Kirk et al,
Imagine you have a 160 degree thermostat, and the coolant in your car is about
190 degrees under normal operating conditions. The thermostat will open at 160
degrees, and keep the coolant temperature down to, say, 165 degrees. Now
replace the thermostat with a 180 degree thermostat, and the thermostat will
open at 180 degrees and keep the coolant down to, say, 185 degrees.
Now imagine you have a 160 degree thermostat, and the coolant in your car is
about 150 degrees under normal operating conditions. The thermostat will remain
closed, and the coolant will remain at 150 degrees, right? Next, imagine you
change this for a 180 degree thermostat. This thermostat will also remain
closed, and the temperature of the coolant will stay at 150 - hence no change in
coolant temperature, despite fitting a hotter thermostat.
Next, go back to your 190 degree coolant. You're doing fine with a 160 degree
thermostat. Now, re-core your radiator. The coolant will be cooler than
before. (This is true even with the thermostat closed - the thermostat only
blocks off one route to the radiator. The other route is the return route - and
although coolant won't bed pumped this way, if the thermostat is closed, you'll
get a little bit of natural convection which will move liquid in all kinds of
strange directions, and some heat conduction too.) Imagine that the temperature
of the coolant now drops below 160 degrees. You're now into that area where
increasing the temperature of the thermostat won't necessarilly increase the
temperature of the coolant. But let's say you increase the temperature of the
thermostat significantly anyway. Then summer comes along. Now, the coolant
temperature goes up because of the hot weather. Because of the hotter
thermostat, the new radiator can't cool the coolant with the thermostat open as
well as the old radiator with the old thermostat could (despite the fact that it
cools better with the thermostat closed) so you overheat.
This is considerably simplified, because I doubt if I could get it right if I
tried to get all the details in! It's also an extreme case - I doubt very much
if the coolant temperatures would get as low as in the example if you were
stationary and there was no air-flow over the engine, for example. I didn't
suggest that you don't change your thermostat - you probably won't run into
problems if you do. I just suggested that you *might* have problems in the
summer, therefore you *might* like to not change your thermostat unless you
actually have a problem.
Could someone else please back me up on this one, just to confirm that I haven't
completely lost it? (Ok, so I lost it some time ago, but that's a different
story!)
Dean (probably talking complete and total codswallop again!)
-----------------------------------------
Enron Capital & Trade Resources Corp.
From: "Kirk Crawford"
<kirk.crawford@home.com>
25/10/99 15:45
To: spitfires@autox.team.net
cc: Dean Dashwood/LON/ECT@ECT
Subject: Re: Plenty-O-Cooling
> My temperature guage has always run at about the 1/4 mark except in very
hot
> weather (by English standards!) or in traffic for a long time, and I've
never
> worried about it. I don't know what thermostat I'm running with, though,
> because I've never bothered to look!
>
> Remember that putting a hotter thermostat in won't necessarily make the
car run
> hotter. If it's running too cool to open the current thermostat, then a
hotter
> thermostat also won't open, and won't affect the temperature at all. In
fact,
> it might give you overheating problems in the summer. I'm not saying
don't
> change it, just make sure it really needs changing first!
I don't really understand that. A thermostat opens at its rated
temperature, thus keeping the temperature of the car engine below or at that
temperature. I started with the 160 degree and the gauge got up to 1/4 of
the way. Now I tried a 180 (Stant didn't have a 190 at pep boys) and it is
about 7/16 of the way. Next I will probably go to a 185 to get it to be
exactly halfway. I am going to make sure that is what the gauge reads by
calibrating the gauge. To do this, I will put the sensor in a pan of hot
water with a candy thermometer.
If a thermostat is functioning, it cannot cause the car to overheat in the
summer. If it overheats in the summer with a functioning thermostat, the
car does not have enough cooling capacity. This is a function of the
radiator, not the thermostat. You can improve the cooling capacity by
fixing the radiator (recore it) or push more air accross it with an electric
fan or better cooling shrouds.
I suggest you replace your thermostat in your car. If it is always running
so cool, you are probably not getting the maximum mileage, and you want the
cylinders to come up to operating temperature so they can burn off any extra
fuel or stuff.
---
Kirk Crawford AIM:KirkBCraw
mailto:Kirk.Crawford@home.com
http://members.home.net/kirk.crawford/spitfire/
1968 Triumph Spitfire Mk3
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