getting too hot!!!
- Thread starter 91whiteponygt
- Start date
RaceDvr50
New Member
But you see it's not a function of time because the coolant will be back in the radiator in a matter of seconds. It's purely a function of how many BTU's the radiator can exchange in total. The thermostat regulates the engine UP to a temperature not down to one. Try this experiment: Drop a thermostat into a pot of water and turn on the burner. Tell me at what point the thermostat starts to close again because it's too hot. I'll give you a hint, it never will. The thermostat will open wide and stay that way attemting to allow the radiator the chance to disperse the heat. I understand where you are coming from but the Physics don't work.
Perhaps you work on A/C a bit? This argument could be applied to A/C and it would make a lot more sense.
Check this link http://www.samarins.com/glossary/thermostat.html
Perhaps you work on A/C a bit? This argument could be applied to A/C and it would make a lot more sense.
Check this link http://www.samarins.com/glossary/thermostat.html
RaceDvr50
New Member
I'm saying that it is common knowledge that you can remove your stat and run your engine, assuming that you have no cooling problems before you do and you're engine will take a long time to warm up and never overheat. Common knowledge
You know what, never mind some people just will never get cars.
You know what, never mind some people just will never get cars.
WhiteFizzo
Founding Member
Have you checked the radiator itself? My brother-in-law had a 5.0 that wouldn't cool. I looked down into the top of the radiator, when the engine was cool of course, and you could see calicium deposits just lining everything. If someone put anything other than distilled water and antifreeze in there, you could have something similar. We changed the radiator, put new hoses and a new t-stat. After that, she ran cool.
GT_Rich
Member
Well, I'm at work too, and my books are at home. I don't have three years of physics, but I do have 5 years of engineering and now work for Goodrich Aerospace at their heating a specialty systems division.
Anyways, if you look at simple thermodynamics, it will yield the same answer whether there's a flow restriction or not. Just think about it:
mass flow rate*specific heat*change in temp*time=Q
(where Q is the cooling capability of the air flow over the radiator, which we have to assume constant for both cases)
If you slow down the flow rate but increase the time in the radiator, this equation will give you the same delta T.
HOWEVER, now think about the Log Mean Temperature Difference for heat exchangers. In it's rawest form, this equation [dT=(dT2-dT1)/ln(dT2-dT1)] neglects time and gives a theoretical answer for 100% heat transfer. Unfortunately, we don't have a perfect world and 100% heat transfer. Things such as contact resistance, disturbed air flow, etc all decrease the potential heat transfer of the heat exchanger. If you leave fluid in the radiator longer, it has a better chance of reaching a cooler temperature than more water flowing through faster. Remember, the best possible exit temperature of the water from the radiator is defined by the LMTD, but this needs time to get there.
Anyways, if you look at simple thermodynamics, it will yield the same answer whether there's a flow restriction or not. Just think about it:
mass flow rate*specific heat*change in temp*time=Q
(where Q is the cooling capability of the air flow over the radiator, which we have to assume constant for both cases)
If you slow down the flow rate but increase the time in the radiator, this equation will give you the same delta T.
HOWEVER, now think about the Log Mean Temperature Difference for heat exchangers. In it's rawest form, this equation [dT=(dT2-dT1)/ln(dT2-dT1)] neglects time and gives a theoretical answer for 100% heat transfer. Unfortunately, we don't have a perfect world and 100% heat transfer. Things such as contact resistance, disturbed air flow, etc all decrease the potential heat transfer of the heat exchanger. If you leave fluid in the radiator longer, it has a better chance of reaching a cooler temperature than more water flowing through faster. Remember, the best possible exit temperature of the water from the radiator is defined by the LMTD, but this needs time to get there.
RaceDvr50
New Member
I think you're fogetting that the radiator is a closed loop circuit and that the coolant will return in a matter of seconds. Yes the longer it stays in the radiator the more THAT coolant will decrease in temperature while the coolant in the engine absorbs more heat. Your logic isn't too bad bad not applicable to this situation. By the way my primary job is Laser technician so I do work with some reasonably serious cooling units.
I'd like one person who has this competely flawed concept stuck in their head to attempt to explain how after the thermostat opens all the way and the temperature continues to increase how the thermostat would then close a little to hold the coolant in the radiator longer. IT CAN'T, the hotter it gets the thermostat just opens up all the way and stays there.
I'm stating facts
By the way as far as the car goes you might have developed a blanket of cotton or debris between the A/C condenser and the radiator on the face of the radiator, you will probably need to move one or the other to see if this is the case. Often this will pass through the condenser and get stuck on the radiator.
I'd like one person who has this competely flawed concept stuck in their head to attempt to explain how after the thermostat opens all the way and the temperature continues to increase how the thermostat would then close a little to hold the coolant in the radiator longer. IT CAN'T, the hotter it gets the thermostat just opens up all the way and stays there.
I'm stating facts
By the way as far as the car goes you might have developed a blanket of cotton or debris between the A/C condenser and the radiator on the face of the radiator, you will probably need to move one or the other to see if this is the case. Often this will pass through the condenser and get stuck on the radiator.
Mavrick
Founding Member
RaceDvr50 said:
The slower the coolant flows through the rad, the cooler it gets. If coolant were flowing through the rad constantly at a high rate, then the rad wouldn't have enough time to do it's job proporly. Therefore the coolant would still be hot by the time it flows through the rad and back into the motor..
This would more than likely give your car a hard time when trying to warm up, but once it does get hot then it would have a much harder time cooling down to temp as the coolant is flowing through the rad way too fast.
Mavrick
Founding Member
RaceDvr50 said:
A 180* stat is supposed to start opening at 180*, correct? Therefore it would close, atleast partially, when coolant that is under 180* passes through the motor - until that coolant gets hotter than 180* where the stat would open again. This cycle repeats itself..
RaceDvr50
New Member
Mavrick said:
Once again for those of you who need a lesson in cooling. Thermal transfer is most efficient at a high temperature differential (FACT). You are not attempting to cool a specific volume of coolant until it reaches outside temperature. You are attempting to absorb heat from the engine, transfer it to the radiator and allow the radiator to disperse the heat. Does anybody here understand that the engine is still running? While that is occuring the coolant contained in the engine is absorbing heat. The FASTER you cycle the coolant through the radiator, the MORE total thermal transfer that we accomplish. I would prefer not to have to put this into an equation since most of you would not understand it anyway.
By the way, the thermostat can only start to close AFTER the temperature has dropped slightly. Try to explain how it would do it if the temperature was already high because of a load (i.e. pass down the track). It couldn't and if it worked that way things like my ultra high flow reverse opening thermostat would be pointless thus nobody would make them.
GT_Rich
Member
Yes it's closed loop, but will it actually return in a matter of seconds? The thermostat will open once temps reach 180 (as an example) and cooler than 180 fluid will come from the radiator, through the block, and back to the thermostat. If, when this fluid gets back to the thermostat, its temperature is still less than 180, the thermostat will CLOSE. Now, the fluid in the radiator (which was the hot fluid from the block) has time to cool. During this cooling time, the fluid in the block is going to heat up to 180 and the thermostat is going to open again. And the cycle repeats, each time allowing fluid in the block to heat up and fluid in the radiator to cool down. This should show up on your temp gauge as a needle bouncing above and below you thermostat set-point.
The system will go to a constant loop if the outside temp is hot enough (or the radiator is in poor enough of a condition) for the fluid from the radiator to the block to not be cool enough to stay below 180 by the time it gets through the block and to the thermostat. If it's above 180, then it will be constantly flowing, and no different than having no thermostat at all.
Now, with a thermostat that actually cycles open and close, TIME is a factor, and yes, having a thermostat can increase cooling ability.
Well this thread has turned into a monster 
I didn't find anything in the Atomotive Engineering Texts that I have. They don't even mention calculating the minimum flow rates for a cooling system. 3 SAE books on how to design engines and only minimal mention of a water pump.
So I went to the internet and found this...
http://www.arrowheadradiator.com
Check out Improvement Rule Number 1.
Basically this illustrates that as coolant flow rates increase, coolant temps will decrease. This is until the point of cavitation, excessive turbulence, and such. This source specifically states that time is not a factor in how well the radiator will function. (I am still trying to soak this in)
I have been assuming that unrestricted coolant flow would result in higher temps because of insufficient coolant time in the radiator. It would appear that the real cause of higher temps in these situations is poor flow characteristics.
So, I think the next question is...
What coolant flow rates can the windsor based motors handle?
How would we determine that?
Do we care?
Judge for yourself, and let the real debate begin
jason
Coolant Flow Rate
Looking at the previous expression, we can see that slowing the coolant down is the wrong way to go. If the heat load is constant, lowering the flow will increase the temperature drop through the radiator, making the bottom tank, or radiator outlet, temperature less than before. If the bottom tank temperature goes down, the top tank temperature must go up to maintain approximately the same average core temperature so that the heat load may be transferred to the cooling air. At the reduced power setting it would rise above 190 degrees F and at 240 hp the engine would be overheating worse than before. In fact, because the lower flow rate results in lower coolant velocity and less “scrubbing action” in the tubes, the average coolant temperature must rise slightly in order to transfer the heat load from the coolant to the cooling air, making matters even worse.
What would happen if we increase the coolant flow? Will it go through the radiator so fast that there won’t be time for cooling to take place? Not at all, from the expression, we can see that if the heat load is constant, increasing the coolant flow rate will reduce the coolant temperature drop through the radiator, resulting in a higher bottom tank temperature. If the bottom tank temperature is increased, the top tank temperature must go down to maintain approximately the same average core temperature. This is what we were hoping to achieve. With the top tank temperature now less that 190 degrees F at the reduced power point, we can expect that the system will be better able to run at 240 hp without overheating, In fact, because the increased coolant flow rate results in a higher coolant flow velocity and better “scrubbing action” in the tubes, the average coolant temperature decreases slightly while transferring the same heat load to the cooling air, further lowering the top tank temperature, resulting in better cooling performance.
From this we see that increasing the coolant flow rate will result in better heat transfer performance. There are some cautions to be observed in increasing coolant flow rate, however. Going too far may result in aeration and foaming of the coolant, possible damage to the radiator by overpressure, cavitation of the pump, due to excessive pressure drop through the radiator, and erosion of the radiator tubes. The ideal coolant flow rate is one that will provide optimum coolant flow velocity through the radiator tubes in the range of 6 to 8 feet per second. Flow velocities above 10 feet per second should be avoided.
[FONT=arial,arial,helvetica]Anything you can do to increase the coolant flow rate, within limits described, will improve heat transfer and cooling performance. Anything you do to restrict or reduce the coolant flow rate will hurt cooling performance[/FONT]
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[/FONT]
I didn't find anything in the Atomotive Engineering Texts that I have. They don't even mention calculating the minimum flow rates for a cooling system. 3 SAE books on how to design engines and only minimal mention of a water pump.
So I went to the internet and found this...
http://www.arrowheadradiator.com
Check out Improvement Rule Number 1.
Basically this illustrates that as coolant flow rates increase, coolant temps will decrease. This is until the point of cavitation, excessive turbulence, and such. This source specifically states that time is not a factor in how well the radiator will function. (I am still trying to soak this in)
I have been assuming that unrestricted coolant flow would result in higher temps because of insufficient coolant time in the radiator. It would appear that the real cause of higher temps in these situations is poor flow characteristics.
So, I think the next question is...
What coolant flow rates can the windsor based motors handle?
How would we determine that?
Do we care?
Judge for yourself, and let the real debate begin
jason
Coolant Flow Rate
Looking at the previous expression, we can see that slowing the coolant down is the wrong way to go. If the heat load is constant, lowering the flow will increase the temperature drop through the radiator, making the bottom tank, or radiator outlet, temperature less than before. If the bottom tank temperature goes down, the top tank temperature must go up to maintain approximately the same average core temperature so that the heat load may be transferred to the cooling air. At the reduced power setting it would rise above 190 degrees F and at 240 hp the engine would be overheating worse than before. In fact, because the lower flow rate results in lower coolant velocity and less “scrubbing action” in the tubes, the average coolant temperature must rise slightly in order to transfer the heat load from the coolant to the cooling air, making matters even worse.
What would happen if we increase the coolant flow? Will it go through the radiator so fast that there won’t be time for cooling to take place? Not at all, from the expression, we can see that if the heat load is constant, increasing the coolant flow rate will reduce the coolant temperature drop through the radiator, resulting in a higher bottom tank temperature. If the bottom tank temperature is increased, the top tank temperature must go down to maintain approximately the same average core temperature. This is what we were hoping to achieve. With the top tank temperature now less that 190 degrees F at the reduced power point, we can expect that the system will be better able to run at 240 hp without overheating, In fact, because the increased coolant flow rate results in a higher coolant flow velocity and better “scrubbing action” in the tubes, the average coolant temperature decreases slightly while transferring the same heat load to the cooling air, further lowering the top tank temperature, resulting in better cooling performance.
From this we see that increasing the coolant flow rate will result in better heat transfer performance. There are some cautions to be observed in increasing coolant flow rate, however. Going too far may result in aeration and foaming of the coolant, possible damage to the radiator by overpressure, cavitation of the pump, due to excessive pressure drop through the radiator, and erosion of the radiator tubes. The ideal coolant flow rate is one that will provide optimum coolant flow velocity through the radiator tubes in the range of 6 to 8 feet per second. Flow velocities above 10 feet per second should be avoided.
[FONT=arial,arial,helvetica]
- IMPROVEMENT RULE # 1 -
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RaceDvr50
New Member
GT_Rich said:
Yes the coolant returns in seconds! The flow capacity of your water pump is what?? Like 40 gallons per minute or something and your cooling system holds what 3 gallons? So without restriction you could cycle that coolant through the engine 13.3 times a minute with those numbers or that means the coolant would be back in 4.5 seconds.
P.S. See vristang's post, I believe he found somewhere that explained it better than I apparently could and I think he gets it now.
RaceDvr50
New Member
vristang said:Well this thread has turned into a monster
I didn't find anything in the Atomotive Engineering Texts that I have. They don't even mention calculating the minimum flow rates for a cooling system. 3 SAE books on how to design engines and only minimal mention of a water pump.
So I went to the internet and found this...
http://www.arrowheadradiator.com
Check out Improvement Rule Number 1.
Basically this illustrates that as coolant flow rates increase, coolant temps will decrease. This is until the point of cavitation, excessive turbulence, and such. This source specifically states that time is not a factor in how well the radiator will function. (I am still trying to soak this in)
I have been assuming that unrestricted coolant flow would result in higher temps because of insufficient coolant time in the radiator. It would appear that the real cause of higher temps in these situations is poor flow characteristics.
Thank you, this is basically the point I was trying to make higher coolant flow is a good thing. Simply a stuck open thermostat would not result in an overheat it would however slow down your warmup time.
RaceDvr50 said:
The point I was making was that higher coolant flow is better, to a point. At some point higher flow rates will cause more problems than benefits.
It appears that the problem with high flow rates is not due to limited cooling in the radiator, but rather due to flow characteristics.
We had 2 different points.
Moving on...
I am still trying to fully understand this. You said in an earlier post that your could express things in equation format.
Would you mind posting that?
It would help me a great deal.
Has anyone found any equation that relates radiator efficiencies to coolant flow rates?
Many thanks,
jason
91whiteponygt,
So did you figure out what is making you engine get hot and not want to cool down?
you asked about a thermostatic fan clutch?
Frequently Asked Questions from the Hayden Automotice Site:
FAN CLUTCHES
Q. How do I know if my fan clutch needs to be replaced?
A. These are the most common symptoms of a failed fan clutch:
Leaking fluid - Oily build up around the bearing or thermal spring.
Bad bearing - Seized, turns rough or has excessive play (more than 1/4" at fan tip).
Worn thermal spring - Spring is loose.
Some fan clutches will show no visible indication of a problem yet may still be faulty. The following may also indicate a faulty fan clutch:
Fan spins excessively - Three or more times when hot engine is shut off.
Poor air conditioning - At low speed or excessive high side pressures.
Doesn't engage - Fan speed does not increase or "locks up" when the engine is hot.
Does not disengage - Fan clutch won't slow down when the engine is cold.
Q. At what temperatures do fan clutches engage?
A. Most fan clutches engage at about 170° F air temperature (about 180-190° F engine temperature). They reduce the temperature about 20° F before disengaging
As I understood from automotive class, the thermostat function was mainly to restrict or divert coolant flow through the radiator in order to raise the engine to operating temperature as quickly as possible.
After the thermostat opens, coolant is diverted through the radiator. It is then the job of the fan and radiator to maintain a relatively constant operating temperature.
One thing you may want to check is your ground wires. Missing ground wire tend to make the car run hotter. I recall a fix where one would actually slip a wire under the upper hose and into the coolant. One would then have to ground the other end of the wire. This was a fix recommended by Cadillac in the early 80's.
vristang,
Maximum cooling occurs when you have maximum coolant flow through the radiator.
Good Luck
So did you figure out what is making you engine get hot and not want to cool down?
you asked about a thermostatic fan clutch?
Frequently Asked Questions from the Hayden Automotice Site:
FAN CLUTCHES
Q. How do I know if my fan clutch needs to be replaced?
A. These are the most common symptoms of a failed fan clutch:
Leaking fluid - Oily build up around the bearing or thermal spring.
Bad bearing - Seized, turns rough or has excessive play (more than 1/4" at fan tip).
Worn thermal spring - Spring is loose.
Some fan clutches will show no visible indication of a problem yet may still be faulty. The following may also indicate a faulty fan clutch:
Fan spins excessively - Three or more times when hot engine is shut off.
Poor air conditioning - At low speed or excessive high side pressures.
Doesn't engage - Fan speed does not increase or "locks up" when the engine is hot.
Does not disengage - Fan clutch won't slow down when the engine is cold.
Q. At what temperatures do fan clutches engage?
A. Most fan clutches engage at about 170° F air temperature (about 180-190° F engine temperature). They reduce the temperature about 20° F before disengaging
As I understood from automotive class, the thermostat function was mainly to restrict or divert coolant flow through the radiator in order to raise the engine to operating temperature as quickly as possible.
After the thermostat opens, coolant is diverted through the radiator. It is then the job of the fan and radiator to maintain a relatively constant operating temperature.
One thing you may want to check is your ground wires. Missing ground wire tend to make the car run hotter. I recall a fix where one would actually slip a wire under the upper hose and into the coolant. One would then have to ground the other end of the wire. This was a fix recommended by Cadillac in the early 80's.
vristang,
Maximum cooling occurs when you have maximum coolant flow through the radiator.
Good Luck
RaceDvr50 - Just taking some classes in physics doesn't mean you know everything about the t-stat. I have took three years of spanish, but I'm not going to try my luck at Mexico.
It is not a good idea to not have a t-stat. If you sit in traffic, the radiator is not being used so to speak. The coolant will flow in and out and not have time to be in a "cool" radiator...the temps will slowly rise, and overheat.
It is not a good idea to not have a t-stat. If you sit in traffic, the radiator is not being used so to speak. The coolant will flow in and out and not have time to be in a "cool" radiator...the temps will slowly rise, and overheat.
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