When will replacing a thermostat improve cooling?

[Boo Boo Foo]

You're making a huge assumption that it is necessary for the fluid to remain in the radiator the same amount of time or longer in order to dissipate more heat than it can absorb in the block.

Yep, that's exactly what I'm saying and thank you for proving my point (albeit unknowingly).

As I mentioned before, you have to consider the types of materials involved in the heat exchanges. Aluminum and copper are better conductors of heat than iron, therefore the coolant can dissipate more heat quicker than than it collects in the block.

Exactly. Remember the two pivotal factors involved in the physics of heat exchange - initial temperature difference, and length of exposure. The FLAW in your logic is that the engine block is NEVER going to cool down while there's still fuel burning. Hence, the goal of the coolant system is to avoid stagnation within the block. Yes, cast iron retains immense heat while aluminum cools quickly - but that has little to do with coolant per se. The coolant is merely the conductive device needed to transfer that heat between the engine block and the radiator. The quicker the coolant can get from the block to the radiator the better, not the other way around.

The thing that counts here is that the engine block is essentially a furnace, that is, it ain't gonna stop trying to melt until the fuel stops burning. Hence, the goal of the coolant system is to offset the melting process (aka overheating). By extension, the coolant system is a bleeding system - it's role is to provide a constant source of energy escape. And THAT is the flaw in the theory of "dwell time"... if you allow coolant to stay in the engine block for too long under high workload, the coolant gains in temperature and in doing so, reduces it's ability to act as a heat sink.

The slowness of iron to radiate heat is also it's worst enemy in an overheating situation - that is, it also reflects the ability of iron to retain heat as well. Ergo, the goal is LOTS of coolant, and the lower the temperature of that coolant, the greater the benefits. Ironically, by trying to argue with physics, you've actually proven my point. The issue regarding a thermostat in the context of THIS particular thread relates to the role it plays - and my position is this... a thermostat's job is NOT to prevent overheating, rather, it is to prevent overcooling by arbitrarily imposing restriction into the coolant flow. In short, the only way an engine can overheat without a thermostat in place is because the coolant system is flawed to begin with. That's my point here. People keep mixing up the two systems - the goal of coolant system is to prevent overheating. The goal of a thermostat is to prevent overcooling. It's impossible for the latter to affect the former if the former is working functionally.

In fact, since iron is a poorer conductor of heat than aluminum (or copper), then the coolant could spend approximately 3x the amount of time in the block than would be necessary for it to cool in the radiator.

And THAT, right there, is rubbish. The coolant/block membrane is where the heat transfer takes place, and the longer the coolant stays still, the greater it heats up, and by extension, the less it does it's job. Ergo, the block overheats. The role of the coolant system is to provide a heat sink, a constant bleed of energy. This is achieved by providing LOTS of cool water, and then moving it on as quickly as possible so that MORE cool water meets the heat exchange membrane. The moment you introduce coolant stagnation into a fully warmed up internal combustion engine, you introduce overheating issues - period. Coolness and Flowrate are the goals.

Of course, it's possible to OVERCOOL an engine by introducing too much coolant and flowrate. Hence, a thermostat modulates that latter problem.

 

[Boo Boo Foo]

And most respected engine builders agree with me too.

Check out this site by Stewart EMP Components regarding the myths contained within particular thread.

 

[65up2d8]

And most respected engine builders agree with me too.

Check out this site by Stewart EMP Components regarding the myths contained within particular thread.

The site that you linked seems to support your overall theory somewhat, but you must also take creedence of the following statements in that link:

"For applications requiring a thermostat to keep the engine at operating temperature, we recommend using a Stewart/Robertshaw high flow thermostat. This thermostat does not restrict flow when open. The Stewart/ Robertshaw thermostat enhances the performance of the cooling system, using any style of water pump. However, the Stewart Stage 1 high-flow water pump may require this thermostat to operate properly, and Stewart Stage 2, 3, and 4 water pumps simply will NOT operate with a regular thermostat because these pumps have no internal bypasses."

The above quote seemingly recognizes that some engines need a thermostat to operate in the correct temperature range while others may not. Anticipating your next argument, notice that the Stage 1 water pump needs a thermostat whereas the Stage 2, 3, and 4 water pumps do not. So, it does not follow that every engine/cooling system will benefit or even cool the same when there is less flow resistance. Noone introduced the variable (engineer speak ) that the system under consideration is an optimized cooling system that can handle substantial amounts of pressure and volume.

Also note this statement:

"Years ago, cars used low pressure radiator caps with upright-style radiators. At high RPM, the water pump pressure would overcome the radiator cap's rating and force coolant out, resulting in an overheated engine. Many enthusiasts mistakenly believed that these situations were caused because the coolant was flowing through the radiator so quickly, that it did not have time to cool. Using restrictors or slowing water pump speed prevented the coolant from being forced out, and allowed the engine to run cooler. However, cars built in the past thirty years have used cross flow radiators that position the radiator cap on the low pressure (suction) side of the system. This type of system does not subject the radiator cap to pressure from the water pump, so it benefits from maximizing coolant flow, not restricting it."

The last time I checked, Mustangs were made "years ago" with "low pressure radiator caps [and] with upright-style radiators." Therefore, it seems to me you certainly can't generalize based on the website you've selected. Granted, it says coolant flow rate is not the ultimate source of the overheating under certain conditions, which without a doubt supports your "theory", but what enthusiast on this site will sleep better knowing about your "theory" if more flow in their particular application happens to melt their engine? The site you have linked deals with modern cars and predominantly racecars; therefore, what works for those applications does not necessarily hold true for our applications.

Finally, note the following from the supposed gem of knowledge you have posted:

"cars built in the past thirty years have used cross flow radiators that position the radiator cap on the low pressure (suction) side of the system."

You are on the Classic Tech Forum, which means the cars discussed on this forum ARE, by definition, over thirty years old. There is no such thing as a crossflow radiator on a stock Classic Mustang that I am aware of, and the aftermarket, to my knowledge, does not even offer such a radiator that is designed to be a direct replacement for the radiator on a Classic Mustang. I am, however, quite aware of the fact that it is possible to convert to a cross flow raditor as others on the site have done, but it is not a direct replacement to my knowledge.

Bottom line: You can't engineer everything on paper; you say Dark Buddha's points only solidify your righteousness, but in fact, the "sources" you've selected don't necessarily support your position with respect to this subject.

 

[DarkBuddha]

This will be my last post on this subject. I understand your point of view, and I don't even think we disagree, but you are distorting statements for some unknown self-serving purpose.

First, I don't think anything I said possibly came close to arguing with physics. I certainly never asserted that the coolant should ever stagnate. So I think you apparently completely missed the point of my "rubbish" statement. My simple point is that it is possilbe for the coolant to flow through the block and spend more time in the block (if the coolant passages have more overall volume than the radiator) and still be cooled adequately by the radiator even though it spends less actual time in the radiator. This is because a radiator should conduct heat approx. 3x better than iron.

Oh, and be careful reading into things... Notice I was speaking strictly about time, not flow characteristics or rate. It is not necessary for a change in flow rate for the coolant to spend more time in the block. There simply has to be more coolant passage volume than radiator volume.

Going back to the original statements that started this thread (which is and always was my only concern), specifically as to whether removing a tstat could possibly contribute to an overheating situation, I have one question that keeps coming to mind: Is it possible (theoretically or in real world application) for coolant to flow through a block so quickly that it is not able to absorb heat from the block? I believe the answer is yes given that heat exchange does not happen instantaneously, but rather it happens over some amount of time. This may be completely "academic" and theoretical, but the moment we say that you know someone will have this exact problem. That said, I do think your comment about a tstat functioning to prevent overcooling is mostly accurate.

So, in conclusion, run a damn tstat... run one that is a bit below the overheating point for your engine (and maybe leave yourself some headroom), but high enough to keep the engine at an efficient heat level (for good combustion). 180* always worked pretty good for me.

 

[Boo Boo Foo]

...snip...

Going back to the original statements that started this thread (which is and always was my only concern), specifically as to whether removing a tstat could possibly contribute to an overheating situation, I have one question that keeps coming to mind: Is it possible (theoretically or in real world application) for coolant to flow through a block so quickly that it is not able to absorb heat from the block?

...snip...

I think the answer to that is effectively the same if we were to ask if it's theoretically possible to NOT die from hyperthermia if we were towed (at incredibly high speeds) through water as cold as the night of the Titanic disaster. The short answer is no. Surface tension between the cooler and hotter surfaces results in a medium for heat exchange regardless. Although, in the interests of fairness, it's worth noting that at ridiculously high speeds like a Space Shuttle orbital re-entry, friction can come into your calculations. But I doubt anyone will be pumping coolant through an engine block any time soon at 17,000 miles per hour.

...snip...

Finally, note the following from the supposed gem of knowledge you have posted...

...snip...

you can't engineer everything on paper; you say Dark Buddha's points only solidify your righteousness, but in fact, the "sources" you've selected don't necessarily support your position with respect to this subject.

Interesting display of projection there - namely, accusing the accused of being guilty of that which we ourselves are practising. Think about that.

You use the words "in fact", but at this point in time, I'm the only person who's bothered to provide a third party cite regarding this subject - accordingly, whatever.

 

[rbohm]

well all i can say is that in practical experience, you need a restrictor of some sort to help prevent overheating in most situations. back in the late 70's, when i was racing, i was helping a team that had problems with their racecar overheating. they tried everything, larger rads, higher flow pumps, lower flow, pumps, made sure the air could flow out of the engine compartment more efficiently than it came in, used an airdam to prevent backflow of air, NOTHING worked, untill we tried a flow restrictor with a 5/8" opening. viola problem solved. i have found this to be the case many many times with different race AND street cars. my own mustang had an overheating problem, untill i found that the tstat was gone. rpelaced it with a 180 stat, and problem solved. i have seen too many time where the simple addition of a stat to the system where one was removed, solve an overheating problem.

 

[6Stang7]

Contrary to popular belief, removing the thermostat completely or putting in a low temp thermostat will NOT cause your engine to overheat because "the coolant doesn't spend enough time in the radiator to cool down" due to the increased speed of circulation. By the same logic "the coolent also doesn't spend as much time in the engine to heat up".

let me refer to to a post i made in another thread.

let me refer you to Newton's Law of Cooling, which can be expressed as a differential equation.

(dT/dt)=k[T-T(s)]

where k is a constant, T is the initial temp. T(s) is the cooler temp. make a simple change of variable y(t)=T(t)-T(s). Since T(s) is a constant, you get y'(t)=T'(t) making the equation:
(dy/dt)=ky

so, the equation works as:
T(t)=T(s)+[T-T(s)]e^(kt)
k is still a constant and t is time.

now let me put this is simple terms since some people will not understand this.

the faster the coolant moves through the radiator, the less time it has contact with that cooler surface. look at the equation is red. an increase in time will result in a lower temp. more over, your idea that the coolant would then spend less time in the block, therefore not receive as much heat is flawed to a point. you are right that the coolant wont take on as much heat, but this is to a point. since the coolant wont remove as much heat, or energy, from the block, that means that the temp of the block will get higher because more and more energy is added to it. now, look at the equation is red again and instead of cooling, look at as a heating function (your k should now be positive where as it is negative in a cooling function). the larger difference in temp between the coolant and engine means less time is required to transfer the same amount of energy. now, wait, there will be large temp difference between the coolant and the cooler radiator, so shouldn’t it all work out? no. the radiator has A LOT less surface area then the engine block, which means there is less energy transfer.

 

[6Stang7]

Going back to the original statements that started this thread (which is and always was my only concern), specifically as to whether removing a tstat could possibly contribute to an overheating situation, I have one question that keeps coming to mind: Is it possible (theoretically or in real world application) for coolant to flow through a block so quickly that it is not able to absorb heat from the block? I believe the answer is yes given that heat exchange does not happen instantaneously, but rather it happens over some amount of time. This may be completely "academic" and theoretical, but the moment we say that you know someone will have this exact problem. That said, I do think your comment about a tstat functioning to prevent overcooling is mostly accurate

remember though, if the coolant doesnt receive the heat, then the block holds on to it. this means the block will get to a higher temp. the large the temp difference between to objects (in this case, the block and the coolant) the more energy that can be transferred in the same amount of time if the difference was less.

 

[6Stang7]

Yes, everything that 70NitrousEater and Boo Boo Foo said is 100% correct.

Edit: I'm not going to even try to explain in my own words. I think the logic has already been laid out very clearly. If you don't get it, I'm not going to be able to help.

ok, then argue against mathmatics.

 

[Route666]

I agree with this statement...somewhat. BUT, look at it in regards to a car that's about to overheat. Even tho there is no thermostat in place, the temperature of the coolant is still 200* or more, thus your arguments about delta T are not relevant. Delta T is going to get as high as absolutely possible before the engine actually overheats. That's one of the reasons I'm saying that removing the thermostat won't cause it to overheat.

What follows is how I thought about it, and the last one how I came around that I was wrong.

Example - radiator is WAY too small, without tstat

coolant goes to engine, gets warm
goes to radiator, doesn't lose much energy
engine now hotter, coolant gets warmer
goes to radiator, loses only a little more than last time
engine now even hotter, coolant gets warmer
etc.

Now imagine this engine with a thermostat, there would be a slow but cooler stream coming into the engine all the time, and the radiator would be working more efficiently since the coolant is so hot in the radiator.

The trouble is, the non-thermo'd one's radiator would work as efficienty at the same radiator temperature, which, with faster flow rate would probably be cooler engine temperature than the one slowing flower (lol I actually typed that) I mean flowing slower PLUS the coolant is flowing faster so if the engine WAS overheating WITH the tstat, the radiator would have a constant flow of hotter water than if it was slower and had a chance to cool down, and so would remove more heat (per unit time) than if it had a Tstat.

Yes I definitely agree that removing a tstat will NOT cause an engine to overheat, and in fact would almost certainly increase the cooling system's efficiency.

I guess that's why they sell high flow water pumps.

 

[r x F]

Is it possible (theoretically or in real world application) for coolant to flow through a block so quickly that it is not able to absorb heat from the block? I believe the answer is yes given that heat exchange does not happen instantaneously, but rather it happens over some amount of time.

Wrong. See my original post.
There can be reasons that too much flow could cause overheating: cavitation, running on the bad side of the pump curve, over pressurizing the radiator cap on a down-flow radiator, etc...
Overheating because the coolant doesn't have "time" to absorb the heat is not true. Ask any engineer.

 

[Max Power]

I can't read physics. My brain doesn't work that say. Must have been the bloodletting.

Do any of these formulas account for the 1/3rd of engine heat that leaves through the exhaust, and how other engine modifications can effect that rate?

 

[68torino]

Well 70_Nitrous_Eater you made your points and I made mine. I think I only disagreed with one. Been interesting but I see it got 'hijacked' by people arguing theory and such.
Catch ya next time, kudos to you for keeping it polite

 

[10secgoal]

I'm sorry you think I'm ignorant 10secondgoal,

Eh ? You'll have to find me a quote or something. I don't remember that part. If you are reffering to my intelligence or ignorance comment, I think you miss understood it. I was poking at torino. One side of the room here is wrong, and from all the the posts I have read here, I certainly don't think the side that is wrong is unintelligance. Just igorance. Ignorance is just not knowing any better. Over time I think it has turned more into an insult because of the missuse of the word. ( Because of that person's ignorance.)
They has been no stone throwing here. I am glad to see we can argue here maturely unlike the rest of this website.

 

[r x F]

I also don't see how you can say that the dwell time is a wifes tale.

One side of the room here is wrong, and from all the the posts I have read here, I certainly don't think the side that is wrong is unintelligance. Just igorance. Ignorance is just not knowing any better.

What part of my first post do you disagree with?

 

[68torino]

Eh ? You'll have to find me a quote or something. I don't remember that part. If you are reffering to my intelligence or ignorance comment, I think you miss understood it. I was poking at torino. One side of the room here is wrong, and from all the the posts I have read here, I certainly don't think the side that is wrong is unintelligance. Just igorance. Ignorance is just not knowing any better. Over time I think it has turned more into an insult because of the missuse of the word. ( Because of that person's ignorance.)
They has been no stone throwing here. I am glad to see we can argue here maturely unlike the rest of this website.

10secgoal you have it right. Ignorance is simply not knowing. Unintelligence places is a dig against the ability to learn. I was making said dig but should not have. Otherwise poke away, did not mind a bit. Poking and digs are here to get us to think not react post.

 

[6Stang7]

I can't read physics. My brain doesn't work that say. Must have been the bloodletting.

Do any of these formulas account for the 1/3rd of engine heat that leaves through the exhaust, and how other engine modifications can effect that rate?

i assume you are referring to this equation
T(t)=T(s)+[T-T(s)]e^(kt)


and it's irrelevant with this formula. all this formula models is that the transfer of energy. in other words, the transfer of the heat from the block to the coolant, and then the coolant to the radiator. yes 1/3 of the heat goes out in exhaust, so 2/3 are being transferred into the block, which intern goes to the coolant. the initial temp would just be that 2/3's heat.


More over, those of you that can’t understand the equation; let me ask you this. If you cant understand how the equation is working, then how can you fully understand if a flow of coolant restricted to a point will or will not improve cooling? If you don’t understand the equation, then one can infer that you don’t understand everything that is going on. If you don’t understand everything that is going on, how can you come to a correct conclusion?

The link that was posted to that NASCAR site which said un-restricted flow is better is deceiving. Remember, this is under RACE APPLICATIONS! These are motors which are seeing around 8K-9K in RPM, and air running across the radiator at over 170mph. this doesn’t in anyway help understand how a normal car will function.

i'm going to work out a simple example using the equation in the hopes that it will help some of you understand how it functions.

 

[10secgoal]

What part of my first post do you disagree with?

I wouldn't say I disagree, as much to say I didn't understand it. If you'da caught me about 7 years ago, my ADD might not have been so bad and I would have tried to figure out your post.
I still can't say for sure that anyone is dead wrong. I think there are too many variables. But I just can't ignore that fact that the longer two unalike temps are together, the closer it becomes to a medium. ( Dwell in the radiator.) Whether it because of a different t-stat or bigger radiator. Will a bigger radiator dissipate more heat ? Yes. Longer surface are to cool, AND more time on the radiator, because it must travel farther. And the farther down the line to coolant moves, lower the temp will be, because the first part of radiator does most of the work. But if a radiator holds lets say 4 gallons of coolant, and every 20 seconds has to give up 25% to the motor, is going to fair better than a 2 gallon radiator that has to give up the same 1 gallon. It has less time to cool the same amount of coolant. Now if you keep it in there longer, you can gain the same objective. The cooler the coolant is by the time the motor needs it ( the better job the radiator does), the slower the motor needs it, because it will take longer for the motor to heat the coolant up to the medium (thermostat degree). Granted the lower coolant temp will rise exponentially faster towards the medium, but the higher temp to begin, will reach it first. SO, if motor has a thermostat at 190, the water temp exiting the motor will be higher than the water temp exiting a motor with a 160 thermostat , right ? So the water entering at a higher temp will lower faster. And the lower temp will not go plummeting towards ambient like the hotter coolant. So by sticking a higher thermostat in, you are spreading the difference in degrees of heat ( and in return, stay in the motor and radiator longer to reject heat). And putting in a smaller one, you are bringing it closer to ambient air, and will not cool as fast (comparably speaking). So a smaller thermostat does need a better cooling system. Otherwise the coolant enters the motor only a few degrees below the thermostat, and is immidiately sent back out to be cooled. This continues until the thersatat stays open constantly, waiting for that cool water temp to enter the motor, but never does. And slowly starts to overheat.
I think I have confused myself now. Time to nap.

 

[6Stang7]

Ok, here is a simple example of this cooling function I posted.

Now let’s say you removed a pizza from the oven, and the temperature of the pizza at this time is 185°F. You set the pizza on a table where the room temperature is 75°F. After one ½ hour the pizza is 150°F. What is the temperature after ¾’s of an hour? When will the pizza reach 100°F?

First, let’s sort out what information we need, and what information we have. Let’s look at the equation T(t)=T(s)+[T-T(s)]e^(kt)
T=initial temperature=185°F
T(s)=cooler temperature=75°F
t=time
k=some constant
e=an irrational number (like pi) which≈2.71.

Now, we do not know the constant k, so let’s first solve that. We are going to use the given information that after one ½ hour, the pizza is 150°F. So, let’s plug that information in the equation.
T=185°F
T(s)=75°F
t=30 minutes ( i am going to solve the equation in terms of minutes, but I could use ½ if I wanted to solve in terms of hours)

So, we take T(t)=T(s)+[T-T(s)]e^(kt), and plug in or numbers and get:
150=75+(185-75)e^(30k)

Subtract 75 from both sides, and subtract 75 from 185 and we get:

110e^(30k)=75

Divide both sides but 110 to get:

e^(30k)=(75/110)

now, to bring the exponent of 30k down, we will take the natural log (ln) of e. ln(e^x)=x so when we take the natural log we get:

30k=ln(75/110)

Divide both sides by 30 and we now have what our constant is:

k=[ln(75/110)]/30 ≈-.012766, however, we will leave it in the form of k=[ln(75/110)]/30 to get a closer answer.

So, now that we have solved k, our equation is now:
T(t)= 75+(185-75)e^({[ln(75/110)]/30}t)

Now, to answer the question of what temperature the pizza will be after ¾’s of an hour, or 45 mins. To solve this, we plug in 45 for our t to get:

75+(185-75)e^({[ln(75/110)]/30}45)
Now just plug this into a calculator and we get:136.9292118, or about 137. so, after 45 mins the pizza is 137°F

Now, let’s answer when the pizza will reach 100°F. To solve this, we will set the eqation equal to 100 and solve for t. So we get:

75+(185-75)e^({[ln(75/110)]/30}t)=100

Subtract 75 from both sides to and 75 from 185 get:

(110)e^({[ln(75/110)]/30}t)=25

Now divide both sides by 110 to get:

e^({[ln(75/110)]/30}t)=(25/110)

Now we will take the natural log of both sides to get:

{[ln(75/110)]/30}t=ln(25/110)

Now, divide both sides by {[ln(75/110)]/30} to get:

t=[ ln(25/110)]/{[ln(75/110)]/30}

Plug this into your calculator and we get:116.0549227 or about 116 mins. So in 116 mins, the pizza will reach 100°F.


Heating problems work in the same way, except that your k will be a positive instead of the negative it is in a cooling function.

 

[10secgoal]

More over, those of you that can’t understand the equation; let me ask you this. If you cant understand how the equation is working, then how can you fully understand if a flow of coolant restricted to a point will or will not improve cooling? If you don’t understand the equation, then one can infer that you don’t understand everything that is going on. If you don’t understand everything that is going on, how can you come to a correct conclusion?


i'm going to work out a simple example using the equation in the hopes that it will help some of you understand how it functions.

Nope, don't understand it. But that does not mean us that do not understand the math don't know what's going on. Math is short hand for all the crap I just typed. If I just typed all that in Spanish would you have understood it ? But you would has still understood what's going on, even though you didn't understand me, right ? Let's remember that equations come from ideas. They are ideas put into mathmatical form. Not understanding the mathmatics, does not mean you don't understand the idea. I have put 'er down so most can understand. If you want people to understand your idea, so we see it from your POV, maybe the math needs to go.