From: jfh@cs.brown.edu (John F. Hughes)
Subject: Overheating problem
Organization: Brown University Department of Computer Science
Distribution: usa
Date: Mon, 7 Sep 1992 15:21:34 GMT

I have a problem. Perhaps describing it as an overheating problem is
prejudicial, so let me just describe the circs:

We left Nantucket with a following breeze which died to nothing about 5 miles
from our mooring, so we fired up the engine, a Westerbeke 4-107 diesel with
fresh-water cooling. After running it for a little while, I heard the pump for
the house fresh water (i.e., drinking water) come on. "Funny," I thought, "No
one has used the taps..." but then the pump shut off again. "Hmmm. I suppose
that a little pressure has just flowed out from the pipes, or perhaps they've
warmed up and expanded a tiny bit in the engine compartment, and the pressure
dropped below 40 lbs/sq in, so the pump triggered," I thought to myself.

   During this time, then engine temperature had risen to about 185-190 on the
meter. A little high, but within reason. I'd checked the oil, xmission oil, and
cooling water before setting out, so I knew that things were generally OK.
Aside from a very slow drip in one of my fuel feed lines--I think I need new
washers--everything with the engine's been going pretty well recently. 

   Anyhow, soon the drinking water pump cycled on and off again, and I went
below to look around. Sure enough, the hot water heat exchanger (which heats the
drinking water using hot engine water) had a slow drip at the forward end. 
Bummer. I practiced the sailor's mantra: "What the hell, it's only money." 
Turned off the power to the drinking water supply, and added an item to my 
Do List.

   Back on deck, I looked at the temp gauge, and it was saying something closer 
to 200. That's a bit high, and I started to worry. But we w're nearly at the
mooring, so I just ran on in. I figured "Next time we go out, I'll have some
tinkering to do before we leave."

   So the next time comes. I remove the drinking water heat exchanger, and take 
the two hoses from the engine and join them with an elbow, and do the same 
with the two hoses from the drinking water system. No more cycling water pump, 
so the drinking water side is all happy (except that I happen to need a new 
pump, too, since the old one it rapidly dying, and is held together with 
bubblegum and prayer with hopes of lasting through the season. 

   During the removal of the exchanger, I lose lots of antifreeze from the
hoses, so I top up the expansion tank, and fire up the engine to see how things
work. Well, my wife's in the cockpit, watching the temp gauge, and it goes up
to 180 (the thermostat's nominal setting) and then beyond. I've got the cap of
the expansion tank off, and I've poured in a little more antifreeze and the
bubbles work their way out of the system, but when the temp gauge says 210, I
tell her to shut it down, and I swear a little. "What the hell is going on?," I
ask. "Perhaps a bad thermostat?" I reach back and put my hand on the engine
raw/fresh water heat exchanger, and it's cool to the touch. Warmer than the
seawater by a little bit, but basically cool. With the engine water temp at
210? Wha???

   I let her cool down for half an hour, and try it again. This time the temp
rises to about 200-205 and steadies off. I figure I've got more things to worry
about, so we cool off and use the startup time on the thrid start to putter
back out to our mooring. It's 10 PM, so it's about time for bed, whether the
engine's overheating or not. 

   Next morning, I get up, filled with energy, and swap in a new thermostat.
It's not hard work, and aside form getting a little permatex on my hands, it
goes well. Stove alcohol cleans up the permatex, and I'm ready to try the
engine. We fire it up, let it run, and...the temperature gauge rises to 210
again. But...the heat exchanger is still cool...I'm baffled. I remove the cover
from the expansion tank, holding it in a terrycloth towel, and wearing an oven
mitt, expecting lots of pressure and steam, and all I get is a little steam
rising from the hole...no pressure to speak of at all. The tank's got plenty of
fluid, and I figure "Maybe it's actually the temperature gauge. Perhaps 
*it*'s what's giving me the grief."

   So I crawl back into the seatlocker to look at the backside of the gauge,
and one of the nuts that hold the wires to it is a little loose. Not really
loose, but not tight either--I can loosen it with my hand. So I get my wrench
and tighten it up, figuring that I've found the problem, and all will be well.
I check the screw on the connection at the temperature gauge sender as
well---it's nice and tight, and there's no trace of looseness in the 
wire-terminal joint either. Looks good. 

   We eat breakfast, and an hour and a half later, I get to trying the engine
again. By now the engine block is cool to the touch--certainly no more than
about 90 degrees. When I fire it up, the temp gauge reads 60 degrees for a
moment, then jumps up to about 80, and then jumps (all this within about 15
seconds) to about 140. As it rises, the needle makes sudden excursions to temps
that around about 25 degrees lower than its farily steady (but rising)
readings. The it settles in at about 200. Still, the heat exchanger is cool,
and there's no pressure in the expansion tank. So I figure "What the hell, it
*seems* OK even if that *is* too high a reading," and we take off (under sail).
The two times we have to use the engine that weekend, the same thing happens:
temps from 200 to 220, but no pressure in the exp. tank, and the heat exchanger
only moderately warm.

   Any conjectures? I'll probably just *remove* the t'stat for the next time I
use her---that'll make her run at about 140 (or it did the last time), and
that's no great sin. I'll probably only put an hour or two more on the engine 
before haulout anyhow. But if anyone has ideas about what might be causing the
high temperature readings, I'd love to hear them. Powerboaters: this is your
chance to explain things to an ignorant sailor...I'm all ears.

-John
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