Mike,
I agree with your points regarding the thermodynamics of the system. You stated it better than I did. However, I have never seen an LT1/LT4 run at 180 even though the thermostat is 180. I have no reason to believe that my old thermostat was bad when comparing to the temperatures observed by everyone else. I never saw a temperature in my car that was different than personal observations in friend's cars or posted on the forum.

As far as my computer reprogramming goes, I observed the same temperatures with the 160 before I did the reprogramming. I didn't get a custom program until I installed headers and removed the cats, which was a couple months after I did the thermostat. I used to have a Hypertech Power Programmer (still do, it's for sale) and observed the same highway temperatures regardless of fan temperatures or programming.

 

I've been following this good discussion- and no name calling even :) So let's review:

The heat generation rate of the engine versus heat dissipation rate of the cooling system will determine the minimum operating temperature that can be achieved. Kevin your cooling system is obviously in great shape and capable of cooling your fairly stock engine to around 170 or less in your driving environment.

Assuming an adequate cooling system, the thermostat is there to raise that minimum temperature and keep the engine from running too cold. GM wants them running hotter for emissions; we want them cooler for better performance and possibly lower wear. Mike you are 99% correct and had excellent thermo explanations except: the thermostat's rating is the temperature at which it starts opening, not its fully open temp. It is fully open at 10-15 degrees above that.

So he's capable of operating around or below 170F, but the 160F thermostat isn't mostly/fully open till 173F which defines the minimum operating temp. With the 180F thermostat, it's fully open at say 193F which defines a higher minimum operating temp. And if he used the 195F like the L98's, we'd be seeing 207-210F. So that's what's going on in this specific case.

Unfortunately many of us suffer with a cooling system that cannot dissipate engine heat fast enough until the temp differential between outside air and coolant becomes higher; equilibrium is not achieved till 210F, 220F, 235F, etc. And this defines the minimum operating temperature- regardless of what thermostat is used (since they are all fully open by this point).

So I think someone owes me a case of beer.... :jester


P.S. With 115F in AZ, 500+ horses (=heat), and intercooler blocking the radiator, I'm running 230-240F; so quit yer whinin! And no thermostat is gonna fix that...



[Modified by gcrouse, 2:51 AM 6/19/2002]

 

gcrouse,

You are 99% correct sir. I have checked and I am wrong on the point at which a thermostat is fully open. According to relaible technical documentation the final fully open position for an automotive thermostat is approx 20 degrees F above the value stamped on the valve. This is also borne out by the recommendation of the 88 GM Factory Service Manual. which suggests testing for correct thermostat operation by immersing the thermostat in heated 33% glycol solution at 22 degrees above the stamped temperature value.

kkonen is correct too and again I was wrong about the 20 degree difference under the specific circumstances he described. Please accept my apology.

Please note however, that my original point which I still stand by, was that in traffic once you have reached a temperature above that at which the thermostats are fully open, the final maximum temp reached is not affected by either a 160 or a 180 thermostat. If you are seeing temps above 200 degrees changing to a 160 thermo will not stop that.

1% Although gcrouse has yet to show me "ANY college professor of Automotive Engineering" to satisfy my bet, I do conceed that he is correct as to the important facts and that I owe him beer, as well as an apology to all who have followed this thread for having previously posted information based upon my own misunderstanding and not verified fact. Gcrouse, the Phoenix Budweiser distributor Henslee & Co. says that they cannot let me buy the case directly for you to pick up, so you will need to email me your address and I'll send you a check for a case of Michelob.

Additionally, I have contacted folks at the STANT Thermostat Manufacturing Company and while I await a more complete response, I can tell you that they report the use of 4 different types of thermostats in Corvettes from 84 - 96. From their preliminary respone it APPEARS that there may even be differing cross sectional opening areas used. If true the difference is probably insignificant and due to manufacturing tolerances and not design. I'll post any useful or interesting info that I get it from them.

Mike

 

Man, what a thread !!!
Here are a few facts that any performance shop can veryfy:
1. If the radiator and the rest of the cooling system are in good shape and enough airflow throught the radiator exists (full fans or cruising at highway speeds), the engine operating temp is approx. 15 to 20 degrees higher than the thermostat rating.
2. The LT1 comes stock with a 180 degree thermostat
3. Changing to a 160 degre thermo, will have the engine running at 172-177/180 degrees when enough airflow exists.
4. If this can't be achieved with a 160 degree thermo, other issues exists with the cooling system.
5. GM used to install two types of radiators in the late C4s, a 1 3/8 thick and a 1" thick radiator. No matter, ifthey are clean and the cooling system is in good shape, they will cool equally well. GM is no longer supplying the thicker radiator as a spare part, only the thin version is available and also installed in the LS1 vette and f-body.

Temparature is greatly depending on many variables, but if the cooling system is in excellent shape and enough airflow exists, the engine temp will drop at the same rate the thermostat rating was dropped.

 

What a thred !
No name calling !
Very informative !
Ya got to love it :yesnod: :yesnod:
Hat's off to the gentelmen.
Congratulation's to all on a great post.

 

Has anyone considered the accuracy of their temperature gauge. With a 160 stat I can clearly see it crack open at 169. Now if I leave the car sit in a fairly constant temperature garage for a day or so and check both the oil temp and coolant temp before starting the car the coolant is consistantly 9 degrees warmer than the oil. They should be the same. When I first got the car (96 LT4) I questioned the dealer and they stated the coolant gauge wasn't reading the same temp that the thermostat saw(factory stat). Later after seeing the discrepency between the oil & coolant gauges I asked the dealership to check it out. They charged me $69 to tell me all the components were in spec and nothing could be done under warrenty. The dealer is Spitzer in Amherst, Ohio.

 

Yep- I've been trying to get this point across to people for years! They are limited by the cooling system's rate of thermal dissipation; what is needed is a better radiator and more airflow thru it.

This is really too much; I'll gladly accept a virtual beer :cheers:

I'm just happy we've reached a consensus and that people reading the thread have learned something.

 

I used to think that way. All the theory supports it, but practice does not. In traffic with stock everything, I was around 230*. I reprogrammed the fans to come on at 210, off at 205(Hypertech). Now my temps never got up to 220*. Next, I installed the 160* thermostat and reprogrammed the fans to come on about 165. I now NEVER see 200 in traffic. I think (I may remember incorrectly) that I got up to 215 when I was hot-lapping an autox track in 90* weather. As I am sure you know, this is the most intense thing you can do to a car. Since the speeds are low, there is not the air flow you get on a road course. As soon as I stopped the car, the temp dropped rapidly.

I will admit that I do not live in a big city, so I may not have the time to build up excessively high temperatures. One thing the lower temp thermostat will do is give you time. In traffic, you will be generating more heat than the cooling system can dissipate. Once you start moving, it will cool the engine to a lower point. When you slow or stop again, the temperature will rise but the max temperature will be lower since it started out from a lower point.

Everything I am saying about thermostats is assuming that the radiator is clean and in good working order. If the radiator is blocked, or clogged, you have more problems than worrying about a thermostat.

 

OK, you're all wrong and the answers are so intrinsicly obvious as to preclude the need for explaination.


:D :D :D

 

Yes, but you didn't just change the thermostat. By turning the fans on earlier and increasing airflow thru the radiator, you greatly improved the cooling system's heat dissipation at that lower temperature. In effect, leaving the fans off until a certain temp is reached raises the minimum coolant temp (when not moving). Since the system was now removing more heat and capable of cooling the engine to a lower temp, your lower temp thermostat allowed you to reduce the minimum operating temp. So you proved the theory.

It's good you understand that the fan ON temp and thermostat are related when in traffic and low speed auto-x. No thermostat can lower the engine temp below that of the coolant. Without free airflow, that coolant temp is regulated by the fan turn-on and turn-off temps. If you hadn't lowered these, the 160 stat alone could not have lowered your operating temp. It's a matched system.

So for those interested, here's the equation:

Heat dissipation (BTU/min) = Krad * Arad * (Mair/min) * (Tair - Trad)

Krad : radiator material (copper/alum) coefficient thermal conductivity
Arad : radiator surface area that air passes over
Mair/min : total mass of air passing over that surface in 1 minute
Tair : temp of air
Trad : temp of radiator (coolant)

All other factors being equal:
1) Materials with higher themal conductivity (copper/alum) will transfer more heat
2) Greater radiator surface area will transfer more heat
3) More air mass flowing over the radiator surface per time will transfer more heat.
4) The higher the temperature differential (between air / radiator) the more heat is transferred. (This is what allows the system to reach equilibrium instead of spiralling out of control.)


[Modified by gcrouse, 1:08 PM 6/20/2002]

 

Great Discussions in this thread.

My '89 was running way hot - 247* idling in traffic jam when it was 106* out. Ran about 207* with A/C on cruising on open highway with outside temps in 105-6 degree range.

So, I installed: 160* stat, Hypertech ThermoMaster chip, hi flow pump, aux fan switch (200* on - 185* off), new hoses, and a Ron Davis Racing dual core aluminum radiator.

Results: 109 degree day - A/C on idling in traffic behind wreck for 20 minutes pushed it to 215*. Cooled to a steady 189* on the same 109 degree day on open highway with A/C on. Last Saturday night returning from Tucson with temps right at 100* and the A/C on, it was down to 167* cruising (with 5 Vettes) at a steady 85-100 MPH. Yesterday morning on the way to work, I left the A/C off - 89* outside - coolant temps held 167* during open highway cruising and climbed "all the way" to 177* when I was sitting at a long light for a couple of minutes near work.

Question - Do you think I should switch the stat to a 180* instead of the 160* so it doesn't run too cold in cooler weather? I'm assuming that 160* is a bit on the cold side, even with the chip. And, from the above, I think it will run near the 160* mark druing cooler months. With the 180* stat, it shouldn't run any hotter during the summer anyway - I hope.

Looking for opinions. Thanks, Paul

 

How cold does it get there? Your engine will reach operating temperature if you avoid extreme cold conditions. My car had no problem getting up to temperature in outside temperatures down to about 20-25*. I live in Texas it just doesn't get that cold here. Even with the colder thermostat, we have all agreed that the engine will not operate below the thermostat opening temperature. Of course this assumes that the engine can reach 160 or 180. One thing to remember, if it can't reach 160, it sure won't reach 180.

Something for everyone to ponder in this little thermodynamics discussion. Comparing "too cold" between LT1 and L98 is comparing apples and oranges. The coolant in an LT1 enters the heads first and is heated in the heads so that the coolant temperature in the block is significantly higher in an LT1 than the cooled coolant that returns straight from the radiator into the block. This is my reasoning for the use of a stock 180 thermostat in a LT1 and 195* in an L98. By using this logic, a 160 may be too cold for an L98 but not for an LT1. I don't know if this logic is correct, but it is definitely something to think about for those that have way too much time to ponder thermodynamics.

Also, a question for our local engineering professors, what does the term "too cold" mean? Is it just referring to keeping the oil warm enough so that it can lubricate effectively or does it have something to do with the thermodynamic processes in the combustion process?

 

Oil below 180F does not flow/lubricate properly and would be considered "too cold". If you ever install an oil cooler, it must have a thermostat to prevent the oil from reaching proper operating temp. In fact the Z51 "cooler" actually warms the oil when it's cold.

As far as engine temps, cooler cylinder heads are more resistant to detonation, cooler intake manifold packs a denser air charge, etc. So cooler is better- withing reason. Problem is at really low temps, engine wear (especially cylinder walls) is greatly increased. I don't remember the exact temp but I know cylinder wear increased at 160F. It reached lowest wear in the 175-250 range, but of course really high temps have other detrimental effects. IMHO an engine running 175-195F with oil about 10* above that is just about perfect.

And yes, an interesting point about L98 vs LT1 thermostats. The L98 stat is exposed to the hottest water coming directly out of the cylinder heads. At least they both have the temp sensors in the heads though so we can accurately compare operating temps.

 

Below is a graph of engine temp vs. cylinder wall wear I was mentioning; note it pretty much bottoms-out at 180F.


The page itself has interesting info on thermostats.
http://performanceunlimited.com/illu...ermostats.html

[Modified by gcrouse, 4:32 PM 6/20/2002]

 

gcrouse,

Excellent information! It has always been my understanding that SAE tests automotive oils at a minimum of 180 degrees and this is the minimum temperature level that you want your oil temp. Using a 180 thermostst pretty much gaurantees the oil will stay above 180.

kkonen, you bring up an excellent point also, the coolant flow characteristics of the LT1 and L98 are very different and what is optimal for one engine may very well be less so for the other.

With respect to racing conditions and coolant flow here is an interesting perspective. According to Smokey Yunick (one of the greatest smallblock Chevy engine builders ever in my opinion) in his book "Power Secrets" on page 121, he says "Some guys go to great lengths to keep the engine temperature down to 180 degrees. And, though the engine doesn't overheat, they don't realize that they're putting energy (heat) into the cooling system that could be used to produce power at the crankshaft. Running an engine at 180 degrees will drop the overall horespower by 2-3%. For max power the coolant temperature should be at least 200 degrees, and you should have at least 25 pounds of pressure in the system. Actually, a racing engine like the smallblock Chevy will produce more horsepower as the operating temperature is increased, all the way up to a maximum limit of about 220 degrees. This can be confirmed with dyno testing, but I would not unconditionally recommend that any engine be raced at 220 degrees. ...at 220 degrees you're right on the edge. Nonetheless, for maximum power output, the coolant temperature in a racing engine should be in the 200-210 degree range, measured at the point where the coolant is returned to the radiator."

This would seem to match exactly with the stock fan settings by Chevrolet. Both of the fans on my Z51were kicked in by 223 degrees under factory settings. Maybe the Engineers at Chevy think ole Smokey knows what he's talking about.

More interesting data for those still reading. According to the fine folks at STANT who manufactured the OEM thermostats used in the Corvette, there were 4 different types of thermostats used in Corvettes from 1984 - 96. Of the 4 types there were 3 significant differences based upon cross sectional flow area. As might be expected, the differences appear to be based upon engine type. L98, LT1, LT5. Note that the LT4 thermo does not appear to have differed enough from the LT1 to be mentioned seperately when it came to the reply from Denis Chadwick of
Aftermarket Services, Standard-Thomson (STANT) shown below:

86-91 Corvette 5.7L VIN 8
Stant 13359
Valve diameter - 1.00"
Min. stroke @ full open - .310

90-95 Corvette 5.7L VIN J
Stant 14068
Valve diameter - 1.12"
Min. stroke @ full open - .320

92-96 Corvette 5.7L VIN P
Stant 14218
Valve diameter - 1.640"
Min. stroke @ full open - .320

The LT1/LT4 stock thermostst it would seem is considerably different from the L98 and LT5 in ability to open up a lot more area to coolant flow.

 

Using the graph, the ideal performance water temperature is 170 to 190. With a 160 thermostat in my LT1, my water temperature is a low of 173 and a high of about 187. So this makes it fall, dead center in the performance category. Since my car is primarily a race car, a 160* thermostat makes my car perform ideally according to the graph and that a 180* thermostat would make it run too hot for performance issues.

I have been told this before. I have even gone through the thermodynamics of the adiabatic expansion (power stroke) and can show the theory as to why a hotter engine is more efficient. For an LT1, it can be easily shown with a dyno that a 160 makes more power. I have a friend that has performed the experiment. MTI also told me that the reason my car dynoed so low is due to the higher engine temperature. I think he has dynoed enough cars to know if it works. Before anyone asks, he didn't try to sell me one. I believe the resason for this is that the LT1 runs with a warmer block than an L98 with the same temperature thermostat due to the reverse cooling.
http://ws6.com/mod-3.htm is a dyno chart of before and after a 160* thermostat. I will concede that he has added the Hypertech Power Porgrammer (I assume power tuning). According to my drag strip results, the power tuning has no effect on power. The times before and after the tuning were identical for all practical purposes. I made the program change at the track so the results would be under the same conditions.