When will replacing a thermostat improve cooling?

ForceFed70 · Aug 1, 2005

D.Hearne said:
Oh, but it does......... It takes longer to remove the heat from the coolant than it does to put it there. The engine is always capable of producing heat faster than the radiator can remove it. The radiator size is a constant, the engine's ability to produce heat is not. If the coolant is hotter, then it's obviously removed more heat from the engine.

Now we're thinking!

It does not take "longer". The difference is in surface area and temperature difference between the heating/cooling object.

In some instances you may be correct... the engine could put out more heat than the radiator can cool. Which is why cars overheat.

BUT under normal circumastances and with a healthy cooling system, this does not happen. This is why top-speed runs are possible. True the engine is putting out a crapload of heat... but at the same time, the car is going very fast and thus there is alot of airflow through the radiator in order to remove that heat. Now we are getting into cooling system design.

For the sake of simplicity... pick a scenario... crusing down the street, idleing, top speed run, speeding up then slowing down, whatever. In every scenario, the same factors remain and the cooling system functions the same. The only difference is the amount of heat produced by the engine and the amount of airflow through the radiator.

D.Hearne · Aug 1, 2005

You're completely missing my point. It doesn't matter that the coolant spends equal time in the engine and the radiator, it STILL takes more time for the radiator to remove the heat from the coolant than it does for the engine to put it there. Otheriwise, why would the radiator have such small passages? If what you say was true, the engine would also have small passages to allow the coolant to absorb the heat. The surface area that the coolant comes into contact with in the radiator is much larger than in the engine.

68torino · Aug 1, 2005

70_Nitous_Eater you have also neglected to factor in amount of flow. if you have too much flow for the amount of heat a radiator can exchange than one minute of time gathering heat vs one minute of time trying to shed the heat in a radiator that cannot due to too much coolant flow = overheating. It is not JUST a FACTOR of TIME but is actually a factor of time, amount of flow, themo efficency of the cooling system(to include radiated heat from the motor)and amount of air flow through the cooling system. You could have the greatest cooling system in the world with no air flow and it won't cool enough.
A good example would be a person working outside in the heat. They overheat and jump into a pool. If they move around just right(flow+time) they will cool down nicely. If they sit in one place(time, but no flow) they will slowly begin to overheat. If they move around and have extra coolant(pool water) flow (time+flow+flow) they will overcool and get chilled. If they are swimming around vigorously they could go into overheat(time+flow-excess work generating heat).
And this doesn't even take into fact that some people have efficent thermostats(body temp regulation) or inefficent thermostats). At least with a car if you have a good cooling system you can help improve it with the correct thermostat.

ForceFed70 · Aug 1, 2005

D.Hearne said:
You're completely missing my point. It doesn't matter that the coolant spends equal time in the engine and the radiator, it STILL takes more time for the radiator to remove the heat from the coolant than it does for the engine to put it there. Otheriwise, why would the radiator have such small passages? If what you say was true, the engine would also have small passages to allow the coolant to absorb the heat. The surface area that the coolant comes into contact with in the radiator is much larger than in the engine.

You are absolutely correct. But what difference does this make? The reason that there arn't lots of tiny passages instead of a few larger ones is because there doesn't need to be. The difference in temp between the engine and the coolant is much greater than the difference in temp between the coolant and the ambient air temperature. This is why the radiator must have more surface area.

Now we're argueing the same point. My analogy was to show that the average time the coolant stays in the radiator is the same. Thus the "coolant doesn't have time to cool down enough" theory is incorrect. It spends the same amount of time there, just not as much time in any 1 pass.

The engine doesn't heat up "really fast" nor does the coolant. Otherwise when you start your engine in the winter, the car would be hot in a matter of seconds instead of minutes. This acts like a buffer in the cooling system. Allowing for short moments of excessive heating without adequate airflow to not overheat the system.

D.Hearne · Aug 1, 2005

70_Nitrous_Eater said:
Now we're thinking!
The only difference is the amount of heat produced by the engine and the amount of airflow through the radiator.

And that's where the T-stat comes into play. Remove it and you will upset the balance. If you had a constant speed application, and the cooling system was designed optimally, you could remove it, without causing a problem.

ForceFed70 · Aug 1, 2005

68torino said:
70_Nitous_Eater you have also neglected to factor in amount of flow. if you have too much flow for the amount of heat a radiator can exchange than one minute of time gathering heat vs one minute of time trying to shed the heat in a radiator that cannot due to too much coolant flow = overheating.

Again... this is a closed system... not just hot water running through a radiator and out the other side. Again, the radiator "radiates" the same amount of heat. This is heat removed from the engine. Flow only comes into play when there is too little of it...not when there is too much.

It is not JUST a FACTOR of TIME but is actually a factor of time, amount of flow, themo efficency of the cooling system(to include radiated heat from the motor)and amount of air flow through the cooling system. You could have the greatest cooling system in the world with no air flow and it won't cool enough.
A good example would be a person working outside in the heat. They overheat and jump into a pool. If they move around just right(flow+time) they will cool down nicely. If they sit in one place(time, but no flow) they will slow ly begin to overheat. If they move around and have extra coolant(pool water) flow (time+flow+flow) they will overcool and get chilled. If they are swimming around vigorously they could go into overheat(time+flow-excess work generating heat).
And this doesn't even take into fact that some people have efficent thermostats(body temp regulation) or inefficent thermostats). At least with a car if you have a good cooling system you can help improve it with the correct thermostat.

Radiated heat from an engine does not change with the speed of the coolant moving through the engine. So you can toss that factor out the window.

As for the pool analogy... it's great and all, and I agree to an extend.. it's nothing like the cooling system in a vehicle.

Remember we are dicsussing how having too much "flow" will cause your engine to overheat (which I say is false). But even in your example, you state that more flow is better.

Again.. I believe a thermostat is deginately there for a reason. My only point being that having no thermostat will not cause overheating. So far, everyone says it will because "the coolant doesn't spend enough time in the radiator to cool down properly" But I've just explained a few times now that the total time is the exact same.

68torino · Aug 1, 2005

Qoute by 70_Nitrous_Eater Now we're argueing the same point. My analogy was to show that the average time the coolant stays in the radiator is the same. Thus the "coolant doesn't have time to cool down enough" theory is incorrect. It spends the same amount of time there, just not as much time in any 1 pass.

But if you increase the volume or amount of coolant going thru the radiator by removing the thermostat(no restriction) this COULD overwhelm the ability of the radiator to extract enough heat. Which is why I advocate not removing the thermostat and not running a cooler stat in mid 80s and up small blocks and big blocks on computer controlled engines. And I don't say on all motors removing the stat will cause an overheating problem. I haveseen it enough on older systems to say ALWAYS run a stat. MY only blanket statement is I PREFER AND RECOMMEND a190*-195* stat in small blocks and big blocks. I haven't got burnt yet.

ForceFed70 · Aug 1, 2005

D.Hearne said:
And that's where the T-stat comes into play. Remove it and you will upset the balance. If you had a constant speed application, and the cooling system was designed optimally, you could remove it, without causing a problem.

Upset the ballance as in have the engine run too cool at times.

That asside... even in a constant speed application you could not removed the thermostat because the ambient air temperature changes. Thus effecting cooling.

ForceFed70 · Aug 1, 2005

68torino said:
But if you increase the volume or amount of coolant going thru the radiator by removing the thermostat(no restriction) this COULD overwhelm the ability of the radiator to extract enough heat. Which is why I advocate not removing the thermostat and not running a cooler stat in mid 80s and up small blocks and big blocks on computer controlled engines. And I don't say on all motors removing the stat will cause an overheating problem. I haveseen it enough on older systems to say ALWAYS run a stat. MY only blanket statement is I PREFER AND RECOMMEND a190*-195* stat in small blocks and big blocks. I haven't got burnt yet.

Explain to me how it could "overwhelm" the radiator.

Again this is a closed system. Heat removed by the radiator is heat generated by the engine. The amount of heat radiated is the same. The speed of the coolant through the radiator does not compromise efficiency.. the radiator still radiates the same amount of heat.

It comes down to Heat in = heat out. If the radiator is radiating xxx amount of heat, it doesn't matter what the flow rate is so long at it's enough to keep up with the amount of heat being created by the engine.

D.Hearne · Aug 1, 2005

70_Nitrous_Eater said:
Upset the ballance as in have the engine run too cool at times.

That asside... even in a constant speed application you could not removed the thermostat because the ambient air temperature changes. Thus effecting cooling.

Yea the ambient air temp changes, but not as much(or less) as the amount of heat the engine in a car is able to produce in operation.

pabear89 · Aug 1, 2005

The thermostat is there to control the engine temp as to getting it to max effic levels quicker.
And to provide Cabin heat without running for extended periods.

Remove the Stat, and it takes longer to bring entire coolant level to operating temps. And lower temps could do harm to the internals over extended use.

And I have seen non thermostated engines run Hot,
Try a long 70 mph highway run in 90* heat for about 100 miles..

PB

shotsy · Aug 1, 2005

Temp of the thermostat changes the <b>operating temp</b> of the motor in a corectly working cooling system. A 180 deg therm will run warmer than a car with a 160 deg therm Right!!, In both cases the therm has to be there to slow the flow through the radiator for optimum heat transfer. In a colder climate run the 180 in the hotter climate run the 160.

Max Power · Aug 1, 2005

70, you are working under the premise that the radiator dissapating heat is a fixed rate, regardless of flow. You are not taking into account that an engine could be designed to produce more heat that the radiator can eliminate is unrestricted.

Eliminating the restriction could result in the coolant reentering the engine 5 degrees hotter every lap, or round trip, resulting in overheating.

I don't know how to state it in engineering speak, but I have seen it in practice repeatedly. Come up with every theoretical that you want, it doesn't change what I have seen in 30 years of working on cars.

67coupe351w · Aug 1, 2005

I'd really like to see somoene do some experiments on paper for this. Heat transfer goes down as a function of Delta T so it would be interesting to see what you find out by doing some simple calculations (maybe not simple).

Max power - I don't think any manufacturer would produce a cooling package insufficiant for the engine. (at least for the hp rating you got it from them) We have a test group dedicated to cooling packages and they insure that the cooling packages with do their job.

I'm not tryin to flame you but it's those "Ive seen so-in-so for 30+++ years" statements that really show a person's inability to accept change. Look how medicine has changed over the years. I'm glad they still don't blood let because "thats how we've done it for 30 years". or how about we've used carbs for 30 years there's nothin better.

Stick to your guns nitrous eater, so far you havent had too much scientific backing to statements against you. I for one would like to see some -- in either direction.

Max Power · Aug 1, 2005

"Unrestricted", 67coupe351w. The sentance says, "unrestricted".

I have plenty ability to accept change. How, exactly, would you propose to change what I have seen in the past?

Your analogies about bloodletting are not only not applicable, they're outright absurd.

67coupe351w · Aug 1, 2005

Max Power said:
"Unrestricted", 67coupe351w. The sentance says, "unrestricted".

Ahh ya you did say unrestricted.

All I'm saying is this:

So far, for the most part, the aurguments are all based on opinion. People could aurgue an entire lifetime and never get anywhere that way...politics for example. I was just trying to come up with a way to put an end to the fight with some math.

10secgoal · Aug 1, 2005

I can tell you what I did, from experience. 110+ deg heat in the Mojave desert. x-303 cam in 302, 40 over with RPM heads. Too much heat from the motor for the rad. I knew the rad was too small so I tried a few things. I did remove the t-stat. Over heated. Took for ever and a day to come up to temp. Now, I have even tried it with the rad I have now, and the car wouldn't come up to temp without a t-stat. I was able to put a 160 in the car with the upgraded rad. For a band aid, I put in a 195 t-stat and cured the problem, until I put my foot in it. Now, I have seen a few points, but I think they all work together. Yes, a t-stat does control water temp. BUT, the adverse effect is that the water will absorb the heat from the motor faster if it's cooler. I thinks it is Boyles law, but don't quote me. I don't think I even spelled it right. Any ways, the farther away the temps are from each other, the faster it will transfer the heat. Hence, when you burn yourself, you put your hand under cold water. The point here is with a 160, the coolant will absorb the motor heat faster, and need to be removed sooner than with say, a 190.
Also, it does matter how long the water is in the rad. It is just lke an intercooler. You have to choose between a more restrictive one, for better heat transfer, compared to one that flows better, but doesn't cool as well.

Boo Boo Foo · Aug 2, 2005

68torino said:
<snip>

A good example would be a person working outside in the heat. They overheat and jump into a pool. If they move around just right(flow+time) they will cool down nicely. If they sit in one place(time, but no flow) they will slowly begin to overheat. If they move around and have extra coolant(pool water) flow (time+flow+flow) they will overcool and get chilled. If they are swimming around vigorously they could go into overheat(time+flow-excess work generating heat).

<snip>

OK... bolding mine... I came to this thread late, but if there's one thing I am an expert in, it's physics. Not necessarily all things Mustang, but Physics is definitely my bag. Hence, the bolding above is worth commenting on because it isn't exactly true. And here's why...

It's a fundamental law of physics that the rate of heat exchange between one medium and another is determined by the initial difference in temperature between those two mediums. In your example above, your assumption is that the pool water is initially quite high to begin with (which is not unfair seeing as how you did describe the day as being a hot one). However, consider the poor victims of the Titanic disaster who were thrown into the Atlantic after the ship sunk that night. The ambient water temperature that night was just 2C apparently, and as such, most of the victims died within 4 minutes - regardless of whether they tried to stay perfectly still. And the reason? The rate of heat exchange was incredibly great due to the permanent state of the ocean's temperature that night.

And my point? You can't have your cake and eat it too... if we agree that a thermostat restricts flow as an engine goes through it's warmup cycle, we can also agree that freeing up that restriction allows heat transfer to take place AFTER that restriction is removed. By extension, it's impossible to argue that freeing up that restriction EVEN MORE will somehow result in greater water temperatures once again. It isn't a parabolic graph with an ideal operating flow per minute area in the middle. Heat exchange is a function of exposure to cooler mediums - period. If there is a greater flowrate, greater amounts of coolant are being exposed to the radiator's cooler surfaces per given time frame. In short, radiator dwell time is an old wive's tale. An unimpeded coolant system exposes the ENTIRE coolant to an overall greater heat exchange, rather than just a PART of it.

The issues are maximum water pump flow rate, radiator efficiency, variable flow rate resistance, and most importantly, ambient air temperatures. The last two points are vitally important in the context of overheating. Essentially, in almost every American and European vehicle made since 1960, an unimpeded coolant system has almost always been capable of overcooling an engine unless the vehicle is driving around in Death Valley ambient temperatures. The assumption here is that the coolant system is perfectly healthy in all of it's parts. If that assumption is true, then the REAL role of a thermostat is actually to prevent overcooling, not overheating.

To that end, this is why modern Formula One cars overheat so quickly if they're sitting still on the grid for too long at the start of a race. The issue is not the thermostat, nor is it flow rate - rather, it's the fact that the still air in the radiator pods heats up to a point where vastly inefficient heat transfers are taking place.

Route666 · Aug 2, 2005

I've only read a couple of posts since mine, so I don't know what has been said, but here's my extra bit:

Nitrous, it CAN be worse because with a restriction the coolant can get hotter in the engine and cooler in the radiator, making the delta T when it reaches the engine or radiator greater than it would be if it were running around faster, and all lukewarm, thus energy transfer happens quicker and for longer.

Thus the system's ability to transmit energy is greater.

In the non-thermostat example the coolant temp might be higher coming out of the engine, but the radiator may not extract as much heat as it would with the coolant moving slower, so more energy goes back to the engine, less heat goes into the coolant from the engine because the coolant is already hotter, and heat death starts to happen.

It isn't as simple as your car will run hotter without a thermostat than it does with one, heck it might be cooler, in most or all circumstances, but the system will perform more effectively with one. So if you have a radiator that is too big already, aluminium, with magic non-aqueous propylene glycol coolant, etc, removing the thermostat may not cause your engine to run hotter. However, match that cooling system with an engine that can overpower it, and the thermostat'd system will be able to remove more energy at a higher rate than one without.

Route666 · Aug 2, 2005

70_Nitrous_Eater said:
The amount of time the coolant spends inside of the engine or inside of the radiator is not a consideration. It's the TEMPERATURE of the coolant that matters. True, having it sit in the rad longer will make the coolant drop in temp more...but having it sit in the engine longer will make it increase in temp more. You cannot have 1 without the other.

What you are overlooking here (I dunno if it's been pointed out yet) is that if at any point in time the same engine / cooling system combo without a Tstat had coolant in the engine at the same temperature as the combo WITH one, the coolant in the radiator spends less time in there, but is hotter. While a larger delta T transfers energy QUICKER, this rate still needs TIME to transfer a total amount of energy and if you reduce the amount of time the coolant spends in the radiator more than you increase the difference in temperature, the coolant will not shed as much energy as it might have moving slower and at a lower temp.

There could well be instances where removing the Tstat makes the engine run cooler, but it is also just as likely (moreso IMO based on the fact that people DESIGNED the tstat into the engine) that an engine without a Tstat will run hotter. Plus without a Tstat it takes longer to get the engine to operating temp.

When will replacing a thermostat improve cooling?

That's why they call it "dope"

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