Years ago I read a study that showed that the hotter an engine ran without losing it's coolant, the less wear there was on engine wear surfaces. Anything close to 160 degrees saw really accelerated wear. 180 degrees was better, and 195 even better. My Corvette was programed to turn on the first fan at 215, and the second one at 225.

So there is definately some support out there for hot engines. However, I have asked a couple of guys playing with turbo cars, and they suggest a 185 theromostat, which kind of goes against this hot is better idea. Why would 185 be better? Once the thermostat opens, does it realy control anything anyway? It seems as if the fan control, and the radiator design would have more influence on the actual operating tyemperature of the engine. So does the thermostat actually influence the operating temperature of the engine? And, Is a cooler one in any way beneficial to a turbo car? Things get awfully hot under the hood, but it is mostly exhaust temps, and not engine heat radiating.

I've got more cooling system questions later, but let's start here.

What do you think?

Sam

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I dropped out of college before I took thermodynamics. But I would venture to guess that there are several factors involved in selecting ideal temperature ratings.

heat generating capacity of an engine
thermal absorption rates of the coolant
volume of coolant
heat dissipation ability of the radiator (based on cooling surface area)

I'm sure there are others. But I would venture that there is a threshold where you could exceed the cooling capacity of the system. I don't have a clue as to where this might be. But to keep things in a safe operating range and to plan for failures you provide for a certain margin for error.

There's also the issue of expansion with respect to the metal parts. If you heat these parts to say 250 F before the thermostat opens, then push coolant with a significant temperature difference through, you could conceivably cause some warpage. (Pulling numbers out of thin air, so correct me if I'm wrong.)

Another idea that struck me. Adding heat to an engine and it's various mechanical parts might change the materials properties such that they for instance change friction coefficients. I doubt it would be so hot as to change the metals' crystalline structures. But perhaps change electromagnetic properties?

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The Old Goat '83 D150 225-2

AKA Ice Titan

It's one of those balancing acts. A cooler engine allows a denser air/fuel charge but a hotter engine promotes better combustion. 195* has been the standard for many years on emission controlled engines because of that reason. Too cold and you have incomplete combustion and accelerated wear; too hot and you get reduced power and higher probability of preignition detonation. So, it's a tightrope that an engineer has to walk. For about the last 30 years it's been tilted toward warmer to reduce HC and CO emissions.

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David Kight
'62 Valiant Signet, White
'98 Dodge Dakota
'06 Jeep Liberty

Growing older is unavoidable but growing up is strictly optional.

Lowering coolant temp will raise the engine's knock resistance. Under normal conditions of light to moderate loads, higher coolant temps will reduce the amount of cylinder wall fuel wash which will reduce wear and emissions. But at WOT, your primary concern is knock control.

Injection timing plays a large role in bore wash. Firing on a closed intake valve gives greater fuel vaporization as opposed to firing on an open valve.

Mitch

So would you vote with the 185 guys, or stick with the 195 I have in there. I look at the temp on my slant, and it sits around 205 until I cut it off, and then it heat soaks up to maybe 225, with some percolating going on inside. I have the best possible aluminum cross flow radiator, so to bring the temp down, I would have to control it with fan temp switching on and off at lower temps, or a different thermostat. But, should I? Maybe the current temp is just fine. Then there are the guys who say put a 185 in a turbo engine.
Sam

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You'll get marginally better power with a 180 or 185 but I doubt that you would ever notice. The heat build up could be controlled with an electric fan programmed to run after the engine is shut off until the temp drops to a reasonable level. Truthfully with a good pressure cap and overflow tank along with the proper coolant mixture it shouldn't be a problem.

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David Kight
'62 Valiant Signet, White
'98 Dodge Dakota
'06 Jeep Liberty

Growing older is unavoidable but growing up is strictly optional.

I think the biggest reason to run an engine cooler, especially with forced induction, is to reduce detonation. This will help you max out power for both NA and turbo motors. Wear is worse and mileage will be worse.

I run my Darts w/195 tstats and they operate around 200-220 deg depending on weather/load.

Lou

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Home of Slant6-powered fun machines since 1988

I was just Monday reading a 1962 Chrysler engineering report on the effect of combustion efficiency of different thermostat temperatures. When I get home (I'm on vacation on the West Coast) I'll post the relevant details. The improvement in part-throttle combustion efficiency with a 195° rather than 180° thermostat is much larger than I expected!

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

I'd have to agree with most of the posts here. Hot does equal better mileage, cleaner engine and less wear. However keeping it cool is the way to go with a turbo engine to get the most out of any given octane. It makes a big difference in the amount of detonation you get. The internal cleanliness and wear are not an issue with an ester based synthetic like Redline. I would forget about a 180 and go with a 160. You get a denser charge as well. The next issue is whether or not the radiator and fans can keep it that cool. It will allow you to run the most boost / timing possible with whatever fuel you use. With a port injected engine response is not hurt at all if it is dialed in right. Mileage, well, not so much.

On a normally aspirated engine with a carb, I run a 180. It is very hot down here most of the year. If I lived somewhere cooler I would consider a 195. Even here a carbed engine will run like a pig with a 160 in the winter.

So how much of this temp control is the thermostat, and how much is the temp you have your electric fan turn on? It seems as if once the thermostat opens, the temp is controlled pretty much by other factors, and not the Tstat. It seems as if the tstat only controlls how fast you let it warm up. If it opens sooner, then the cold water comes into the block sooner, but eventually it gets warm, and acts the same as if it had a 180 or 195 in it. Am I wrong here? Just asking for thoughts and opinions.

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In stop and go traffic, with hardly any forward velocity, the electric fan turn-on point determines the temperature (unless it's below the thermostats temperature, in which case it would be on all the time).

Under normal cruise conditions, the thermostat will determine the temperature.

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Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

Brother, not me! In an ordinary case (no turbo), I'd flatly reject a 160° thermostat (if you neeed a cold thermostat to control pinging, there's something wrong), but in an extraordinary case like a turbo EFI engine, I'd probably try all the easily-available thermostats (160°, 180°, 195°, and maybe even 205°) and keep careful track of performance, driveability, mileage, and of course pinging. The best way to do it would be on a dyno, but that could get costly, so maybe just on-road tests with one or two tanks of fuel for each thermostat.

My guess is that after the test results were all in hand, I'd wind up with a 180° or a 195° thermostat.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

I thought we were talking about a EFI turbo engine running pump gas? I agree Dan, I would not use a 160 in a normal engine setup. I would use it given the parameters in my post, including the synthetic oil.

I have seen the data as well that shows that a temperature as high as 225 should produce the best power and mileage. My own experience agrees. Aside from strength the heat is one of the benefits of block filling in drag cars.
Trying, or getting, the most out of a turbo engine on pump gas is different and you can make more power at the lower temp. Yes the mileage may suffer. The emissions will be worse for sure. My guess would be and was the same as yours. But I have been through the testing and ended up with the 160 in my last turbo car. It is pretty much the standard with the exception being guys who live in the cold and need the heater to work better. I have run that setup more than 100,000 miles in all types of weather with no problems (other than the heater). I have seen it done on more turbo cars than I can count, and it works. Combustion temps are plenty high when you are jamming 2 or more atmespheres in there and then squeezing them 8-1.

In a normal car, I have never seen anything below 180 run best.

I disagree that synthetic oil is a mitigating factor. Quenchout caused by too-cold engine operating temperature will load up the oil with water, acid, and other byproducts of incomplete combustion whether the crankcase contains 69¢/quart no-name "recycled" motor oil or $12/qt Redline synthetic.
Surely. The limiting factor here is the ancillary effects of heat. It doesn't do any good to squeeze out more power if you can't use it 'cause you're stuck by the side of the road 'cause your carburetor's boiling, or your cooling system isn't up to the load, or whatever. And it's true, these older engines really weren't originally designed and configured to run significantly hotter than the OE thermostats caused them to run. But obviously, the balance of the equation changes depending on what kind of fuel system and cooling system we're running and what we're doing with the vehicle. If it's a dragster, that's one thing. An enduro racer, another situation. A street driver, different altogether again.
This is just what I'm talking about: What're we doing with the car? If it's a drag racer, then it's significant that we can make more power with a 160° thermostat, because we are trying to use every last bit of power we can make.

If we're driving on the street in a car that's not essentially underpowered to begin with, we essentially never get the chance to use anywhere near all the power we can make, so other factors (fuel economy, driveability, emissions, oil contamination) deserve consideration.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

We run a 180 degree thermostat in our lightly modified 225. Normally runs 190-200 under everyday driving conditions.

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