Can you run and engine too cool to be safe?

I have a 1974 F100 two wheel drive, 390, C6. I rebuilt it about 6 years ago. I kept a stock water pump (in college at the time, couldn't justify spending three times as much for a high volume), but put in a high volume 160 degree thremostat and a 3-core radiator. Replaced the fan shroud, too.

This truck runs very cool. Bottom end of the "normal" range on the stock thermometer on even the hottest summer days. Barely gets to normal in the dead of winter. Personally, I like it. No worries about overheating (see related post regarding a 360 I have that's getting too hot).

Is running cold going to cost me engine life? I really can't see any problems, but other have said it would gum up my oil. I change the oil regularly, and it's always a good viscosity, just dark by oil change.

I want to run my 4X4 cool like this, too, especially since full time four wheel drive will put added demand on the engine. But, I don't want to shorten the engine's life, either.

Any thoughts appreciated.

Matt

 

Matt,yes you can overcool an engine. It sounds like you alraedy are. I read your other post as well. Don't even think about a 160* stat, that is way too cold. Don't go any colder than 190*, ever. If you study some physics, aluminum (pistons) sliding on cast iron (cylinder bores) has the lowest coeeficient of friction at around 225 degrees. As things get colder, your friction rises dramaticly. The curve gets steeper at around 180*. At 160*, you are shortening you engine life by 1/2 to 2/3s, and getting less power and fuel economy as well. I run all of my stuff @ 205*, cause that is the hotttest stat I could find. DF

 

Ditto. The best possible cooling system is one that keeps the engine at its optimum operating temperature under all conditions. That would mean a massive radiator with constant airflow, and a fairly high temp thermostat. A lower temp thermostat never helps.

 

Again, thanks to both karlsd and DF.

I will change this stat ASAP. Sounds like using the stat for 18000 miles might be more like 54000 in terms of wear. Oh, well. At least now I know. However, I'm a little excited, too. If using this stat has hurt my power, then it will be interesting to see what I have on tap with a higher temp.

If running engines that cold is so bad, why do they even make stats that low? Or is it application-specific? I'm a sponge for this kind of knowledge, to anything would be great.

Thanks again, guys. Looks like I know what I'll be doing tomorrow.

Matt

 

Again, haven't had time to do much. But I have had time to think.

I'll concede that I'm wearing my engine due to the prolonged cooler running temperature. But isn't it true that, even with a lower temp stat, the engine will eventually reach the same temp it would with the higher temp stat, at least close to the same temp? I'm still going to change it (sitting on the seat, actually, just waiting), but I wanted to see if I'm way off.

Matt

 

No. Essentially, the thermostat in your engine determines when the engine is warm enough that coolant needs to be diverted through the radiator. Assuming your radiator has sufficient capacity, and airflow through it is adequate, the thermostat sets the upper limit on the operating temperature.

For example, when you first start your engine on a day where the ambient temp is 72 degrees, the coolant is also at 72 degrees. As it circulates around the extremely hot cylinders and combustion chambers, it picks up heat from them and its temperature begins to rise. During this time, the thermostat is closed and coolant is not flowing through the radiator. Once the coolant temp reaches the temp that the thermostat is calibrated for, the thermostat opens and allows coolant to flow through the radiator. The radiator is designed to transfer heat out of the coolant, so it leaves at a lower temperature than it entered. It then, of course, flows back into the engine, where it picks up heat again.

The thermostat, therefore, determines when the radiator turns on and starts removing heat from the coolant. If you have a 160 degree stat, the coolant starts getting diverted to the radiator at around 150-155 degrees. If you have a 195 stat, the coolant will get 35 degrees warmer before the radiator starts operating.

If you have an adequately sized radiator and fan, and a 160 stat, your coolant will never get any warmer than 160. Similarly, a 195 stat and an adequately sized radiator means the coolant will never get warmer than 195. Thus, your "operating temp" us determined by the stat, unless your engine is generating more heat than the radiator can dissipate. In that case, you will eventually overheat and boil over, regardless of whether you have a 160 or a 195 stat.

 

Karl, I’ll go along with that except the ‘stat sets the LOWER limit for the operating temp. if I’m thinking straight today. I think you inferred that later. The temp. of the 'stat is when it just begins to crack open, they are fully open 15-20 degrees higher.

Barry

[link:www.ford-trucks.com/guidelines.html | FTE Moderator]

 

I stand corrected on that point. I was thinking that it was fully open at the stated temp, but you are correct that the stated temp is when it starts to open.

Nevertheless, I stand by my assertion that the stat does determine the engine's normal operating temperature. An engine with adequate radiator and airflow will operate at 160-170 degrees with a 160 degree stat, and at 195-205 with a 195 degree stat. The key point is that changing to a lower temp stat reduces the normal operating temp of the engine, which you don't want to do for ahost of reasons. It does NOT do anything about an overheating problem.

 

Agreed. I think we are just saying it differently.

Barry

[link:www.ford-trucks.com/guidelines.html | FTE Moderator]

 

My 2 pennies, I agree, go with the higher thermostat (190).

Think if it like this, the thermostat in your house regulates the temperature of your living space. When all else is working as it should, no matter the temp outside, it stays the same inside. An engines thermostat works the same way.

 

Thanks to all. I have a 190 ready to go in. First, though, I have to overhaul (read "replace") the cooling system in my other truck, and make sure it's running fine just in case I need to make a parts store run. Radiator is so clogged up on that truck that when the stat opens up, the top tank fills way faster than it can drain down. It's running too hot (top end of normal).

Okay, so anyone want to tell me how badly I've damaged this engine in six years and 18,000 miles by running it too cold? Obviously, I don't drive it a whole lot, mostly stop and go. No excessive metal on the magnetic drain plug, oil isn't metallic either, doesn't burn oil/smoke. I guess I should test the compression of all cylinders and see if they are low?

Thanks.

Matt

 

I wouldn't say that you've damaged it, but you almost certainly have been causing it to wear quicker. If you do run a low temp stat, you can help minimize wear on bearings and the like by running a very light oil. What oil do you use?

If the engine sounds fine, pulls good, and doesn't smoke -- don't worry about it. If you're not sure, a compression test would be a decent indicator of how well your rings are sealing, but won't tell you much else about wear in the engine. Do you have an oil pressure gauge? If not, install one. Low oil pressure is a good sign that you have excessive bearing wear.

 

Hey Matt I wouldn’t worry about it as long as you had some kind of stat in it. Ford listed a 160 and a 180 stat from ’58 to the early ‘70s and I don’t recall a rash of worn-out blocks. Just from experience I ran a smallblock with a 160 stat for over 200,000 miles and it only had .005” taper on the outside cylinders, even less on the inside ones. Relax, there are more important things to worry about.

Barry

[link:www.ford-trucks.com/guidelines.html | FTE Moderator]

 

I agree that the 160 won't hurt a thing. If you have to worry about the "lowest coeeficient of friction" of aluminum on the cast iron bores, you have some mighty big problems with your engine. On all engines, there is a coating of oil keeping the piston from actually touching the bore, same as the oil on the bearings. Granted the rings scrape the bore, but the oil lubricates them also. If you didn't have that coating of oil splashing on the bores, the softer aluminum piston would wear out in no time. Ever buy a performance chip? I put one in an 88 Bronco with a 302. It CAME with a 160 degree thermostat. Lower engine temp means more horsepower. That Bronco has been in the family since that chip and 160 were put in it. It's had well over a hundred thousand miles put on it since then, and that thing is still just as strong. I pulled the heads to do some port work, and there was no ridge what so ever. Uses no oil either. The biggest reason they started using higher temp thermostats was because of the pollutuion junk they started adding in the early 70's. It helped the engine produce fewer emissions. Just in case though, I used hypereutectic pistons with anti-friction coated skirts in my last engine. Between that and the synthetic oil, that engine will be around for a long, long time. 160 degree thermostat and all.

 

As I said, "don't worry about it" unless you are noticing performance problems. That said, though, I disagree with Steve's assertion that a 160 stat won't hurt a thing. In the long run, it will. How much it will hurt is a different question.

Ford has never specified a stat that low for the FE (or any other motor, as far as I know). Why? Because test after test over the century since internal combustion motors became common has shown that higher operating temps lead to less wear and longer engine life. The only reason they spec a 180 stat is that water, which makes an excellent coolant material due to its extremely high specific heat (plus the fact that it is cheap and plentiful) boils at 212. You need some margin for error. If water didn't boil until 300 degrees, we'd all be running 270 degree stats.

Also, cooler engine temp does not mean more power. A cooler intake charge is more dense, which means more air and fuel in the chamber and more power, but the cylinder itself should be HOT. Tests with exotic materials like ceramic blocks, heads and pistons that operate at temps close to 2,000 degrees have shown they generate awesome power. The ideal engine would be one with very high cylinder temps, but with the intake charge kept much cooler.