Thoughts on installing a 'cooler' thermostat...???
07-27-2009, 03:53 PM
#31
Burning Brakes
From http://www.aa1car.com/library/overheat.htm "If the thermostat needs to be replaced, install one with the same temperature rating as the original. Most cars and light trucks since 1971 require thermostats with 192 or 195 degree ratings. Using a cooler thermostat (160 or 180) in an attempt to "cure" a tendency to overheat can increase fuel and oil consumption, ring wear and emissions. On newer vehicles with computerized engine controls, the wrong thermostat can prevent the computer system from going into closed loop resulting in major performance and emission problems if the engine fails to reach its normal operating temperature."
The easily observed fact that the coolant temp DOES rise on a hotter day with lower air flow, proves that, at that point the T-stat is full open. This does not happenin the middle of winter, yett he coolant temp is still the same for normal, in motion, operation. Physics dictates that the T-stat can not be full open under those circumstances. You can increase the cooling capacity of a radiator (remove heat from the coolant) in pretty much only a few ways. 1. Increase air flow. 2. Cooler inlet air flow 3. Coolant that has a better heat transfer characteristic. 4. Slow down the coolant flow through the radiator. The problem with #4 is that it is a closed loop sytem, so while the delta T will be lower at the radiator outlet, as 1999 states, the coolant may also pick up too much engine heat, thereby raising the inlet temp, or worse, boiling the coolant in the coolant passages and cause hydrolock. In general, higher flow through the system regualtes temperature better (reduce time of coolant control loop). I predict that in the near future we will see most cars go to electric coolant pumps that vary speed to load & heat inlet/outlet. I'm really surprised it hasn't happened already.
The easily observed fact that the coolant temp DOES rise on a hotter day with lower air flow, proves that, at that point the T-stat is full open. This does not happenin the middle of winter, yett he coolant temp is still the same for normal, in motion, operation. Physics dictates that the T-stat can not be full open under those circumstances. You can increase the cooling capacity of a radiator (remove heat from the coolant) in pretty much only a few ways. 1. Increase air flow. 2. Cooler inlet air flow 3. Coolant that has a better heat transfer characteristic. 4. Slow down the coolant flow through the radiator. The problem with #4 is that it is a closed loop sytem, so while the delta T will be lower at the radiator outlet, as 1999 states, the coolant may also pick up too much engine heat, thereby raising the inlet temp, or worse, boiling the coolant in the coolant passages and cause hydrolock. In general, higher flow through the system regualtes temperature better (reduce time of coolant control loop). I predict that in the near future we will see most cars go to electric coolant pumps that vary speed to load & heat inlet/outlet. I'm really surprised it hasn't happened already.
07-27-2009, 04:05 PM
#32
Drifting
Thread Starter
Sounds like hodgepodge references from printed material that has been partially memorized for a test - not totally unfactual or wholly inaccurate, but a lot of uneccessary fill. Bottom line is that a 160 degree t-stat will keep a 996 running cooler while underway. BTW: what is your reference to the objection to my 996 t-stat numbers before. I want to look them over pls.
From http://www.aa1car.com/library/overheat.htm "If the thermostat needs to be replaced, install one with the same temperature rating as the original. Most cars and light trucks since 1971 require thermostats with 192 or 195 degree ratings. Using a cooler thermostat (160 or 180) in an attempt to "cure" a tendency to overheat can increase fuel and oil consumption, ring wear and emissions. On newer vehicles with computerized engine controls, the wrong thermostat can prevent the computer system from going into closed loop resulting in major performance and emission problems if the engine fails to reach its normal operating temperature."
The easily observed fact that the coolant temp DOES rise on a hotter day with lower air flow, proves that, at that point the T-stat is full open. This does not happenin the middle of winter, yett he coolant temp is still the same for normal, in motion, operation. Physics dictates that the T-stat can not be full open under those circumstances. You can increase the cooling capacity of a radiator (remove heat from the coolant) in pretty much only a few ways. 1. Increase air flow. 2. Cooler inlet air flow 3. Coolant that has a better heat transfer characteristic. 4. Slow down the coolant flow through the radiator. The problem with #4 is that it is a closed loop sytem, so while the delta T will be lower at the radiator outlet, as 1999 states, the coolant may also pick up too much engine heat, thereby raising the inlet temp, or worse, boiling the coolant in the coolant passages and cause hydrolock. In general, higher flow through the system regualtes temperature better (reduce time of coolant control loop). I predict that in the near future we will see most cars go to electric coolant pumps that vary speed to load & heat inlet/outlet. I'm really surprised it hasn't happened already.
The easily observed fact that the coolant temp DOES rise on a hotter day with lower air flow, proves that, at that point the T-stat is full open. This does not happenin the middle of winter, yett he coolant temp is still the same for normal, in motion, operation. Physics dictates that the T-stat can not be full open under those circumstances. You can increase the cooling capacity of a radiator (remove heat from the coolant) in pretty much only a few ways. 1. Increase air flow. 2. Cooler inlet air flow 3. Coolant that has a better heat transfer characteristic. 4. Slow down the coolant flow through the radiator. The problem with #4 is that it is a closed loop sytem, so while the delta T will be lower at the radiator outlet, as 1999 states, the coolant may also pick up too much engine heat, thereby raising the inlet temp, or worse, boiling the coolant in the coolant passages and cause hydrolock. In general, higher flow through the system regualtes temperature better (reduce time of coolant control loop). I predict that in the near future we will see most cars go to electric coolant pumps that vary speed to load & heat inlet/outlet. I'm really surprised it hasn't happened already.
07-27-2009, 04:09 PM
#33
Instructor
Some cars run cooler without the thermostat and some run hotter. The reason there is a change is because you have removed the restriction of the thermostat from the flow path. There is an optimum speed at which the coolant should flow. Too slow and it absorbs too much heat. Too fast and the radiators have less time to cool it.
The purpose of the thermostat is to let the engine get to operating temperature as quickly as possible.
07-27-2009, 04:09 PM
#34
Race Car
Every car/truck will reach, lets say, 180 degrees in 0 degree weather just as it will in 120 degree weather.
So, to say once your t-stat is open (180 degrees) the cooling system is running at 100% duty is simply not true.
If that was the case, your car would overheat in the 100 degree weather since it was at 100% duty in the 0 degree temps.
T-stats do fluctuate flow for regulating coolant temps.
So, to say once your t-stat is open (180 degrees) the cooling system is running at 100% duty is simply not true.
If that was the case, your car would overheat in the 100 degree weather since it was at 100% duty in the 0 degree temps.
T-stats do fluctuate flow for regulating coolant temps.
Even at 70 mph without a thermostat and ambient temps of 10F, I have never seen my coolant drop below 185F.
Just install a lower t-stat and you'll see you still will get temps above 210F. Your temps can get that high even without a thermostat.
07-27-2009, 04:13 PM
#35
Drifting
Thread Starter
Probably because the 996 standard cooling system with the 2 little heat exchangers are on the hairy edge of efficiency. Typical Porshce engineering to shave toleranaces so close - has it's good points and bad points.
That assumes that the engine temperature is at or slightly above the t-stat specs and that the cooling stystem has the ability to offset any additional heat gain. In the case iof Porsche's t-stat, it is not except under specific conditions. If your engine is running at 200F which is far in excess of the openning of the t-stat, there is no variable control of the coolant flow by the stat..
Even at 70 mph without a thermostat and ambient temps of 10F, I have never seen my coolant drop below 185F.
Even at 70 mph without a thermostat and ambient temps of 10F, I have never seen my coolant drop below 185F.
07-27-2009, 04:16 PM
#36
Race Car
The thermostat effects flow because of the space it takes up. In the old days when thermostats were removed, you often had to install a specific size washer on the inlet to reduce the amount of flow.
07-27-2009, 04:24 PM
#37
Instructor
Putting a lower thermostat does nothing...unless your goal is to run the car cooler than the open point of the thermostat (184 deg or whatever it is).
So above 184 deg -> it's all about the driving speed, the number of radiators, coolant ratio, and lastly when the fans turn on.
If you want to modify anything here, I'd hack the fans so turn on earlier (aka manual switch or temperature sensor).
Below 184 degrees -> It's all about driving speed, engine RPM, ambient temperature etc...since no coolant is flowing.
The only remote possibility is the 184 deg stock thermostat is the flow restrictor in the coolant system and the 160 deg thermostat flows better removing this restriction....however at this point a "better flowing" 184 deg thermostat would do the same thing.
Hope this makes sense.
So above 184 deg -> it's all about the driving speed, the number of radiators, coolant ratio, and lastly when the fans turn on.
If you want to modify anything here, I'd hack the fans so turn on earlier (aka manual switch or temperature sensor).
Below 184 degrees -> It's all about driving speed, engine RPM, ambient temperature etc...since no coolant is flowing.
The only remote possibility is the 184 deg stock thermostat is the flow restrictor in the coolant system and the 160 deg thermostat flows better removing this restriction....however at this point a "better flowing" 184 deg thermostat would do the same thing.
Hope this makes sense.
07-27-2009, 04:29 PM
#38
Race Car
That assumes that the engine temperature is at or slightly above the t-stat specs and that the cooling system has the ability to offset any additional heat gain. In the case of Porsche's t-stat, it is not, except under specific conditions. If your engine is running at 200F which is far in excess of the opening of the t-stat, there is no variable control of the coolant flow by the stat..
Even at 70 mph without a thermostat and ambient temps of 10F, I have never seen my coolant drop below 185F.
Just install a lower t-stat and you'll see you still will get temps above 210F. Your temps can get that high even without a thermostat.
Even at 70 mph without a thermostat and ambient temps of 10F, I have never seen my coolant drop below 185F.
Just install a lower t-stat and you'll see you still will get temps above 210F. Your temps can get that high even without a thermostat.
07-27-2009, 04:40 PM
#39
Race Car
20 degrees less than what and under what conditions. I guarantee you that a mod consisting of only a themostat temperature change will not reduce temps by 20F from the target of 194F or even from 200F even if the ALMIGHTY himself made that claim. It's comparatively easy to reduce temps from 220 down to 200.
07-27-2009, 04:59 PM
#40
Race Car
I know it is very hard to believe but the t-stat opens and closes depending on coolant temp. If it cools enough, the t-stat can actually restrict coolant flow to maintain operating temps.
If my car, and like Robin said, maintained the same temps in both ends of the temperature spectrum (cold vs hot), proves it just doesnt open all the way and the engine coolant temps are solely at the mercy of the cooling systems total cooling ability.
If all the t-stat would do is open all the way, how in the world could your car maintain the same temperature in different temps? It wouldnt.
Forget stop and go. Mine would get hot too in both temp ranges if there wasnt sufficient airflow.
The t-stat opens and closes to regulate temp. That is its job. Warm up is just the beginning.
If my car, and like Robin said, maintained the same temps in both ends of the temperature spectrum (cold vs hot), proves it just doesnt open all the way and the engine coolant temps are solely at the mercy of the cooling systems total cooling ability.
If all the t-stat would do is open all the way, how in the world could your car maintain the same temperature in different temps? It wouldnt.
Forget stop and go. Mine would get hot too in both temp ranges if there wasnt sufficient airflow.
The t-stat opens and closes to regulate temp. That is its job. Warm up is just the beginning.
07-27-2009, 05:22 PM
#41
Race Car
I know it is very hard to believe but the t-stat opens and closes depending on coolant temp. If it cools enough, the t-stat can actually restrict coolant flow to maintain operating temps.
If my car, and like Robin said, maintained the same temps in both ends of the temperature spectrum (cold vs hot), proves it just doesnt open all the way and the engine coolant temps are solely at the mercy of the cooling systems total cooling ability.
If all the t-stat would do is open all the way, how in the world could your car maintain the same temperature in different temps? It wouldnt.
Forget stop and go. Mine would get hot too in both temp ranges if there wasnt sufficient airflow.
The t-stat opens and closes to regulate temp. That is its job. Warm up is just the beginning.
If my car, and like Robin said, maintained the same temps in both ends of the temperature spectrum (cold vs hot), proves it just doesnt open all the way and the engine coolant temps are solely at the mercy of the cooling systems total cooling ability.
If all the t-stat would do is open all the way, how in the world could your car maintain the same temperature in different temps? It wouldnt.
Forget stop and go. Mine would get hot too in both temp ranges if there wasnt sufficient airflow.
The t-stat opens and closes to regulate temp. That is its job. Warm up is just the beginning.
If your engne temperature is 193F your thermostat is not opening and closing. That is a fact. It dioes not operated on the bubble. Pull it out of your car and test it. We're not talking theory here, but real world operation. Better yet, remove it and drive your car then come back and report to us that you see the same high and cool coolant temps, then explain to us how that is possible.
Your thermostat is fully open and changes in temps results from many other conditions such as engine load, car speed, engine speed, ambient temps, sun or clouds; any of which will dramtically effect temperature. If the only variable that is changed is the point at which the thermostat opens, this is not and cannot be any change in coolant temperatures, just a change in the time it take to reach the same temperature.
The stock stat on the 996 will not close again once it is open except under very specific conditions. The engine is just too hot to begin with and the cooling system is too inefficient.
07-27-2009, 05:35 PM
#42
Drifting
Thread Starter
+1
I know it is very hard to believe but the t-stat opens and closes depending on coolant temp. If it cools enough, the t-stat can actually restrict coolant flow to maintain operating temps.
If my car, and like Robin said, maintained the same temps in both ends of the temperature spectrum (cold vs hot), proves it just doesnt open all the way and the engine coolant temps are solely at the mercy of the cooling systems total cooling ability.
If all the t-stat would do is open all the way, how in the world could your car maintain the same temperature in different temps? It wouldnt.
Forget stop and go. Mine would get hot too in both temp ranges if there wasnt sufficient airflow.
The t-stat opens and closes to regulate temp. That is its job. Warm up is just the beginning.
If my car, and like Robin said, maintained the same temps in both ends of the temperature spectrum (cold vs hot), proves it just doesnt open all the way and the engine coolant temps are solely at the mercy of the cooling systems total cooling ability.
If all the t-stat would do is open all the way, how in the world could your car maintain the same temperature in different temps? It wouldnt.
Forget stop and go. Mine would get hot too in both temp ranges if there wasnt sufficient airflow.
The t-stat opens and closes to regulate temp. That is its job. Warm up is just the beginning.
07-27-2009, 06:10 PM
#43
Race Car
The t-stat opening and closing.
I did the washer thing on my '69 Camaro. I 100% agree. You dont know what temp you will get unless you run it.
Peace out, Ive got better things to do.
07-27-2009, 06:34 PM
#44
Race Car
Once again, how does operating temp maintain in 0 degrees outside temps or 100 degrees outside temps?
The t-stat opening and closing.
I did the washer thing on my '69 Camaro. I 100% agree. You dont know what temp you will get unless you run it.
Peace out, Ive got better things to do.
The t-stat opening and closing.
I did the washer thing on my '69 Camaro. I 100% agree. You dont know what temp you will get unless you run it.
Peace out, Ive got better things to do.
07-27-2009, 07:09 PM
#45
Drifting
Thread Starter
A water cooled engine operating w/o a t-stat will seek temperature equilibrium based on engine heat generation (combustion, exhaust flow, etc) against it's ability to shed the same thru the radiator efficiency, flow and characteristics of the coolant and/or antifreeze qualities, wind thru the engine bay, other quantifiable intangibles (auto transmission cooled by engine radiator, etc.), etc. If the cooling system is up to it and there is good fresh air exchange happening in the engine bay, it will run very cool, maybe too cold even. Would be interesting to see what the 996 cooling system is 'up to'. My guess is that without the ability to enrgizethe cooling fans on before 210 degress, it might run 10-15 degrees cooler while the car is in motion. All in all, the 996 cooling systems sucks bad -- blows bad -- or ever how you want to characterize it. In my estimation these engines slowly cook themselves to death after they are shutdown. Too bad the aux cooling fans come on so 'late' - I think it would help if they came on about 20 - 25 degrees earlier - might help lower the initial hot soak cycle. Also need a post-shutdown electric circulator to flow the coolant thru the system to reduce hot soak badness. tsk -tsk...
I still intend to try a cooler t-stat and will report my observations.
I still intend to try a cooler t-stat and will report my observations.