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Old 09-02-2012, 07:24 AM   #1
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Engine Thermostat, Low Temperature (begins opening at 160 deg F)

I'm curious as to why install a lower thermostat when the manufacturer installed a 186 deg F from the factory.
I'm trying to find the benefit gained by lowering the threshold of coolant passing through the motor sooner.
I searched this forum on the topic and did not get the logic of doing it.
The engine runs around 190 deg F with the factory OEM thermostat rated at 186.8 deg F. (Car gauge indication 190 deg F Not being exact here, and yes i understand that reading is after the return from the radiator.)

It would appear to me that a lower thermostat would only cause to motor to take longer to reach operating temperature since it's passing coolant sooner to the motor.
I seen comments as to "I replaced my thermostat to the 160 deg F and my car still runs at the same temperature". Thus not getting the concept of the lower temperature is only opening fully at the lower temperature.
The car is still going to obtain it's normal operating temperature eventually.

I guess my question is the logic as to why change the manufacturers thermostat specifications to a lower temperature?
I'm trying to understand what benefit is gained.
To me, my car seems to run at it's best when the engine reaches it's full operating temperature.

While I seen other aftermarket parts change specifications due to enhancing the performance or better quality component replacement.
Example with the LNE IMS bearing being an improvement over the factory IMS bearing.

I'm not trying to stir up a can of worms, just trying to understand the benefit.
Thanks
T

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Old 09-02-2012, 08:23 AM   #2
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this is hearsay, but i've read that porsche keeps the temps up on their street cars for emmissions purposes (cats work better); on their cup cars they run 160 degree tstats.
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Old 09-02-2012, 08:23 AM   #3
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OK, first let’s clear up a couple of misconceptions: First, a lower temperature thermostat regulates the lowest temperature the engine will run at, not the highest. That said, cars running the 160F stat tend to run substantially cooler in a “steady state” condition (open road, constant speed recorded temps in the mid 170’s are common). Stuck in traffic, a car with the 160F stat will heat up just like one with the OEM stat, but it will take longer (starting from a lower temp), and will eventually cool back down to the lower steady state temp once the car is moving at speed again. Second, the OEM stat opens at 186F, but the car runs much hotter than that; usually in the 210+ range (the dash gauge is woefully inaccurate). It is not unusual for a car with an OEM stat to have coolant temperatures well north of 200F at the same “steady state” conditions. Third, these cooling system’s have documented “hot spots” in them where the coolant sees even higher temperature’s due to flow restrictions in the system, etc.; running the lower temp stat (and the inherent lower coolant temp) help reduce the temperatures at these hot spots somewhat. Fourth, the cars do not take any longer to warm up, temp rise from startup is a function of the initial ambient air temp and the volume of coolant, neither of which is altered by changing the thermostat. In fact, many owners comment that the car appears to warm up more quickly with the low temp stat, which is an illusion created by the coolant beginning to circulate sooner (the gauge moves sooner, heat comes out sooner, etc.). In actuality, once the stat opens, the 160F stat slows the process down as it begins to transfer heat out at the radiators, but that creates no issues, contrary to most “urban legends”. A lot of people seem to believe that running the lower temp stat is going to foul the oil with water and unburned fuel; but that simply does not happen as repeated used oil analysis have proven; the oil still gets plenty hot enough to flash off any volatile’s, as it is under a constant vacuum condition any time the engine is running. Perhaps more interesting, UOA’s have shown that just going to the 160F stat lengthens the oils life, most likely due to the fact it is typically running 20-30 degrees cooler most of the time.

Outside of lowering the engine and oil temperatures, the other major advantage to running the car at lower temperatures is a slight but measurable improvement in volumetric efficiency of the engine and reduced pre-detonation characteristics. On a normally aspirated engine, this would show up as slight but measurable increases on a dyno, but is more commonly noted in real world driving as a slight improvement in fuel mileage.

Another point worth pondering is the fact that Porsche uses the same low temperature stats in some of their production cars: GT2, GT3, and the Turbo…….
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Old 09-02-2012, 08:24 AM   #4
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Originally Posted by The Radium King View Post
this is hearsay, but i've read that porsche keeps the temps up on their street cars for emmissions purposes (cats work better); on their cup cars they run 160 degree tstats.
That is correct.
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Old 09-02-2012, 09:00 AM   #5
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JFP in PA:
Thanks for your feedback..
Much appreciated.
T
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Old 09-03-2012, 07:05 AM   #6
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The higher temp thermostat on a street car is also related to oil change duration.

Running a low temp thermostat may not allow the engine to heat up (depending on the weather and your driving) enough to burn off the moisture in the oil on a regular basis. Running the 186 deg thermostat tries to make sure that the engine gets to full temp more readily and thus allows Porsche (and almost all other car makers) to extend oil changes to more than 10,000 miles.
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Old 09-03-2012, 08:43 AM   #7
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The higher temp thermostat on a street car is also related to oil change duration.

Running a low temp thermostat may not allow the engine to heat up (depending on the weather and your driving) enough to burn off the moisture in the oil on a regular basis. Running the 186 deg thermostat tries to make sure that the engine gets to full temp more readily and thus allows Porsche (and almost all other car makers) to extend oil changes to more than 10,000 miles.
In actual fact, it works the other way around: As noted above, the combination of engine vacuum in the sump and 170-180F coolant temps has demonstrated (by multiple used oil analyses) that there is no fuel or water contamination increase when running the lower temp stat; and the lower oil temps afforded by the lower coolant temps lengthened the oils ability to stay in grade, not shortened it.
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Old 03-14-2017, 08:37 AM   #8
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....wrong thread...
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Old 03-15-2017, 03:09 AM   #9
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So, why are we not replacing the radiator fan limit switches to have the fans kick in at lower coolant temperatures?
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Old 03-15-2017, 04:44 AM   #10
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So, why are we not replacing the radiator fan limit switches to have the fans kick in at lower coolant temperatures?
On my AX car I've wired in a pair of manual switches for the fans. The temp gauge never hits the 180 mark now (I don't let it). High temps are the enemy of the m96 engine!
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Old 03-15-2017, 05:43 AM   #11
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I thought the fan resistors default to high speed if there is a fault?
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Old 03-15-2017, 06:03 AM   #12
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So, why are we not replacing the radiator fan limit switches to have the fans kick in at lower coolant temperatures?
The radiator fans are controlled by software in the DME, not switches. Changing when they go on and off requires reprogramming the DME, which is anything but easy.
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Old 03-15-2017, 06:04 AM   #13
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I thought the fan resistors default to high speed if there is a fault?
Usually, the just stop working.
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Old 03-15-2017, 06:15 AM   #14
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What about the effect on engine clearance tolerances that Porsche designed into
the engine based on 186 and above temps? I race motocross dirt bikes which have no thermostat so and I always start the bike and let it idle until full normal temp before ridding. This expands the piston and keeps the piston rings tight against the cylinder. Even in Arizona the winter is pretty cold we have to cover one of the radiators to keep proper temp, now we do change oil very often but they do rev to 11000 - 130000 rpm. Our Boxsters have lots of miles on them so clearances are getting pretty sloppy so I always get it up to full temp before driving hard.
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Old 03-15-2017, 07:16 AM   #15
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What about the effect on engine clearance tolerances that Porsche designed into
the engine based on 186 and above temps? I race motocross dirt bikes which have no thermostat so and I always start the bike and let it idle until full normal temp before ridding. This expands the piston and keeps the piston rings tight against the cylinder. Even in Arizona the winter is pretty cold we have to cover one of the radiators to keep proper temp, now we do change oil very often but they do rev to 11000 - 130000 rpm. Our Boxsters have lots of miles on them so clearances are getting pretty sloppy so I always get it up to full temp before driving hard.
While there is no hard engineer data available that I am aware of, several shops (mine included) have literally hundred's of customers running the 160F stat, some for many years in daily drivers, none of which have shown any adverse effects on engine hard parts. As a normal course of maintenance on this group of vehicles, we have done a variety of diagnostics (leak down, compression tests, bore scope, etc.) and have not seen any real difference other than significant improvements in the UOA analysis.
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Old 03-15-2017, 08:16 AM   #16
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JFP, have you found any benefit to a low temp thermostat in the 9A1 engines?
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Old 03-15-2017, 09:40 AM   #17
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JFP, have you found any benefit to a low temp thermostat in the 9A1 engines?
The 9A1 engines do not use a simple thermostat like the M96/97, they have a more sophisticated "thermal management system" which is electronically controlled. Would they benefit from running a bit cooler, sure, but how to do it becomes the issue.

From Porsche literature on the subject:

"The required changes to the engine consist of a single-slider map-controlled thermostat and a shut-off valve in the bypass circuit. The separation of the functions of coolant temperature regulation and bypass circuit shut-off offers advantages in temperature regulation and permits a heating boost in the warm-up phase with a weight-optimized design. The system in the basic engine consists of only 3 additional components(shut-off valve and bypass line with tube). With thermal management, the coolant throughput through the engine is completely suppressed by closing the shut-off valves in the early phase of the warm-up. This leads to faster warm-up of the cylinder head and liner. In the second phase, the shut-off valve is opened and the engine oil and transmission oil are warmed directly, reducing friction. "
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Old 03-15-2017, 10:06 AM   #18
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JFP if the low temp thermostat is so good, why would Porsche have specified a higher temp one? Was it based on predicted use patterns for the "not a race car" Boxster as opposed to the GT cars where racing was predicted? How does the low temp affect emissions? Is there any dumping of more unburned gas (think choke here) into the cats as the "choke" system stays on longer?
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Old 03-15-2017, 10:34 AM   #19
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JFP if the low temp thermostat is so good, why would Porsche have specified a higher temp one? Was it based on predicted use patterns for the "not a race car" Boxster as opposed to the GT cars where racing was predicted? How does the low temp affect emissions? Is there any dumping of more unburned gas (think choke here) into the cats as the "choke" system stays on longer?
It was done strictly for emissions purposes.

We have put emissions exhaust "sniffers" into cars before and after the 160 stat install, and actually found slightly lower emissions at idle with the 160 F stat, which ties in with the better gas mileage claims by owners. We did not run the car for prolonged periods at varying RPM's, so I have no data beyond our simple test.

We have customers that have run one of these stats in daily drivers for over 100K miles, and their cats are still fine. Interestingly, we see more correlation between cat failures (read non mechanical cat damage) and running cheap gas, those that always buy the cheapest they can find seem to have more problems than those that stay with major brands of fuel; and this correlation also seems to apply to non Porsche brand cars as well, so I would tend to point at fuel quality as the major determinant for cat failures we see.
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Old 03-15-2017, 12:41 PM   #20
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Why Why Why???

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Originally Posted by mikefocke View Post
JFP if the low temp thermostat is so good, why would Porsche have specified a higher temp one? Was it based on predicted use patterns for the "not a race car" Boxster as opposed to the GT cars where racing was predicted? How does the low temp affect emissions? Is there any dumping of more unburned gas (think choke here) into the cats as the "choke" system stays on longer?
You guys are way more informed than me and I appreciate all the good stuff I learn here. I love my Boxster but can no longer wonder why Porsche makes some or the choices they do like -
  • use a sealed, greased, ball bearing on the IMS which is submerged in the sump. The use of a common casting for both cylinder heads required the IMS, but at what point did someone say, "Hey, how should we put a bearing on this end of the IMS?"
  • use a grade of plastic on internal headlight lenses that will turn dark with burn marks even if you only ever use stock halogen light bulbs.
  • use soft-touch black paint on interior trim panels that turns sticky with age.
  • design and specify a water pump that should be replaced at intervals to prevent engine damage from broken impeller bits migrating to cylinder heads and causing hotspots.

Signed, glad I don't own a GT2, GT 3 or Turbo requiring me to have my cooling system fitting welded to my engine block!

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