Performance thermostat question.....

Main reason I'm asking is:

Not long ago I bought an '87 IROC 5.7 TPI L98, finally found one, been looking for about two years and figured this is my window of opportunity because now is probably the time to find them at reasonable prices.... another 5 to 10 years they will be pretty high priced I'd think...... anyway, these cars always seem to run really warm. A had a '94 Z-28 LT1 that also seemed to run on the warm side also. And my buddy's '93 LT1 is the same.

The IROC mostly sits in garage and I only drive it for fun in the warmer months (Btw, I'm located in Virginia) and really could go without a heater if it would help keep the engine temp down some..... Or I guess I could just install a 160 or 180-90 stat instead... What do you guys think? Who all here owns a L98 or LB9 or even an LT1? Do the LS1s also run fairly hot? I figure they probably stay a bit cooler being an all aluminum motor...... Bigjfig, Charles what do you think? I know Bigjfig will probably tell me to leave it alone because thats the way it came from the factory.....

Another thing, I've owned a few 5.0 GT Mustangs, two 5.0 H.O (L69) Z-28s, an LT1 Z-28 and I gotta say that this L98 IROC is the most fun vehicle to drive out of all of them..... even if it is an automatic. My LT1 had alot more top-end HP but the L98 has "loads" of low-end torque... I actually raced my pals '93 LT1 and spanked him out of the hole, by the 8th mile mark we were dead even and then his LT1 just walked me towards the end... man, you can really tach up those LT1s... The L98 just runs out of breath around 4,500 RPM...... I think I'll add some shorty headers and SLP runners..............fun stuff.

~John

John, that's a very interesting question that comes up from time to time so let's go back to the basics.

The basic heat transfer formula for two convective cooling mediums in a heat exchanger is:

Mc^T = Mc^T

where:

M = mass flow rate c is a heat transfer constant we will ignore since it doesn't change in this case ^T is the differential temperature between the heat exchanger inlet and outlet

Reducing the equation gives us:

M^T = M^T

Which we refine to a radiator in a car as:

M^Twater = M^Tair

So the only variables we are looking at are mass flow rate of water through the radiator and air flow through the radiator.

If the radiator has heat capacity greater than the heat generation of the engine then an increase in the mass flowrate of the water (by removing the obstruction to flow of the thermostat) with no change in air flow rate, with a constant air inlet and outlet temperature will result in a decrease of differential water temperature across the radiator. In the real world air outlet temperature will increase but let's ignore that for now since it will drive ^Twater up a bit. This gives us

^Twater = ^Tair/Mwater

Since Mwater is increasing ^Twater is decreasing.

A casual inspection of the above would lead to the conclusion the water is travelling too fast through the radiator and the engine coolant temperature will increase in the engine. But we aren't only dealing with water flow but mass flowrate through the engine. The greater mass of water flowing through the engine will have a higher heat capacity and will remove more heat from the engine which will drive down exit water temperature from the engine. If the radiator heat rejection rate exceeds the heat generation of the engine due to combustion, the engine coolant temperature will decrease at all points in the system, although the delta temperature across the radiator decreases.

When engineers design heat exchangers, the flowrate of the liquid (or liquids) must be taken into account but exceeding the design flowrate usually decreases heat transfer efficiency by a couple of percent so it's fairly negligible.

So based on the above we see that an increase in flowrate will remove more heat from the engine but that comes with a few caveats as follows:

• The radiator must be in good shape and must be large enough for the engine in the car.

• No external heat sources are added to the coolant such as a blown head gasket.

• The water pump capacity must be adequate to prevent departure from nucleate boiling.

• The increased flowrate must not suck the lower radiator hose flat and lead to cavitation.

• The radiator fans (and air flow at speed) must be able to pass enough air through the radiator to prevent overheating at idle.

• Warmup time to operating temperature will increase (running the A/C helps in a warmup) and oil pressure may be unacceptably high (in the case of a high volume oil pump).

Another aspect is cylinder wear versus engine temperature. Running the engine below it's design temperature means the bores are tighter and the rate of ring and cylinder wall wear will increase. This is a factor since the engine will take longer to heat up to whatever stable temperature the engine coolant ends up at and that temperature may be below optimum.

So as we following this path to it's bitter end, it's intuitively obvious to the most casual observer that removing a thermostat to bandaid a problem in the cooling system will have a negligible effect but if you are in the borderline case that increasing the horsepower of your engine has strained the radiator to it's limit, removing the thermostat might prevent incurring the cost of a very expensive aluminum radiator.

Keep in mind that air flow and engine heat output vary with speed and engine load but if the radiator can remove more heat that the engine can produce at all times the engine coolant temperature can still be controlled.

I took this option in my wife's vette back in 92 and have had no problems since but I do make sure I have time to warm the engine up before driving it.

Test it and see what happens. An o-ring style water neck is a great help when swapping to different (or no) thermostats.

Dave

PS - It's late, I'm tired so take all this with a grain of salt. ;^)

Go with a good 160 degree thermostat. Hypertech used to make a fan switch to go with them. Now if you want to cool your intake charge, you need to ditch the coolant pipes to the throttle body. I have thought about running them to a cool can before and using a small electric pump to cool the intake tract.

As for running no thermostat on the street? Bad Idea. Even most racers that run SBC's with no thermostat use a restrictor in the housing. This does two things. Restricts flow to the point that the engine can heat up. As well as prevents cavitation in the water neck. Charles

I have to weigh in on this one. Something that few people think about when they talk about keeping overheating problems away is the condensation of blow-by gases and the formation of sludge and varnish at lower engine temperatures. Years ago thermostats were all 160` to 165`. Then they all changed to 180` . Now 195`s are the most common. The reason is the factory figured out that a clean engine doesn't wear nearly as much as one coated internally with sludge. Removing the thermostat greatly increases the amount of TIME the engine operates UNDER 180` and the resulting formation of sludge. The reason the draggers use restrictors instead of thermostats is that they want to keep the engine as cold as possible for maximum power. They know the engine isn't going to be run for for any length of time as opposed to the street. A fully open high flow thermostat flows as many GPM or more than the restrictor. Once the coolant hits 190`-195` (thermostat wide open) it doesn't make any difference if there is a thermostat in it or not (cavitation aside). On the L98 it isn't going to make much difference because the electric cooling fans aren't going to come on until 190` anyway, making pumping all of that water thru the radiator pointless. If you want to help keep the temps below 230` work on getting more air thru the radiator. And make sure the Air Dam hasn't been taken off because it "got in the way too much". It removes the bulk of the heat produced by the engine above idle. About "heat bloom": The 3rd gen F-body relys on the forward motion of car to push air into the dam and up thru the radiator. When the engine has been pulling the car at highway speeds and it rolls to a stop, the block and heads are still releasing stored heat into the coolant like the engine was still pulling the car. The fans only remove heat fast enough to keep the engine cool at idle on a hot day. The coolant temp will climb whenever this happens until the block & heads cool (normal). This is why all aluminum engines appear to run cooler. The metal stores less heat because it is lighter. Actually iron that is painted black radiates heat faster than shiny aluminum. (G) This is not very significant anyway because the amount of radiant heat lost by the engine is a drop in the bucket compared to what the radiator is doing. In a nutshell, you could do more to keep engine temps down by checking the air ducting in front of the radiator for leaks & missing parts, and making the fans come on at a lower temp. (exiting soapbox) Andy W. p.s. surely your car doesn't have only one fan in it?

"John King" wrote in message news:oDWOd.189434$ snipped-for-privacy@bgtnsc05-news.ops.worldnet.att.net...

p.s. surely your car doesn't have only one fan in it? =================================== It has the dual fan setup..... Thanks for your input.

Actually I think I might buy the fan switch setup and stat from

For real...You guys are awesome.!!