate less than full.This is the "easy" case, because I can easily demonstrate to the customer that the tank is full by adding some more fuel. The extra fuel will back up and overflow.The worst case is when the customer asks for a small quantity of fuel, like 5 or 10 liters, and the fuel gauge won't move at all. The customer will think (and rightly so) that I am ripping him off. But I am not, and have no way to prove myself.These events don't occur too often, maybe once or twice a month. But they can result in lost business, bad faith and lots of pointless arguing.Why does this happen? How does a car fuel gauge work and why do they occasionally glitch?

author: meeder
author_rank: Regular Contributor
timestamp: September 26, 2016, 04:42:11 pm
content: It's a simple float which is hinged to a potentiometer.The problem arises because fuel tanks are very complex in their shape in modern cars so the simple level measurement they do is not the most accurate way in determining the volume.Verstuurd vanaf mijn ZTE A2017G met Tapatalk

author: nctnico
author_rank: Super Contributor
timestamp: September 26, 2016, 04:49:26 pm
content: I'd have my gas pumps calibrated by a certified company. That should end any discussion with the customer.

author: Jeroen3
author_rank: Super Contributor
timestamp: September 26, 2016, 05:35:45 pm
content: The fuel indicator is a very very slow average, since driving makes an floater meter inaccurate. Today it's combined digitally with the flow meter to calculate remaining fuel. Adding 10 liters is like driving down a hill. Won't have any effect until you've parked for 15 min.You can test it by parking on a hill. When starting the next morning it will tell you several hundred kilometers less range. When you're at the first traffic light, you've magically gained fuel and range!

author: aandrew
author_rank: Frequent Contributor
timestamp: September 26, 2016, 05:42:29 pm
content: I have a 2015 Passat TDI. It absolutely astounds me that they don't do basic effing linearization of the stupid fuel gauge!The first 50km and I'm at 3/4 tank. The next 800ish km and I'm at 1/4 tank. The last 150km gets me to zero.EVERYTHING in this car is by-wire; there's absolutely no reason whatsoever that the fuel tank sensor could not have been linearized so that I have a proper linear progression from full to zero over the consumption of the fuel!

author: tggzzz
author_rank: Super Contributor
timestamp: September 26, 2016, 06:12:26 pm
content: One one of my cars, back in the 80s, the fuel guage was calibrated in Roentgens/hour. It was a big improvement over not having a fuel gauge at all.

author: KJDS
author_rank: Super Contributor
timestamp: September 26, 2016, 06:25:26 pm
content: I have a 2005 Saab 9-3 with over 200,000 miles on it. If the fuel gauge were meant to read from 0 (empty) to 1 (full) then the needle actually points to -2. It makes no difference if I've just put 60 liters of fuel in there or done 600 miles since I last filled it, that's where the needle sits.

author: Twoflower
author_rank: Frequent Contributor
timestamp: September 26, 2016, 06:45:13 pm
content: I think the 10l-nothing happens is build in by design. To prevent up and downs from sloshing they prevent ups (and probably downs as well) unless there's a certain change of the level. Sometimes you could force a re-read if you trigger the check-system button.My 2000 Audi A4 2.0l had also a very non-linear behaviour. The first few km it told me a reach up to over 1000km (usually I got about 700km range) and the gauge not moving for about 100-200km. Then the normal linear range was very accurate (reach and gauge). Then usually the reach dropped from roughly 120km straight to 80km. This happened if the reserve range is reached and it staid there for about 30 to 40km.I expected that actually the other way round. I heard that there must be at least 80km reach if the fuel-warning lamp lit. Not the other way round 'don't show more than 80km reach if warning lamp on'From what I was told: The engine temperature is everything but the engine temperature. If it would be the correct actual temp, everyone would drive to the next garage and get the engine checked. But that could be an engineers bed time story.

author: PChi
author_rank: Frequent Contributor
timestamp: September 26, 2016, 06:48:26 pm
content: The early Ford Sierras had a fuel gauge marked in litres (I think) and it worked well. I also visited the factory where they had made the resistive sensor after it had closed. It must have cost a lttle more money than the cheap stuff usually used but wasn't a success because the idea didn't take off.They are back to the 1/4, 1/2, 3/4 and full marks. I drove a new Mini recently it just had a few LEDs. There wasn't a gauge!It's all about initial cost at acceptable quality.More expensive cars just have more stuff. The new car buyer doesn't seem to want to pay for better quality at a slightly higher price.The motoring press don't help and don't bother to look behind the dashboard.

author: nctnico
author_rank: Super Contributor
timestamp: September 26, 2016, 06:53:02 pm
content: Quote from: Twoflower on September 26, 2016, 06:45:13 pmIt is the temperature of the coolant which is kept somewhat constant using a thermostatic valve so the engine is in it's designed temperature range.

author: SeanB
author_rank: Super Contributor
timestamp: September 26, 2016, 07:08:49 pm
content: Quote from: DiligentMinds.com on September 26, 2016, 06:23:25 pmYou do not even have to do that with a VW. Simply buy the VAG adaptor ( bluetooth one is probably the easiest) and use your smart phone and the app. The tank sensor is pretty well linearised for the vehicle, and the resolution in there is to the litre. The non linearity is how the manufacturer programmed the instrument panel in how to display fuel quantity, so that a full tank is shown as full, and when it hits empty you have 80km left at average fuel consumption. There is also a lot of smoothing done there, to reduce the effect of cornering and acceleration on it.That VW sensor has a multitap resistor bank in it, with the wiper selecting discrete segments, which step at litre increments ideally, but can be a little out at the extremes. I know from changing the sensor ( plus the fuel pump, as they come as a complete unit) on my car. You can read fuel remaining off the instrument panel in litres, and as I was trying the sensor out of the tank I found it would respond on the bus immediately to the movement of the float, and that each segment was one half litre of tank capacity or so.The most common reason the fuel gauge does not move at all on modern cars is that the driver did not actually remove the ignition key. The instrument panel will keep the smoothing info so long as it has ignition or accessory power on, so the gauge will not move until the car has either sat with ignition on for 2 minutes, or the car has been driven for 2 minutes.

author: KJDS
author_rank: Super Contributor
timestamp: September 26, 2016, 07:10:23 pm
content: Quote from: nctnico on September 26, 2016, 06:53:02 pmA lot of them, if the coolant temp is roughly in the right range, then the gauge will be sat right in the middle and won't move until the coolant is either very cool or boiling away.

author: rdl
author_rank: Super Contributor
timestamp: September 26, 2016, 07:13:38 pm
content: Wee hours of the morning sometime in 1986, middle of nowhere Alabama. I'm with a friend and her aunt who's moving from Alabama back to Indiana. We volunteered to help her. We're near the end of the trip down from Indiana. I'm driving, it's the aunt's car, and it sputters and dies. Now what? I said, and looked toward the aunt.She leans over and looks at the instrument panel. "We might be out of gas"."But it shows almost a quarter tank?" I say.She sort of shrinks down a bit and says"Sorry. I should have told you. When it gets to a quarter tank, it's really almost empty."

author: SeanB
author_rank: Super Contributor
timestamp: September 26, 2016, 07:14:44 pm
content: Quote from: nctnico on September 26, 2016, 06:53:02 pmThat gauge is designed to sit in the middle of the range when the engine is within 10C of the thermostat opening temperature, ignoring the actual sensed temperature till it is either higher or lower, so the needle does not wander.There were a few older GM vehicles where that gauge was actually connected to 2 thermal switches, so that it really only had 3 positions it would take 5 minutes to go between, cool, normal and "thar she blows".

author: Red Squirrel
author_rank: Super Contributor
timestamp: September 26, 2016, 07:22:44 pm
content: Speaking of sketchy fuel indicators, I saw one designed for propane tanks at the store so figured I'd buy one as it could be handy. It's just a piece of plastic that clips on the tank, how is that even suppose to work? It clearly does not. lol.

author: meeder
author_rank: Regular Contributor
timestamp: September 26, 2016, 08:10:59 pm
content: This reminds me. The mk3 VW Golf and other cars from the same years which used the same Instrument cluster had a service mode which you could enter.One of the things it did was remove the filtering from both the temperature gauge and the fuel gauge.As a result the fuel gauge leaped up and down during normal driving.The temperature gauge is also filtered during normal operation. Between 70 and 100 degrees C it would sit still at 90 degrees without moving. In the service mode you could see it fluctuate during driving.Verstuurd vanaf mijn ZTE A2017G met Tapatalk

author: bitseeker
author_rank: Super Contributor
timestamp: September 26, 2016, 08:42:06 pm
content: Quote from: DiligentMinds.com on September 26, 2016, 05:28:18 pmOK, I'm game. How does one go about getting or making one? The sensor in one of our cars works fine until you put fuel in the tank. Then, the meter shows empty until you drive from a few to many miles, during which the needle slowly makes it way back up to the actual fuel level.

author: dmills
author_rank: Super Contributor
timestamp: September 26, 2016, 08:52:17 pm
content: Quote from: SeanB on September 26, 2016, 07:14:44 pmIIRC the guy who came up with that actually won an award for it.Regards, Dan.

author: rrinker
author_rank: Super Contributor
timestamp: September 26, 2016, 08:55:03 pm
content: Quote from: tggzzz on September 26, 2016, 06:12:26 pmSo, you were a sub driver, or was it a carrier?

author: rrinker
author_rank: Super Contributor
timestamp: September 26, 2016, 08:57:52 pm
content: Quote from: Red Squirrel on September 26, 2016, 07:22:44 pmIt's actually a thermometer of sorts. Sometimes they work. Better are grills where the tank sits on what is effectively a scale and the weight moves a pointer. Or just knock on the tank and you can get an idea of how full it is.

author: raptor1956
author_rank: Frequent Contributor
timestamp: September 26, 2016, 09:04:16 pm
content: Quote from: DiligentMinds.com on September 26, 2016, 05:28:18 pmNot just fighter jets -- most all AC to the best of my knowledge use capacitance probes for fuel quantity measurement. Actually, the design of the probes take into concideration the geometry of the tank so the plating on the probe varies with the shape of the tank. In addition, to account for differences in fuel dielectric and fuel density they also have a compensator (capacitor) that adjusts for fuel density and variations in the dielectric properties from batch to batch.Fuel is measured by mass not volume as the energy is related to mass not volume.For cars the typical idea is to display the fuel level but usually skew the display so as to indicate less fuel than the car actually has. It's not uncommon for a car to indicate zero fuel with 2 or more gallons of fuel remaining. And they tend to be non linear with the first half of the indication providing something like 55%-60% of actual fuel with the second half 40%-45%.Basically, they fool you into thinking you're getting great mileage and then, as the fuel level begins to drop more quickly in the second half, they trick you into stopping for gas early so you don't run out.Many modern cars monitor fuel use by calculating actual consumption (ie, fuel flow) from the fuel pressure, rpm and duty cycle of the injectors. These monitoring systems can be within 1% but may be as bad as 5% -- the one in my 2012 Ford Focus is a bit better than 1% over 64K miles.Brian

author: tggzzz
author_rank: Super Contributor
timestamp: September 26, 2016, 09:08:38 pm
content: Quote from: rrinker on September 26, 2016, 08:55:03 pmNeither 😀. Given that it was the cheapest meter I could find in a surplus shop in Cambridge, I presume it had been liberated from a physics lab.Memo to self: get a Geiger counter, go around a supermarket and point it at LoSalt, and see the staff's reaction.

author: bitseeker
author_rank: Super Contributor
timestamp: September 26, 2016, 09:42:29 pm
content: Quote from: tggzzz on September 26, 2016, 09:08:38 pmLOL!QuoteAnd post to YouTube.

author: Someone
author_rank: Super Contributor
timestamp: September 26, 2016, 11:28:40 pm
content: Quote from: SeanB on September 26, 2016, 07:14:44 pmI know my car has an accurate coolant temperature gauge, it matches the OBD data and does not have a dead zone or long lag to the filter. I can drive for 20 minutes on a very cold day and it will still be under 80, never been stuck in traffic bad enough to challenge the cooling system but I assume it would indicate over temperature accurately too.

author: calexanian
author_rank: Super Contributor
timestamp: September 27, 2016, 01:38:13 am
content: Here is a typical Fuel Sending UnitAnd here is a typical set of guts for the Potentiometers.Generally in older cars, pre OBD the fuel gauge in the dash has a movement that is thermal mechanical rather than purely electrical. This has a dampening effect on the needle so it is not bouncing around when the gas sloshes around in the tank. This system generally creates a non linearity in the movement of the needle. It also varies with ambient temperature. With modern electronic displays the intentionally make the needle more sensitive on the lower end so you get the hint to fill up. I you have a modern system that displays the actual volume of fuel remaining, i have found that they are accurate enough for most people. Of course we are not most people.

author: Brumby
author_rank: Unknown
timestamp: September 27, 2016, 02:04:09 am
content: Once when I did some work for a local mechanic, he gave me a car to look at with a faulty fuel gauge indication. After playing around with the sender and gauge, I found a resistor shunt (of around 1K, I think) would bring the scale reading to a reasonable match. He dismissed this idea and went looking for something else.A little while later he came back to me and asked to see how well it tracked - and after I showed him he told me to do it. Customer never complained or even commented on the result.From the relative closeness of the tracking between sender and gauge after fitting my 'bodge', I suspect there might have been a shunt resistor already designed into the circuit - but it had failed.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: September 27, 2016, 03:38:41 am
content: Quote from: calexanian on September 27, 2016, 01:38:13 amThat is a typical new condition picture. It is a tough environment. Immersed in a solvent that will disperse any lubricant. Constant jitter and wiggle from sloshing and road roughness superimposed on bending and twisting forces that go in all directions due to acceleration, braking and turning at various levels in the fuel tank. The picture doesn't show well but they tend to have multiple parallel wipers for redundancy. My experience is the resistive element holds up well. The failures occur either in the pivot, which wears until the wiper geometry is lost, or the fingers of the wipers all wearing down until they no longer consistently contact, usually having lost half or more of their length.For the OP - customers of the type that you describe would complain if you poured your gasoline into a graduated cylinder in front of them before putting it in the tank. If the in car gauge was relatively accurate they would natter you about the 32 milliliters that you didn't deliver (according to their gauge). Just be thankful you don't have more of them.

author: Cubdriver
author_rank: Unknown
timestamp: September 27, 2016, 04:18:32 am
content: Quote from: Red Squirrel on September 26, 2016, 07:22:44 pmIs it a liquid crystal thermometer? I recall seeing those in the past; they were adhesive strips that were applied to the side of the tank. To use it, you poured warm (IIRC) water over it. The idea was that the part covering the empty tank would heat more than that over the bottom containing the liquid, which would act as a heat sink and keep that section cool. The 'hot' part would change color, and you could then read the propane level based on the color boundary.-Pat

author: calexanian
author_rank: Super Contributor
timestamp: September 27, 2016, 05:28:34 am
content: Quote from: Brumby on September 27, 2016, 02:04:09 amIt probably had the wrong range resistance sender in it. Very common. All of them have series supply resistors to prevent any spark from occurring for obvious reasons. there are some impedance matching boxes out there that will translate from one resistance range standard to another for mixing and matching senders to gauges.

author: tszaboo
author_rank: Super Contributor
timestamp: September 27, 2016, 10:37:25 am
content: IDK, mine is preatty accurate, from what I've seen. 10 bars, digital. I drive ~100 Km, ~4 liter of petrol disappears, a ~bar disappears. When the last one is there, car beeps, I have a 3-4 liter left, time to go to the station.

author: Brumby
author_rank: Unknown
timestamp: September 27, 2016, 11:25:01 am
content: Quote from: calexanian on September 27, 2016, 05:28:34 amI doubt it.This was in a car that was several years old - and had obviously been working properly until recently at that time.I am very familiar with various sender resistance ranges, having done numerous LPG conversions - many of which had senders with resistance ranges matched to the vehicle's fuel gauge.

author: Psi
author_rank: Super Contributor
timestamp: September 27, 2016, 12:18:27 pm
content: I noticed my fuel gauge worked much better after adding one of those fuel system cleaning additives to the tank.Before then the gauge seemed to drop from full to half after using only 10% of the fuel. Where as after using the additive it seemed to be more like 30-40%My assumption was that the additive cleaned the built up of dirty/residue off the potentiometer contact strip.

author: fubar.gr
author_rank: Unknown
timestamp: September 27, 2016, 01:05:13 pm
content: Quote from: CatalinaWOW on September 27, 2016, 03:38:41 amI've actually done something similar. After a customer complained, I brought forth my graduated flask that looks exactly like this, (only mine is in liters)This can detect a 0.1% difference in volume, where + or - 0.4% is within the legal limits.I filled it with 5.00 liters from the pump in front of the customer and it was spot on. The customer wasn't persuaded.In my experience, when the customer thinks you have ripped them off, their brain's logic circuitry shuts off and there's absolutely no way to convince them otherwise.Quote from: nctnico on September 26, 2016, 04:49:26 pmMy pumps are tested regularly by 4 different bodies.1) On a yearly basis by one government agency2) On an almost monthly basis by another government agency. These guys also test for fuel quality.3) By the company that supplies me with fuel4) A third-party lab, commissioned by my fuel supplierAll these certificates don't amount to anything to an irate customer.

author: vk6zgo
author_rank: Super Contributor
timestamp: September 27, 2016, 11:58:57 pm
content: Back in the day, (1960s & earlier),when you filled your tank,the gauge went straight to "full".This nice,fast response would have caused problems with fuel slopping around whilst driving,so tanks were fitted with internal baffles.The "bean counters" of the 1970s didn't like the baffles,as they added to the cost of manufacture,so they were removed.This required a gauge which had a very slow response,so as to avoid rapid changes in readings during driving.I suspected at the time that the meters used were thermally based to give the required slow response,but I never pulled one apart.Whole generations have been brought up on the notion that,if you fill your tank,the fuel gauge will not show "full" till you are a couple of km down the road.

author: Brumby
author_rank: Unknown
timestamp: September 28, 2016, 12:20:38 am
content: Quote from: vk6zgo on September 27, 2016, 11:58:57 pmYes, indeed.

author: calexanian
author_rank: Super Contributor
timestamp: September 28, 2016, 02:37:59 am
content: Quote from: Brumby on September 28, 2016, 12:20:38 amThats because of the thermal lag in old style gauges. Takes a while to stabilize.

author: Brumby
author_rank: Unknown
timestamp: September 28, 2016, 02:48:29 am
content: Quote from: calexanian on September 28, 2016, 02:37:59 amA few understood the principle - but most understood the fact.In practice, nobody really found it a problem once they got used to it.... At least in my experience.

author: Keicar
author_rank: Regular Contributor
timestamp: September 28, 2016, 04:53:42 am
content: Yep, I remember as a child taking apart the gauge cluster of a Honda Scamp- the fuel gauge was based on a little heating element that warmed up a bimetallic strip, as I recall.

author: Berni
author_rank: Super Contributor
timestamp: September 28, 2016, 05:23:50 am
content: You should see fuel gauges for LPG (Its propane/butane for those that never heard of it) then.My car is modified to also run on LPG (about half the price of gassoline here) It only has 5 LEDs to show the fuel level but with how well it shows they might as well just be blinking randomly. When you start the car it shows one thing and after a bit of driving it changes its mind etc. Only thing that seams to be reliable is that when you get on the last LED you got about 100km left in the tank. For this reason i reset my trip counter when filling up, that way i know how much i have left by knowing how far i typically get on a full tank.Only certain gas stations have LPG and since i also keep about 100km worth of gasoline in the tank i tend to run it down very close to empty on LPG.

author: Brumby
author_rank: Unknown
timestamp: September 28, 2016, 05:53:16 am
content: It depends on the LPG installation as to what happens with LPG fuel level indication. There are two basic options - one is to have a separate LED display (which is what I have in my car) and, yes, it is not particularly precise. The other is to have the sender integrated into the vehicle's normal fuel gauge, switching between the petrol and LPG sensors as you switch fuels.The fuel level detection inside an LPG tank is done through magnetic coupling. A brass plate is mounted on the tank, with the float inside connected to a magnet, which is rotated according to the fuel level. On the outside of the brass plate is the sender unit - basically a variable resistor where the wiper position follows the magnet's orientation.The sender design is a generic one, with a PCB having several pads for SMD resistors and this can be configured for whatever resistance range is required - both ascending (0-90 ohm) and descending (110-4 ohm). I have a close-up photo of one somewhere....

author: rs20
author_rank: Super Contributor
timestamp: September 28, 2016, 06:09:18 am
content: Quote from: Red Squirrel on September 26, 2016, 07:22:44 pmAs the liquid in the tank evaporates (to replace the gas drawn from the top of the tank), it cools down. Hence, there is a zone of coldness from the level of the liquid, down. The "fuel indicator" is simply, a colour-changing plastic that reveals this cool zone, hence where the liquid level is inside the tank. Obviously requires good thermal contact, and it only works (if ever) when the tank is in use (i.e., you'd check it after your BBQ, not before.) Slightly dodgy, yes, but it absolutely does work at leastsometimes.

author: Jeroen3
author_rank: Super Contributor
timestamp: September 28, 2016, 07:16:34 am
content: Today there are also bi-fuel cars. And apparently the way to know LPG is run out is by seeing liquid fuel consumption skyrocket. If you want to drive economically with those you'll be filling every 200 km (twice a week). Only benefit seems tax evasion. Would not recommend.

author: Brutte
author_rank: Frequent Contributor
timestamp: September 28, 2016, 07:59:49 am
content: For me the fuel tank gauge information is interesting only when the fuel goes low.And it is critical not to go lower than zero (been there, done that).So if I had a choice, a practical gauge should be tailored for low levelsonly.The information "1250km range left " and 250km range left " has equal values for me (no value). However 250km and 50km respectively changes everything. Of course I'd prefer to visit the gas station when the range has just fallen below that 50km, with a range of 1200km, instead of 800km that I am doing now with my inaccurate gauge.

author: Berni
author_rank: Super Contributor
timestamp: September 28, 2016, 08:35:56 am
content: With the 47 liter LPG tank i can make up to about 480km so it does make sense to do it. Gasoline is not cheap in Europe.With these aftermarket conversions you do clearly know when it has run out as it makes a loud beep and looses power for a fraction of a second as it switches back to gasoline. After it says its empty you can also squeeze a few extra km out of it by turning it back on and being very easy on the throttle so that the pressure does not drop bellow its cutoff point.Oh and another trick i was using on my former regular diesel car is that i kept watching the km left in the trip computer rather than the fuel gauge. That thing would peg on zero when there was still like 150km left in it, but the trip computer had a pretty reliable display that counted down in 1km resolution. I don't know how much you still have when that says 0 since running a diesel dry is usually a bad idea. While on my new car the trip computer rounds the km remaining to 10km and constantly changes its mind by up and down by 30km.Don't worry when cars eventually go electric we will have better fuel gauges since we figured out lithium battery charge monitors pretty well.

author: rrinker
author_rank: Super Contributor
timestamp: September 28, 2016, 02:57:02 pm
content: With most any relatively modern gas car it's also a very bad idea to run the tank down to the last bits of fuel. The fuel pump is almost always now located in the fuel tank, cooled by the liquid surrounding it. You might get away with it once or twice, but running it down constantly will result in a failed fuel pump and an expensive repair since in a lot of cars it is VERY difficult to get to. When the low fuel light comes on in my car, it universally takes only about 10 gallons to fill up - it has a 14 gallon total tank capacity according to the specs.

author: BradC
author_rank: Super Contributor
timestamp: September 28, 2016, 03:31:26 pm
content: Quote from: rrinker on September 28, 2016, 02:57:02 pmActually they are cooled and lubricated by the liquid passing through them. The issue with low fuel levels appears to be less about surrounding cooling and more about the change between a positive and negative pressure at the pump input. Once the fuel level falls below the impeller the pump is more prone to cavitation. This is all subject to pump type too. The other cooling related issue is with a smaller total liquid volume in the system, you reject more heat per volume into the fuel as it passes through the engine bay, and the fuel heats up more as there is less volume to dissipate the heat through the tank walls.Again, a different issue with newer non-return injection systems, but my meandering point is it's not really about pump cooling as much as a load of contributing factors.

author: Twoflower
author_rank: Frequent Contributor
timestamp: September 28, 2016, 05:40:54 pm
content: Quote from: SeanB on September 26, 2016, 07:14:44 pmYes that actually matches my observations: Riding on the German Autobahn @180km/h and then reaching the end of a traffic jam (breaking early enough!) the temperature seemed not to change a bit from 'right in the middle'. So I don't think the engine temperature was that stable.

author: SeanB
author_rank: Super Contributor
timestamp: September 28, 2016, 07:27:36 pm
content: Sat in my VW and had it plugged in and mapping, you could tell fuel level was sloshing around in the tank ,and battery voltage changing with RPM and engine temperature, and that the indicated temp does not agree much with the actual sensed coolant temperature.

author: rrinker
author_rank: Super Contributor
timestamp: September 28, 2016, 09:42:48 pm
content: I have to do that in my car, there is a crazy code sequence you can key in (partly involving some digits from the VIN) that unlocks stuff like the actual speed (unfortunately for me, only available in kph), water temp (the dash gauge on my car is oil temp), and all kinds of other neat info. Sadly it does not stay active through a shutdown, and it's not easy to memorize. My oil temp gauge seems to gradually creep up from cold start, but then it never goes past the mid point if I am driving fast in the open or stuck in bumper to bumper traffic - though I HAVE seen it DROP on a cool day while cruising at speed (lots of air flow over the radiator, and the oil to water oil cooler). Seems like the low to mid point is somewhat representative of actual, and it will only go over mid if there is a problem.You know it's fake when an oil pressure gauge doesn't vary one bit with engine RPM. My truck seems legit, at idle it drops and as the engine RPM increases the pressure goes up. It also has a voltmeter, but only very gross graduations, and it seems to just go to oen point and stick there regardless of lighting load and engine speed. There's a small red area at the low end, a large green area (no actual voltages marked, it takes about half the range) and a small red area at the top. I'm guessing simple window comparator type of thing and not a real voltmeter.

author: Berni
author_rank: Super Contributor
timestamp: September 29, 2016, 05:22:19 am
content: Well if you look from the perspective of a average car driver this is sort of what they want to have. They want there dash to say "everythyng is ok" or "go see a mechanic".You see the same trend with the microsoft windows bluescreen. They used to barf all sorts of information at you. Most of it was genuinely useless unless you ware someone working on the bowels of the OS or writing a driver, but a few parts are useful for tracking down your problem. In windows 10 all it does is tell you in text that something went horribly wrong and tells you to type something in to google like for example "MEMORY_ACCESS_EXCEPTION". You can still look at the full log after you reboot, but for most windows users this bluescreen is what they want since it simply tells them "Your computer is screwed so go get your son/nephew to fix it or google this if you want to have a go at it"All the info in the car is still there sitting on the OBD port, but the average user gets presented with the short summary of the most important information. Still annoys us engineering types that want to see what is going on.

author: wraper
author_rank: Unknown
timestamp: September 29, 2016, 05:25:40 am
content: Quote from: Berni on September 29, 2016, 05:22:19 amOnly if it was actually saved.

author: Brumby
author_rank: Unknown
timestamp: September 29, 2016, 05:35:38 am
content: Quote from: wraper on September 29, 2016, 05:25:40 amDetails... Details...

author: Cubdriver
author_rank: Unknown
timestamp: September 29, 2016, 08:10:50 am
content: My understanding is that a lot of modern auto temperature gauges have a flattened response curve with a plateau in the vicinity of normal operating temperature. I dug into it years ago when I noticed that the temp gauge in my Miata was rock steady at center scale once the car warmed up, and never visibly varied whether it was the dead of winter or the hottest day of summer. What I found was that the sender has NTC and PTC elements in it, and they're selected so that one has a smaller range centered around 'normal' operating temp. It winds up changing its resistance in the opposite direction to the main one in that temp range, resulting in a flat spot in the resistance curve in that makes the gauge read a steady value even though the temp is varying. Basically, if you see it start to rise above normal, you can bet something is definitely amiss.I don't like it, and would much rather see the actual variations, but as someone mentioned above, most people just want go-no go information and couldn't be bothered learning anything about what's actually happening.It seems we're definitely in the minority here wanting to be able to actually monitor the systems we deal with.-Pat

author: Berni
author_rank: Super Contributor
timestamp: September 29, 2016, 08:43:54 am
content: There is also a dash gauge crime in my dads modern Volvo. Its a automatic so it has a bar of square white LEDs on one side to tell you what state the transmission is in. On the other side of the all digital LCD dash they put a fuel gauge in the same style. So as a result your fuel is shown by a bar of i think 8 LEDs. So as you get towards the end of your tank you have just 1 LED lit...so do i have like one full LED (1/8th the full tank) is is that LED a tank with a few drops left in it that was rounded up to 1?

author: tszaboo
author_rank: Super Contributor
timestamp: September 29, 2016, 09:26:03 am
content: Quote from: Jeroen3 on September 28, 2016, 07:16:34 amWhat??? You realize, LPG is being sold at gas stations in many countries? At least they dont run on that dirty-dirty diesel that this part of the world loves soo much (btw, I'm all in for increasing the tax on diesel by 300%. Stupid goverments.)

author: kaz911
author_rank: Super Contributor
timestamp: September 29, 2016, 10:02:45 am
content: And how about getting Km/h or mph gauges to show right data? I have not been in a car for a long time where they wore even CLOSE to being right. Mostly 5-10 km/h off at 100 km/h - and of course always to the side that make you go slower. Some cars I have driven it was even worse (Factory wheels, right pressure) - up to 17 km/h was the worst I tried so far. All cars with < 5000 km on them.VW - usually around 5-8 km/h off more towards 8 than 5Mercedes - 3-5 km/h off - so far the most right on averagePorsche 3-7 km/h offOpel - 5-12 km/h offAnd the Renault was the winner with 17 km/h wrong indication at 100 km/h - but that was a Renault Kangoo(roo) so I guess it jumped more than it drove.I don't own a car - and rent a lot at the moment... with the big variation - no wonder you get people in the overtaking lane doing 85 as they think they are doing 100...Not once have the indicator shown too little - so it is a safety feature - but they could at least agree on a -2 or -3% max fault indication...

author: Jeroen3
author_rank: Super Contributor
timestamp: September 29, 2016, 10:13:12 am
content: Quote from: NANDBlog on September 29, 2016, 09:26:03 amThe ownership tax of these hybrid and bifuel cars is much lower.Owning diesel is already twice as expensive. Average people won't buy diesel here.Full electric cars are almost free.

author: JPortici
author_rank: Super Contributor
timestamp: September 29, 2016, 10:41:41 am
content: Quote from: NANDBlog on September 29, 2016, 09:26:03 ami think he meant reduction... don't know if it's still going on but you had a loooot of subsidies with methane/gpl/dual fuel cars here some four years ago.(don't really care, all cars converted to dual fuel i've seen were god awful. trunk almost useless because filled by fuel tank, car doesn't start on GPL/methane during winter unless you've warmed it up, which usually means you've already arrived where you have to)--no, please don't increase fuel taxes AGAIN. we already pay all sorts of crazy stuff with those

author: Berni
author_rank: Super Contributor
timestamp: September 29, 2016, 10:52:44 am
content: Quote from: kaz911 on September 29, 2016, 10:02:45 amYeah they usually like to be on the safe side with speedometers. Usually they take in to consideration the worst case scenario with the largest wheels that are allowed to go on plus max tolerance on those etc.I wonder if new cars with GPS tightly integrated in its computers use the chance to calibrate the speedometer error.

author: tszaboo
author_rank: Super Contributor
timestamp: September 29, 2016, 11:12:45 am
content: Quote from: Jeroen3 on September 29, 2016, 10:13:12 amHalf the cars being sold in west europe are diesels. Tax on diesel is less than fuel, because they thought it emits less CO2 (well, it doesnt). Such a moronic short sighted thing to do, I'm not surprised, they are politicians after all.I dont know about you, but I'm being charged based on cylinder capacity for the ownership taxes. It is quite high, especially since I have an Atkinson cycle hybrid. Bigger cylinder, more efficient, less power than similar Otto cycle. They dont even take into account the fact, that it is a hybrid. Now, nobody makes diesel hybrids. Diesel has to die. It belongs to tractors and generators, not cars.Quote from: kaz911 on September 29, 2016, 10:02:45 amLaw said it should be lower than actual speed. What upsets me most, there is a road, perfect for going 90, without traffic, I usually go 110 safely on it (I'm like the germans when it comes to this). Then they put up a 70 sign, because fuck drivers thats why. And then some old guy comes along, in their Pegueot 206, driving 60, unless something scary is on the road, like other cars, they slow down. I always said, whenever you want to buy a new Pegueot, they should just take away your driving license. You obviously cannot drive, dont have common sense, and cannot read, and hate cars.

author: Jeroen3
author_rank: Super Contributor
timestamp: September 29, 2016, 11:45:34 am
content: Quote from: NANDBlog on September 29, 2016, 11:12:45 amThere is an ad going around with the first diesel hybrid. Was is Volvo?Meanwhile. Ownership tax in the Netherlands included in a graph I made.(correctness not guaranted, I reverse engineered the javascript online calculator since the tax agency does not publish a table or formula)However, owning a car is still cheaper than in Singapore. There you have to get the license plate through government auction.

author: SteveyG
author_rank: Unknown
timestamp: September 29, 2016, 12:18:20 pm
content: You guys must have dodgy cars. Both my Beamer and Ford are spot on with the Fuel gauge.Quote from: kaz911 on September 29, 2016, 10:02:45 amIt's done on purpose, typically they read 10% low to take into account tyre inflation or people changing wheels.

author: macboy
author_rank: Super Contributor
timestamp: September 29, 2016, 01:26:19 pm
content: Quote from: SteveyG on September 29, 2016, 12:18:20 pmThe fuel gauge on my 2006 Lincoln LS was always very linear and accurate. The speedometer was accurate also. It read with +-1 km/h of what a Garmin handheld GPS would indicate. I have never heard of a speedometer being 10% low intentionally. That is what we call an "old wive's tale". Speedometers these days are extremely accurate, unless you change the tire/wheel size or severely under- or over-inflate the tires.As for people driving slowly in the fast lane... those are just idiots. You do realize of course that the world is filled with many of them?

author: meeder
author_rank: Regular Contributor
timestamp: September 29, 2016, 03:40:03 pm
content: VW had a tendency to make the speedometer less accurate. In the old days 10% was quite normal with mechanical speedometers. Nowadays they mostly use the ABS sensors to determine the speed. Even in recent years I saw VW's with a 10% deviation but only above 120km/h, up to about 100km/h it was quite accurate but once you got above that speed it became less accurate. The scale wasn't linear as well, the first half was 0-120 and the second half was 120-280.

author: kaz911
author_rank: Super Contributor
timestamp: September 29, 2016, 08:45:38 pm
content: Quote from: macboy on September 29, 2016, 01:26:19 pmI have not driven in the States for a while - but all over Europe in the brands i mentioned - in all the different cars - clocked with GPS or 2 different GPS units - usually on cruise control on straight road over long time - not a single one was right above 100 km/h - I check tire pressure and tires every time and everything to specs. Mercedes was the one with the least issues.

author: LaserSteve
author_rank: Super Contributor
timestamp: September 29, 2016, 09:26:46 pm
content: Hate to spoil all your fun, but a National TV Evening News personality tracked down a Fuel Gauge Designer a few years ago. During the seven minute or so interview, much was discussed, including the psychology of the indicated curve used, and a hidden reserve designed in. The fuel gauge is thus designed to make normal people happy and to protect them a bit.For us technical types, lack of an exact indication is maddening.Now if some one can tell me why I spend 7 hours driving Akron to St. Louis at 65-70 MPH, Then St. Louis to Chicago and Back to Akron the next day, and my average speed never gets higher then 35.4 MPH. (Chevy Product)The Fuel Gauge in my Honda is beautiful, has good repeatability, but is meaningless. What does work well is the Predicted Miles Remaining display, which looks at remaining fuel quantity and current speed and calculates effective range. Heck, That's reasonably accurate in the Chevy Cruze, too.Steve

author: Nerull
author_rank: Frequent Contributor
timestamp: September 29, 2016, 10:18:36 pm
content: Quote from: Red Squirrel on September 26, 2016, 07:22:44 pmYou probably should try reading the instructions, since it sounds like a standard propane tank thermal gauge.

author: ajm8127
author_rank: Contributor
timestamp: September 29, 2016, 10:42:57 pm
content: The fuel gauge on my E90 BMW is pretty linear. I characterized it over the course of half a year as a study to develop a formula to use when blending my own fuel (gasoline and E85). I had noticed error on previous vehicles related to ambient temperature (poor TCR of the pot I guess) so I tracked that, the reading on the gauge and the fuel I put in.http://www.bimmerboost.com/showthread.php?45780-335-Fuel-Sensor-CharactorizationTemperature didn't seem to have much of an effect so they are either correcting for it or using something else like encoders or pots with low TCR.All in all it has about a 2 gallon reserve, but is surprising linear through most of the range up to its capacity of 16 gallons. Best of all the car makes about 30-40 more horsepower with E30 over E10 (regular gasoline in the US is about 10% ethanol) due the the latent heat and detonation resistance advantages of ethanol and tuning to take advantage of those properties.The speedometer does read a few percent high, however. Oddly enough the car knows exactly how fast it is moving because I can read the "true" speed from the ODB-II port, but the speedometer is always 3% higher or so. It's not a fixed offset so I don't think it's just something like the needle not being perfectly installed. I am convinced it is an intentional design decision.

author: Someone
author_rank: Super Contributor
timestamp: September 29, 2016, 11:16:40 pm
content: Quote from: NANDBlog on September 29, 2016, 11:12:45 amMercedes, PSA, and VAG all have diesel-electric hybrid platforms.And historically diesel fuelled cars produced much less CO2/km through more efficient engines. Thats disappearing now that emissions controls are focusing on other pollutants and the efficiency of petrol engines are rapidly improving. Its only once you try and balance all GHG emissions the petrol engines are more efficient:http://green-budget.eu/wp-content/uploads/2016-02-17_Helmers_European-diesel-car-bias-makes-climate-worse1.pdfAs usual the government is slow to change while technology is rapidly moved forward by economics (car makers looking for the profit).

author: SkyMaster
author_rank: Frequent Contributor
timestamp: September 30, 2016, 01:07:12 am
content: On a VW Golf Mk 4 2001, when the speedometer sensor is disconnected, the fuel gauge seems to lose its averaging function; without the speed sensor, when the cars is driven, the fuel gauge needle is jumping around. It is jumping around slowing, and is nowhere as stable as when the speed sensor is connected.It seems that the averaging function is using the car velocity in some way.

author: SteveyG
author_rank: Unknown
timestamp: September 30, 2016, 06:33:47 pm
content: Quote from: macboy on September 29, 2016, 01:26:19 pmNo old wives tale. Read the speed over ODB or through the diagnostics menu on both my Beemer and Ford and the speed is spot on, but at the same time you can see the dial is set 10% less. There's even a correction factor in the BMW Standard Tools program you can use to edit the config on your car.

author: SteveyG
author_rank: Unknown
timestamp: September 30, 2016, 06:37:35 pm
content: Quote from: ajm8127 on September 29, 2016, 10:42:57 pmYou can edit this error in the software if you have a suitable ODB-II adaptor. The true speed is known to the vehicle as you said, but the speedo gauge intentionally has a gain error.