From: mshar@mentor.cc.purdue.edu (Mike Mshar)
Newsgroups: rec.autos
Subject: Re: Cooling problem
Date: 2 Oct 92 20:12:21 GMT
Organization: Purdue University Computing Center

In article <1992Oct1.231546.5249@sol.UVic.CA> atovorni@engr.UVic.CA writes:

[Long explination of temperature needle fluctuations deleted, since I 
 already said it all earlier]


>   It is also normal for the stuff to evaporate out of the overflow canister.
>This is alright. That canister only keeps the coolant from splashing all over the road if your engine really overheats. Mine's always dry. The way to really check
>your coolant is to remove the rad cap and look into the rad. Mine's always

Well, I filled my overfill tank to the cold line this summer (sometime in
May) and it is still at that mark. If the container is enclosed (with the 
exception of the small spill-over hole or hose) then you should not be
constantly losing coolant from the tank, at least not once every couple
of weeks. The purpose of the tank is NOT to just catch the liquid in
case of an overheat. It is there because cooling systems are pressurized.
The radiator should be kept full to the cap, and there should always
be coolant in the tank. Why? Well, when the car warms up, and the coolant
gets hot, it expands. When this happens, the pressure in the cooling system
increases. This pressure increase was incorporated into the design to
allow the coolant to reach a higher temperature without boiling. When the 
pressure reaches a certain value (usually 16 pounds per square inch or 
so), the spring loaded part of the radiator cap will open, allowing some
of the coolant to spill over into the plastic can. Thus, a constant pressure
is maintained.

Now here is the part most people don`t think about. When the car cools down,
a vacuum builds up inside the radiator. This happens because there is 
less volume of water in the cooling system due to the spill-over of 
antifreeze into the plastic tank. When this vacuum forms, the radiator
cap releases its seal, and allows coolant from the tank to reenter the 
radiator, since the neck of the radiator is attched to a hose that is
submerged in the coolant in the plastic tank. Thus, the radiator is always
completely full of coolant, even with the temperature and pressure
changes in the system. So, with this system, you don`t have to leave
some of your radiator empty for water expansion, as was done on older
cars.

So, you should keep the plastic can full of coolant, and if the coolant
is disappearing from the can, it can only mean that coolant is 
being lost sometime during engine operation. The amount of coolant
in the can will drop a little during the fall, however, because the
water will get colder with the outside temperature, and thus it will
contract. This process will reverse itself in the spring.


>full, even if the plastic can is empty. Never do this with a hot engine. 
>Check it when the car has not been running for three hours.
>
>   A fluctuating temperature needle is normal, and so is coolant "disappearing"
>from the canister. Neither of these are reasons to trade in your car. Generally,
>if the car is a Honda, that's a good reason to trade it in anyway :=)
>
>Andy.

This is all right, however, except for the part about disappearing coolant.

>
>PLEASE EXCUSE MY OBVIOUS IGNORANCE. 

I will try, but it is hard sometimes. Read my .sig.

-- 
|       Michael G. Mshar        | My Life-Long Goal: To keep common sense    |
|   mmshar@mn.ecn.purdue.edu    | alive and keep the idiots from taking over.|
|  mshar@mentor.cc.purdue.edu   |     \\President, Nice Guys Anonymous//     |
|____>>> United States Steel, Mechanical Engineer, Technical Services <<<____|
Newsgroups: rec.autos