What does a automotive thermostat do?

I say it is a device that determines if the coolant in the motor is routed through the radiator or not and will bring the coolant to operating temperature.

Once it does that, its job is done. Should the coolant temperature drop below the rating of the thermostat, it wakes up and by routing the coolant away from the radiator, the temperature of coolant will again rise to the rating of the thermostat, and again it will route the coolant through the radiator.

Now here is the kicker. It has absolutely no control over the temperature rising and sometimes rise to overheating.

Just like the thermostat in your house, if you set it on heat at 68F, the house temperature will not go below, 68F. It has no control in how hot your house can get.

If you set the AC to 68F, the house temperature will not get hotter than 68F, but the house temperature can drop below freezing.

It only works in one temperature direction.

What say ye?

Sounds bout right to me. Just a heat activated valve, basically, right?

Yeah , but when it sticks open or shut the temp will go to hell in a hand basket!!

idahovette said:

Yeah , but when it sticks open or shut the temp will go to hell in a hand basket!!

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Only if it sticks closed right? I have ran many times with no thermostat at all. Never overheated, but took longer to warm up.

They're not switches. The wax motor isn't instantaneous. So it varies the opening of the 'stat over a range of several degrees. So as the coolant temp gets hotter it opens more, as it cools it retracts. Obviously, once it's fully open there's nothing more it can do to control temperature.

Arkansas_V8 said:

Only if it sticks closed right? I have ran many times with no thermostat at all. Never overheated, but took longer to warm up.

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I've found without one the water pump circulates the water too fast not allowing the coolant enough time in the radiator to cool it. Then eventually caused it to overheat. I'm not saying it happens to every car or truck but, I have seen happen to some of them. They're a cheap and easy part to change so I don't see a benefit in not having one. I think the difference between the temps on them is how much they open and control the rate of flow thru the radiator and motor.

Running a washer in the absence of a thermostat is said to help with coolant speed, but I’m not sure why you wouldn’t want a tstat. Probably harder to find the right size washer than a thermostat. Maybe for drag racing. But they’re running e-pumps a lot now and can probably dial the speed in on them.

My preference is a 195. Not because I know why, but that’s what the general specd for my engine. I guess for better economy...

I used to run a 185 in the 327.

82sbshortbed said:

I've found without one the water pump circulates the water too fast not allowing the coolant enough time in the radiator to cool it. Then eventually caused it to overheat. I'm not saying it happens to every car or truck but, I have seen happen to some of them. They're a cheap and easy part to change so I don't see a benefit in not having one. I think the difference between the temps on them is how much they open and control the rate of flow thru the radiator and motor.

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I had one fail closed on the trail. I removed it, and forgot about it.

Remembered in winter when it took longer to warm up, but I dont remember running my fans more without it.

But like you said every car is different.

82sbshortbed said:

I've found without one the water pump circulates the water too fast not allowing the coolant enough time in the radiator to cool it. Then eventually caused it to overheat. I'm not saying it happens to every car or truck but, I have seen happen to some of them. They're a cheap and easy part to change so I don't see a benefit in not having one. I think the difference between the temps on them is how much they open and control the rate of flow thru the radiator and motor.

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I'm no engineer, but if its flowing faster through the radiator and doesn't have enough time to sufficiently cool, wouldn't that also mean its spending less time in the block to heat up?

And as far as the flow capabilities of the water pump go, is a fully open thermostat really much of a restriction compared to not having one?

I've always thought that "no thermostat can cause overheating" was just a theory and it's never been proven. Or has it?

bucket said:

I'm no engineer, but if its flowing faster through the radiator and doesn't have enough time to sufficiently cool, wouldn't that also mean its spending less time in the block to heat up?

And as far as the flow capabilities of the water pump go, is a fully open thermostat really much of a restriction compared to not having one?

I've always thought that "no thermostat can cause overheating" was just a theory and it's never been proven. Or has it?

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Don't know about not having one, but do know that an aftermarket one on a '79 RamCharger I had would cause am overheat condition on the gauge but no real overheat.

Put an OE thermostat in, and the problem went away with no other changes made.

Flow rate issue , I assume .

What does everyone like to run and why? I.e. 195, 185, 175 etc.

Frankenchevy said:

What does everyone like to run and why? I.e. 195, 185, 175 etc.

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I prefer a 180 (Houston, TX = more summer than winter) but put what I assumed was the factory 195 with the 4 core .

Hoping for a factory flow rate match.

Even if that old 77 Suburban I had came with a 195 I don't ever remember seeing it go above a 1/4 on the gauge .

This one goes up to about 3/8's and then the stat opens and it drops.

Highest I have seen it is about 2 needle widths past the quarter mark .

The second mark from the left on the gauge.

Frankenchevy said:

What does everyone like to run and why? I.e. 195, 185, 175 etc.

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carbureted 180 , fuel injected 195 , that's what the factory specs usually.

bucket said:

I've always thought that "no thermostat can cause overheating" was just a theory and it's never been proven. Or has it?

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We would takes the guts out of a thermostat and use just the flat section with the hole in it for our racecars. That plate would serve as the proper restriction.

A thermostat has no control over engine overheating. It just controls the minimum temperature. See my original post.

Goldie Driver said:

I prefer a 180 (Houston, TX = more summer than winter) but put what I assumed was the factory 195 with the 4 core .

Hoping for a factory flow rate match.

Even if that old 77 Suburban I had came with a 195 I don't ever remember seeing it go above a 1/4 on the gauge .

This one goes up to about 3/8's and then the stat opens and it drops.

Highest I have seen it is about 2 needle widths past the quarter mark .

The second mark from the left on the gauge.

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I also run a 180. Shortish winters here in Arkansas. Mainly wanna keep her cool on the rocks, and in the mud.