Low temp thermostat, coolant temp variation
04-02-2013, 02:23 PM
#1
Low temp thermostat, coolant temp variation
So I fitted the above the weekend, and I have noticed that when driving the temp gauge gets close to 180, then is slowly drops around 15 degrees and goes back up, this cycles a few times. I presume that it’s the thermostat opening and closing as it is warming up. I never noticed this on the previous std thermostat (but then I probably wasn’t watching as closely). I seem to remember the std stat getting to just over 180 and staying there.
Is this normal for the low temp stat?, I hope to take the car on a longer run to see if the temp stabilizes, as at the moment have only done short trips
Is this normal for the low temp stat?, I hope to take the car on a longer run to see if the temp stabilizes, as at the moment have only done short trips
04-02-2013, 02:37 PM
#2
That's my experience also and your explanation makes sense. I think that's also why it's better - the engine now spends more time (on avg) at the lower end of the temp range.
I also noticed:
- the SAI pump kicks in more frequently during the morning drive when car is not fully warmed up yet
- the alternator voltage stays a little higher on avg (due to now a little lower engine temp. The alternator regulator compensates for temp - lower the temp, higher the voltage output).
- no change in mpg the way I'm driving (mainly local)
I also noticed:
- the SAI pump kicks in more frequently during the morning drive when car is not fully warmed up yet
- the alternator voltage stays a little higher on avg (due to now a little lower engine temp. The alternator regulator compensates for temp - lower the temp, higher the voltage output).
- no change in mpg the way I'm driving (mainly local)
04-02-2013, 03:09 PM
#4
Race Director
That's my experience also and your explanation makes sense. I think that's also why it's better - the engine now spends more time (on avg) at the lower end of the temp range.
I also noticed:
- the SAI pump kicks in more frequently during the morning drive when car is not fully warmed up yet
- the alternator voltage stays a little higher on avg (due to now a little lower engine temp. The alternator regulator compensates for temp - lower the temp, higher the voltage output).
- no change in mpg the way I'm driving (mainly local)
I also noticed:
- the SAI pump kicks in more frequently during the morning drive when car is not fully warmed up yet
- the alternator voltage stays a little higher on avg (due to now a little lower engine temp. The alternator regulator compensates for temp - lower the temp, higher the voltage output).
- no change in mpg the way I'm driving (mainly local)
The t-stat opening/closing means the engine experiences repeated expansion/contraction cycles, albeit small, but over time will probably have the head gaskets leaking.
There's an increased in risk the t-stat will fail due to mechanical fatigue from the repeated cycling it goes through.
The lower engine temp means the engine is being fed a richer mixture than it would be otherwise. While the car's mileage hasn't appeared to be affected -- though upon closer examination it will be found to have been affected -- the cooler engine with the richer mixture is generating a lot more unburned gas and water build up in the oil.
To make matters worse since the engine runs cooler the oil will not get hot enough to boil this away and the build up will probably require more frequent oil/filters services.
The SAI coming on while driving means the converters are cold and the engine controller concurrently with the SAI coming on is adding even more fuel so the injected air will burn post the combustion chambers and heat the converters to their necessary temperature.
The alternator is working harder and this can only shorten its life.
All to run the engine cooler where wear is increased.
Better?
I don't think so.
04-02-2013, 03:16 PM
#5
I have read several older arguments for and against using the lower temp T-stat but I wonder what the latest real world research / testing shows. Didn't JR even recommend the lower T-stat? Has anyone got the latest scoop?
04-02-2013, 03:57 PM
#6
You have a twisted definition of "better".
The t-stat opening/closing means the engine experiences repeated expansion/contraction cycles, albeit small, but over time will probably have the head gaskets leaking.
There's an increased in risk the t-stat will fail due to mechanical fatigue from the repeated cycling it goes through.
The lower engine temp means the engine is being fed a richer mixture than it would be otherwise. While the car's mileage hasn't appeared to be affected -- though upon closer examination it will be found to have been affected -- the cooler engine with the richer mixture is generating a lot more unburned gas and water build up in the oil.
To make matters worse since the engine runs cooler the oil will not get hot enough to boil this away and the build up will probably require more frequent oil/filters services.
The SAI coming on while driving means the converters are cold and the engine controller concurrently with the SAI coming on is adding even more fuel so the injected air will burn post the combustion chambers and heat the converters to their necessary temperature.
The alternator is working harder and this can only shorten its life.
All to run the engine cooler where wear is increased.
Better?
I don't think so.
The t-stat opening/closing means the engine experiences repeated expansion/contraction cycles, albeit small, but over time will probably have the head gaskets leaking.
There's an increased in risk the t-stat will fail due to mechanical fatigue from the repeated cycling it goes through.
The lower engine temp means the engine is being fed a richer mixture than it would be otherwise. While the car's mileage hasn't appeared to be affected -- though upon closer examination it will be found to have been affected -- the cooler engine with the richer mixture is generating a lot more unburned gas and water build up in the oil.
To make matters worse since the engine runs cooler the oil will not get hot enough to boil this away and the build up will probably require more frequent oil/filters services.
The SAI coming on while driving means the converters are cold and the engine controller concurrently with the SAI coming on is adding even more fuel so the injected air will burn post the combustion chambers and heat the converters to their necessary temperature.
The alternator is working harder and this can only shorten its life.
All to run the engine cooler where wear is increased.
Better?
I don't think so.
The alternator at a higher voltage means it charges the battery faster. I always think the temperature compensation of the regulator is flawed on our cars since it's detecing the engine compartment temperature as opposed to the battery temperature. For a front engine car where the alternator and battery lie in the same compartment, that works well but not on our car. I always feel like our battery is a little undercharged compared to other cars because of this compensation.
I've read both Hartech (http://www.hartech.org/docs/buyers%2...20part%205.pdf) and Jake's articles and happen to be a convert on this one at least...
Oh btw, I'll do a UOA in 2k miles (first one after the low-temp thermostat install) so let's see if we see any trend there.
Last edited by Ahsai; 04-02-2013 at 04:16 PM.
04-02-2013, 04:19 PM
#7
We are all using modern synthetic oils, right?
The lower temp thing I think is more personal decision and psychologically more comforting to some people that the needle is closer to the middle. Gotta wonder how many people would be less inclined to do this if Porsche had calibrated their gauge to read more inline with traditional car gauges where middle means you're a-ok and not cold like the Porsche gauges. My $.02.
I think if you hook up a water temp gauge to other cars besides Porsche, you'll find that 180deg isn't really that hot or dangerous in any way and is inline with where other cars are running more or less.
The lower temp thing I think is more personal decision and psychologically more comforting to some people that the needle is closer to the middle. Gotta wonder how many people would be less inclined to do this if Porsche had calibrated their gauge to read more inline with traditional car gauges where middle means you're a-ok and not cold like the Porsche gauges. My $.02.
I think if you hook up a water temp gauge to other cars besides Porsche, you'll find that 180deg isn't really that hot or dangerous in any way and is inline with where other cars are running more or less.
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04-02-2013, 04:22 PM
#8
We are all using modern synthetic oils, right?
The lower temp thing I think is more personal decision and psychologically more comforting to some people that the needle is closer to the middle. Gotta wonder how many people would be less inclined to do this if Porsche had calibrated their gauge to read more inline with traditional car gauges where middle means you're a-ok and not cold like the Porsche gauges. My $.02.
I think if you hook up a water temp gauge to other cars besides Porsche, you'll find that 180deg isn't really that hot or dangerous in any way and is inline with where other cars are running more or less.
The lower temp thing I think is more personal decision and psychologically more comforting to some people that the needle is closer to the middle. Gotta wonder how many people would be less inclined to do this if Porsche had calibrated their gauge to read more inline with traditional car gauges where middle means you're a-ok and not cold like the Porsche gauges. My $.02.
I think if you hook up a water temp gauge to other cars besides Porsche, you'll find that 180deg isn't really that hot or dangerous in any way and is inline with where other cars are running more or less.
04-02-2013, 04:31 PM
#9
It's funny how we pick apart Porsche(maybe a snowball witch hunt from the IMS?) and try to re-engineer everything. I'm sure there are some improvements that can be made and some of them could be detrimental. However I also see several high mileage examples that have done just fine driving it as is the way it came from Stuttgart. That's my story and I'm sticking to it. I don't like to have stained lips from drinking Kool-aid.
Seems like the Porsche crowd sometimes wants that last 5-10% regardless just to have a peace of mind or some sense of security sometimes.
I'll side with the Porsche engineers on this one as if it was something they really felt was wrong to begin with, they would've changed it on their later models at least with no additional cost to them(just different spec t-stat).
Seems like the Porsche crowd sometimes wants that last 5-10% regardless just to have a peace of mind or some sense of security sometimes.
I'll side with the Porsche engineers on this one as if it was something they really felt was wrong to begin with, they would've changed it on their later models at least with no additional cost to them(just different spec t-stat).
04-02-2013, 05:33 PM
#11
Instructor
04-02-2013, 05:41 PM
#12
The reason for the standard high temp thermostat is because of emmisions, to control emmissions, you need a hot running engine. So the T stat decision is not made by Porsche for engine longevity, but to comply with emmissions.
Hartech recommends the low temp stat because there is one situation, although it doesn't happen all the time, that can hurt your motor. The t stat is at the end of the cooling system loop, so that water that hits the stat has already gone through the radiators and is at its coldest. Therefore, there is a lag time between the coolant in the motor heating up and the opening of the stat. The hot coolant has to go through the entire sytem, through the radiators, before it hits the stat and opens it.
So in a situation where you are cruising along on the freeway at high speed, low rpms, the cooling system is at its most efficient. The OEM stat is partialy closed or closed completely, which means the coolant is not going through the rads. Now, you downshift a couple of gears and really get on the throttle, the temperature in the head instantaneously goes up, and since the OEM stat is closed, or partially closed, cold coolant does not get to the head, which can lead to local overheating, especially in the cylinders furthest from the WP. If you have a stat that keeps the coolant 20+ degrees cooler in that situation, you have a cushion and also the stat opens earlier, which allows coolant that has gone through the rads to get to the head sooner.
The cooler stat can't hurt anything, and it can help in some situations.
Hartech recommends the low temp stat because there is one situation, although it doesn't happen all the time, that can hurt your motor. The t stat is at the end of the cooling system loop, so that water that hits the stat has already gone through the radiators and is at its coldest. Therefore, there is a lag time between the coolant in the motor heating up and the opening of the stat. The hot coolant has to go through the entire sytem, through the radiators, before it hits the stat and opens it.
So in a situation where you are cruising along on the freeway at high speed, low rpms, the cooling system is at its most efficient. The OEM stat is partialy closed or closed completely, which means the coolant is not going through the rads. Now, you downshift a couple of gears and really get on the throttle, the temperature in the head instantaneously goes up, and since the OEM stat is closed, or partially closed, cold coolant does not get to the head, which can lead to local overheating, especially in the cylinders furthest from the WP. If you have a stat that keeps the coolant 20+ degrees cooler in that situation, you have a cushion and also the stat opens earlier, which allows coolant that has gone through the rads to get to the head sooner.
The cooler stat can't hurt anything, and it can help in some situations.
04-02-2013, 05:56 PM
#13
Rennlist Member
It's funny how we pick apart Porsche(maybe a snowball witch hunt from the IMS?) and try to re-engineer everything. I'm sure there are some improvements that can be made and some of them could be detrimental. However I also see several high mileage examples that have done just fine driving it as is the way it came from Stuttgart. That's my story and I'm sticking to it. I don't like to have stained lips from drinking Kool-aid.
Seems like the Porsche crowd sometimes wants that last 5-10% regardless just to have a peace of mind or some sense of security sometimes.
Seems like the Porsche crowd sometimes wants that last 5-10% regardless just to have a peace of mind or some sense of security sometimes.
04-02-2013, 05:56 PM
#14
The reason for the standard high temp thermostat is because of emmisions, to control emmissions, you need a hot running engine. So the T stat decision is not made by Porsche for engine longevity, but to comply with emmissions.
Hartech recommends the low temp stat because there is one situation, although it doesn't happen all the time, that can hurt your motor. The t stat is at the end of the cooling system loop, so that water that hits the stat has already gone through the radiators and is at its coldest. Therefore, there is a lag time between the coolant in the motor heating up and the opening of the stat. The hot coolant has to go through the entire sytem, through the radiators, before it hits the stat and opens it.
So in a situation where you are cruising along on the freeway at high speed, low rpms, the cooling system is at its most efficient. The OEM stat is partialy closed or closed completely, which means the coolant is not going through the rads. Now, you downshift a couple of gears and really get on the throttle, the temperature in the head instantaneously goes up, and since the OEM stat is closed, or partially closed, cold coolant does not get to the head, which can lead to local overheating, especially in the cylinders furthest from the WP. If you have a stat that keeps the coolant 20+ degrees cooler in that situation, you have a cushion and also the stat opens earlier, which allows coolant that has gone through the rads to get to the head sooner.
The cooler stat can't hurt anything, and it can help in some situations.
Hartech recommends the low temp stat because there is one situation, although it doesn't happen all the time, that can hurt your motor. The t stat is at the end of the cooling system loop, so that water that hits the stat has already gone through the radiators and is at its coldest. Therefore, there is a lag time between the coolant in the motor heating up and the opening of the stat. The hot coolant has to go through the entire sytem, through the radiators, before it hits the stat and opens it.
So in a situation where you are cruising along on the freeway at high speed, low rpms, the cooling system is at its most efficient. The OEM stat is partialy closed or closed completely, which means the coolant is not going through the rads. Now, you downshift a couple of gears and really get on the throttle, the temperature in the head instantaneously goes up, and since the OEM stat is closed, or partially closed, cold coolant does not get to the head, which can lead to local overheating, especially in the cylinders furthest from the WP. If you have a stat that keeps the coolant 20+ degrees cooler in that situation, you have a cushion and also the stat opens earlier, which allows coolant that has gone through the rads to get to the head sooner.
The cooler stat can't hurt anything, and it can help in some situations.
Nothing in life is guaranteed except death and taxes. Just drive it like you stole it, keep up regular maintenance, and enjoy the moment.
04-02-2013, 05:57 PM
#15
But whats really unusual and maybe a credit to Porsche's 996 coolant system design, is that my front rad fans rarely come on (with AC off of course) while stopped or driving yet I know they are working correctly. In fact, even though I am in a warm climate the cars temp never comes close to overheating.
I have done a complete coolant system flush and run Pentosin but I must admit I am very impressed with the systems effeciency to rid itself of the engines heat. Maybe they got this part right?
And, San you are correct. Pre super strict emission times, one of the first mods we did was a 160 T-stat.
I have done a complete coolant system flush and run Pentosin but I must admit I am very impressed with the systems effeciency to rid itself of the engines heat. Maybe they got this part right?
And, San you are correct. Pre super strict emission times, one of the first mods we did was a 160 T-stat.
Last edited by KrazyK; 04-02-2013 at 06:25 PM.