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Well I replaced the 83 degree thermostat with a 71 degree version today and once again can confirm that the car just flat out runs cooler with the lower temp thermostat. 96 degrees out today and I drove around, boosted, went up and down hills, etc., and the car stayed pretty consistently just above the first (80 degree) line. With the 83 degree thermostat, it ran about 1/2 between the lines (and at times as much as 3/4). Go figure.
Not doubting you but this doesn’t make any sense, a thermostat has nothing to do with the upper temp an engine reaches. All a lower than stock thermostat will do is cause the engine not to reach optimum operating temperature.
Well, I know here in Texas I'll take whatever I can get to start the engine cooling sooner in the summer. If it is opening earlier and staying open throughout any variations in engine temp then (for me) that is a good thing.
Additionally, I removed my turbo thermostat (the PO had it in backwards) and that had a positive effect on my gauge staying down to the first mark. However, in the winter it really slows down warmup. I'd like to put the little thermostat back in and I guess the first test will be to put it in RIGHT and see where the temp gauge stays.
Not doubting you but this doesn’t make any sense, a thermostat has nothing to do with the upper temp an engine reaches. All a lower than stock thermostat will do is cause the engine not to reach optimum operating temperature.
I understand that logic, and it was compelling enough for me to try the 83 degree PCNA thermostat despite my prior experiences. However, there's clearly "something" going on that's not being factored in to that logic. There's no question my car runs cooler with the 71 degree thermostat. At least based on the dash gauge, I'd say the car runs about 10C above the thermostat ratings when the system is cooling to the lowest it allows. Not sure why that is -- I may drop the 83 degree version in a pot of water and see if it's fully open at 83, or just starting to open, or what. But on my car, with the 71 degree t-stat, the car sits just above the 80 degree first white mark; and with the 83 degree version it sits a little above half way between the lines which equates to a little above 90C. I think the missing link in the logic is that the temp rating of the thermostat does not represent the lowest stasis point it will create in the motor. Not sure what you consider optimal temp, but that low 80's range is good with me -- it's plenty warm for the engine management system, yet it gives me more room to deal with extra heat from a/c, boost runs, heavy traffic, etc.
Originally Posted by dme
Well, I know here in Texas I'll take whatever I can get to start the engine cooling sooner in the summer. If it is opening earlier and staying open throughout any variations in engine temp then (for me) that is a good thing.
Additionally, I removed my turbo thermostat (the PO had it in backwards) and that had a positive effect on my gauge staying down to the first mark. However, in the winter it really slows down warmup. I'd like to put the little thermostat back in and I guess the first test will be to put it in RIGHT and see where the temp gauge stays.
Try the 71 and report back. I think you'll like it, but maybe my car is just weird.
Great feedback Tom, thanks. This comes handy, as my new engine runs a little warmer, most likely because of the deck plate, and it seems I can't tune this out. I will therefore try a lower temp thermostat.
I understand that logic, and it was compelling enough for me to try the 83 degree PCNA thermostat despite my prior experiences. However, there's clearly "something" going on that's not being factored in to that logic. There's no question my car runs cooler with the 71 degree thermostat. At least based on the dash gauge, I'd say the car runs about 10C above the thermostat ratings when the system is cooling to the lowest it allows. Not sure why that is -- I may drop the 83 degree version in a pot of water and see if it's fully open at 83, or just starting to open, or what. But on my car, with the 71 degree t-stat, the car sits just above the 80 degree first white mark; and with the 83 degree version it sits a little above half way between the lines which equates to a little above 90C. I think the missing link in the logic is that the temp rating of the thermostat does not represent the lowest stasis point it will create in the motor. Not sure what you consider optimal temp, but that low 80's range is good with me -- it's plenty warm for the engine management system, yet it gives me more room to deal with extra heat from a/c, boost runs, heavy traffic, etc....
You have triggered my curiosity which may be a bad thing lol. Two questions iydm:
Did the fans cycle during your boosted spirited run after you changed the thermostat for a lower temp one, especially if you were stationary for any period during that time?
Thom -- worth a try. At least you'll find out if the thermostat is contributing to the higher temps you are seeing. Mine sure was -- see below.
Mike -- at first I was worried they wouldn't come on since they did not come on in the garage warming up the car. But after driving a while, including boost, etc., the fans were indeed running on low speed when I got back. I was a bit paranoid, because I removed the fans to get at the thermostat, and ended up "detailing" them while out -- so wanted to make sure I didn't screw anything up in the process. The fan switch is 85/93.
I had the old 71C Wahler t-stat from the water pump I just replaced, along with the almost-new 83 degree version, so I just put them in a pot of water and tried to monitor the temps when they opened etc. It was a pseudo scientific test insofar as it is hard to keep the water a uniform temp from top to bottom, but I did my best stirring and turning off the flame and not touching the probe to the pot, etc. Testing deficiencies aside, it sure seemed to show that these things START to open at the rated number. The 83C version (~181F) was only open about 1mm, if that, with a water temp around 83C, whereas the 71 degree version was fully open. Stove-top testing pretty much validates what I'm seeing in the car -- i.e., that the thermostat opens all the way, and the system finds its lowest cooling point (at least in hot weather), about 10C degrees above the rated temp of the thermostat. So, if you run an 83 degree thermostat, there's no mystery why the car wants to run closer to 93. Now, in much cooler weather, you could imagine the motor finding a lower running temp, since the cold air might allow the motor to stay cooler with the t-stat only partially open. But if you are in hotter weather and would prefer not to run in that 90-100C range all the time, I think it makes sense (in logic and practice) to jump down to the lower temp thermostat and fan switch.
Wanting to make sure I'm not crazy, I googled and found a Stat description that confirms exactly my findings. It says the rated temp is when the thermostat starts to open, and that it's not fully open until 15-20F (~8-11C) higher than the rated temp. How did I never know this?
...Mike -- at first I was worried they wouldn't come on since they did not come on in the garage warming up the car. But after driving a while, including boost, etc., the fans were indeed running on low speed when I got back. I was a bit paranoid, because I removed the fans to get at the thermostat, and ended up "detailing" them while out -- so wanted to make sure I didn't screw anything up in the process. The fan switch is 85/93.
I had the old 71C Wahler t-stat from the water pump I just replaced, along with the almost-new 83 degree version, so I just put them in a pot of water and tried to monitor the temps when they opened etc. It was a pseudo scientific test insofar as it is hard to keep the water a uniform temp from top to bottom, but I did my best stirring and turning off the flame and not touching the probe to the pot, etc. Testing deficiencies aside, it sure seemed to show that these things START to open at the rated number. The 83C version (~181F) was only open about 1mm, if that, with a water temp around 83C, whereas the 71 degree version was fully open. Stove-top testing pretty much validates what I'm seeing in the car -- i.e., that the thermostat opens all the way, and the system finds its lowest cooling point (at least in hot weather), about 10C degrees above the rated temp of the thermostat. So, if you run an 83 degree thermostat, there's no mystery why the car wants to run closer to 93. Now, in much cooler weather, you could imagine the motor finding a lower running temp, since the cold air might allow the motor to stay cooler with the t-stat only partially open. But if you are in hotter weather and would prefer not to run in that 90-100C range all the time, I think it makes sense (in logic and practice) to jump down to the lower temp thermostat and fan switch.
Wanting to make sure I'm not crazy, I googled and found a Stat description that confirms exactly my findings. It says the rated temp is when the thermostat starts to open, and that it's not fully open until 15-20F (~8-11C) higher than the rated temp. How did I never know this?
Still not fully onboard with this because it totally goes against everything i was taught about cooling systems. So to recap, with a 71 degree thermostat fitted your temperature gauge was reads about 80 degrees, and you have tested that a 71 degree thermostat is fully open at about 80 degrees, and you are correlating the thermostat fully open temp with the engine temp as that is the same correlation you were getting with the 83 degree thermostat (~90 degree fully open) and gauge reading.
To me that is pure coincidence as the thermostat doesn't dictate engine temperature directly, its the efficiency of the radiator combined with the fan switch and fans that do that. So at 71 degrees your thermostat begins to open, passes coolant to the radiator and the radiator begins to cool that ~70 degree coolant while feeding the ambient (way below 70 degree) coolant already in the radiator to the engine. Due to continued spirited use and, lets call it hysteresis (though I know that not the right term but I'm no thermodynamic engineer), the engine temperature will continue to rise somewhat, lets say it gets to ~80 degrees as that is what your gauge is reading. Thermostat is fully open now and the radiator is doing its thing. Most modern radiators will have a 10 degree temperature differential between top and bottom hoses, so your engine will be receiving a constant supply of coolant at about ~70 degrees and that is what your gauge should be reading if you continue your boosted spirited run. If its reading a steady ~80 degrees that would indicate to me that your radiator is not very efficient, maybe a few rows are blocked and not cooling correctly.
So, I would expect an engine with a 71 degree thermostat to keep the engine at ~70 degrees, no correlation there, just coincidence, because that is just how it works out if the radiator drops the temp by ~10 degrees and the thermostat takes ~10 degrees to fully open. Same goes for an 83 degree thermostat, the engine temperature as measured at the gauge should be ~80 degrees. My comment earlier about keeping the engine at the optimal temperature, which I am relating to the stock 83 degree thermostat the engineers deemed necessary, was that anything below may cause increased fuel consumption, oil foaming, oil detergents not performing well, contaminants not being burnt off, etc. Its all been said before so I wont dwell there.
Apologies for the long post, these anomalies intrigue me and I like to get the the bottom of things. My understanding may be completely wrong, many more knowledgeable folk on here please correct me if it is.
Factory manual corresponds to that opening spec too:
Oh sure, read the manual and make it easy. Pfff….
Seriously, that's exactly what I saw, and clearly the missing link in the oft-recited logic about lower-temp thermostats. 90C is the middle of the gauge, so if the t-stat isn't fully open until 90C, it's no surprise to see the gauge hover above the half-way point in hot weather.
Still not fully onboard with this because it totally goes against everything i was taught about cooling systems. So to recap, with a 71 degree thermostat fitted your temperature gauge was reads about 80 degrees, and you have tested that a 71 degree thermostat is fully open at about 80 degrees, and you are correlating the thermostat fully open temp with the engine temp as that is the same correlation you were getting with the 83 degree thermostat (~90 degree fully open) and gauge reading.
To me that is pure coincidence as the thermostat doesn't dictate engine temperature directly, its the efficiency of the radiator combined with the fan switch and fans that do that. So at 71 degrees your thermostat begins to open, passes coolant to the radiator and the radiator begins to cool that ~70 degree coolant while feeding the ambient (way below 70 degree) coolant already in the radiator to the engine. Due to continued spirited use and, lets call it hysteresis (though I know that not the right term but I'm no thermodynamic engineer), the engine temperature will continue to rise somewhat, lets say it gets to ~80 degrees as that is what your gauge is reading. Thermostat is fully open now and the radiator is doing its thing. Most modern radiators will have a 10 degree temperature differential between top and bottom hoses, so your engine will be receiving a constant supply of coolant at about ~70 degrees and that is what your gauge should be reading if you continue your boosted spirited run. If its reading a steady ~80 degrees that would indicate to me that your radiator is not very efficient, maybe a few rows are blocked and not cooling correctly.
So, I would expect an engine with a 71 degree thermostat to keep the engine at ~70 degrees, no correlation there, just coincidence, because that is just how it works out if the radiator drops the temp by ~10 degrees and the thermostat takes ~10 degrees to fully open. Same goes for an 83 degree thermostat, the engine temperature as measured at the gauge should be ~80 degrees. My comment earlier about keeping the engine at the optimal temperature, which I am relating to the stock 83 degree thermostat the engineers deemed necessary, was that anything below may cause increased fuel consumption, oil foaming, oil detergents not performing well, contaminants not being burnt off, etc. Its all been said before so I wont dwell there.
Apologies for the long post, these anomalies intrigue me and I like to get the the bottom of things. My understanding may be completely wrong, many more knowledgeable folk on here please correct me if it is.
Sorry, missed all this before posting above. Give me time to digest what you said. In the meantime, all I can tell you with 100% confidence is that my car runs a good 10C+ cooler with the 71C thermostat. I went out and pounded on the car today, with AC and 20psi, and it never even got to half way between the lines. With the 83C t-stat, the car got to half way just driving around the block.
Sorry, missed all this before posting above. Give me time to digest what you said. In the meantime, all I can tell you with 100% confidence is that my car runs a good 10C+ cooler with the 71C thermostat. I went out and pounded on the car today, with AC and 20psi, and it never even got to half way between the lines. With the 83C t-stat, the car got to half way just driving around the block.
Understood and that’s great.
Another thing which surprised me was that you were running an 85 degree fan switch with an 83 degree thermostat, geez your fans must have been working overtime lol, I’d have thought maybe a 92 switch with an 83 thermostat, I know I have the official figures somewhere.
I don’t think my fans ever come on during a sprinted drive, though as soon as I begin to slow down or stop they will cycle on as the ram cooling goes away. Obviously the engine temperature continues to increase beyond the thermostat setting + 10 degrees and into the 90’s for the fan to kick in, but we are specifically discussing here the time driving hard without traffic just to be clear.
In my opinion, a lower temp main thermostat gives you more "head room" for higher coolant temperatures during spirited driving without traffic around or on a closed course. I run the lower temp thermostat and thermoswitch and have deleted the t-stat for the turbo loop. It warms up quickly and has never overheated or run hot. YMMV.
@Tom M'Guinn , I see now where my understanding of the system is wrong so please disregard. It really does seem that a lower temp thermostat would aid in lowering engine temperature in our engines without I’ll effects. Learn something new everyday 👍
06-05-2020, 09:17 AM
It says the rated temp is when the thermostat starts to open, and that it's not fully open until 15-20F (~8-11C) higher than the rated temp. How did I never know this? 
