Low temp thermostats
 

I decided to start a separate thread to continue the discussion that grew out of Kashmir's low temp install thread(sorry for the hijack).

I have been working on cars, airplanes and motorcycles for many years, but my knowledge of Pcars is pretty basic. I say this because the reasoning for this three is not to argue, but to help me (and others) learn.

A special thanks to JFP for saving me from my over confidence in both my diagnostic and repair capabilities regarding what I thought was a leaking cam cover but turned out to be a oil pressure switch that was puking oil through the blade connector on the switch.

Anyway. The poll is what it is, I am more interested the reasoning behind the answers.

I am confused because I have seen the following stated (I've paraphrased for the sake of brevity) on this forum about low temp thermostats (LTT).

"LTTs make your car run cooler"
"LTTs can give you more power"
"LTTs make you your car heat up faster"
"LTTs cause your HVAC system to produce heat faster in the winter because the thermostat opens sooner"
"The stock thermostat is not all the way open at normal operating temps"
"These cars have hot spots exceeding 210df under normal operating condition that will not open the stock 186df thermostat"

I could go on but I'll stop for now.

I've already explained in the other thread my thoughts on why LTTs are snake oil, but I could be wrong...

So I'll start off with this question:

1) If the LTT allows hot coolant into the heater core sooner, that must mean that the heater circuit on Boxsters is not independent of the thermostat (radiator circuit) as it is with most other modern vehicles... is this the case? And if so... Given that the stock thermostat does not open adequately in summer, how is it that I ever get heat on a 35 degree fall morning?

Once I understand this, I'll move on to my other questions...

It has dropped my operational temp down to 180...

I am seeing a 40 degree drop in overall operational temp...which mean I am now running at 180 verses 220. A good modification and worth the effort.

I won't build an engine without one. I know what just 10 degrees of coolant temperature reduction can do for the engine. The factory knew too and the 987 and 997 illustrate it well.

I learned these things many years ago, but still today people want to argue with it, people always want to argue and the funny thing is most of them couldn't remove and replace their own thermostat if their life depended on it. If opinions were effective those people could move mountains.

I put a low temp thermostat in my car, but can't ell you if it is making much of a real differance since the temperatures where I live are currently 110+ degrees. What I can say is when I first got my car (last December) the temperature needle stayed right on the back of the 8 until I started to have water prump problems. Now, in the morning when it is less than 80 degrees it stays on the front of the 8. More or less. If I opush the car the temp will go up. I assume I'm hitting the capacity of my cooling system which is why I plan to add a third radiator to it. At worst, in the current temperature range, my guage hits the middle of the 0. Has neve gone past this point.

I bought my LT thermostat from a forum member, and didn't have a way to verify it was a low temperature thermostat either. Seems like it is since my car maintains a lower temperature for longer in the AM, but ...

So for a given temperature the LTT has a greater net area than a standard thermostat?

Jake, what does your last statement mean? Thanks.

I think what you are saying is that a factory 987/997 themostate is a 172 stat......not a 185 stat like the 986/996 have. Is this correct?

Drive a 987/997 and you'll find that the coolant temp sits rock solid at 175F.

I find the poll options a bit stilted; an option for "Yes, it makes a difference in the steady state operating temperature" is conspicuous by its absence..............

Agreed. My initial biases got that better of me. It was not a conscious mistake i assure you. My apologies! :o


Still no one has answered my initial question about the heater circuit and if it is independent of the thermostat.

OK, then I'll answer it: First, the heater core is always "on", meaning it has circulation even when the AC is running, but that circulation pathway changes during warm up. The M96 has a bypass coolant circuit that allows some low level volume of coolant to circulate while the thermostat is fully closed. This circuit is actually there to help prevent head cracking as they get hot very quickly. As soon as the stat begins to open, much warmer coolant begins to flow at a much higher volume rate, giving the driver much more heat.

well, since no one else will give a straight answer, yes the coolant going to the heater core does bypass the thermostat on p-cars, like any other car does, and a low temp thermostat can only reduce the performance of the heater.

may I go ahead and ask the next question?

Has anyone else monitored the coolant temperature on a 987/987 with an actual scan tool, and noticed that it does vary just like the older cars, but the gauge does not move?

I have seen this trend in temp gauges for the last 20 years or so. Porsche and Mercedes were some of the last to have actual temp gauges. Now pretty much every car that has a gauge is lying to you. It is no more effective than an idiot light at telling you what the engine temp is. In fact if it replaces all lights that would indicate a problem with temperature before damage can occur, it is less effective, since it is a lot harder to notice the needle jump from the center position to the top of the range once it gets out of the range that the controller is set to allow while it holds the needle steady in the middle.

P.S.: all M96/M97 cars use the same thermostat which includes 987s and 997s up to 2008, and I'm pretty sure the 9A1 tstat is the same temp but a different housing, or lack there of.

I will say, however that a lower temp thermostat can prevent an engine from running too hot, because by lowering the normal operating temperature of the engine, it will take longer for the temp to rise to dangerous levels when the cooling system's capacity to cool is overcome by higher ambient temperatures or hard use. It will still eventually get too hot under those circumstances.

Yes, I do it most everyday with an Autologic as I do my 86 mile test runs in customer's cars. Just did it this morning in an 08 Cayman S with my 4 liter package. I have also quantified the values using analog instruments and my 28 channel data logger with all stand alone sensors as well as OBDII channels. What I note is the coolant temps of the post 2006 engines runs substantially cooler than the older cars and though it may vary all the values are lower when compared to similar engines one generation older.

This is how we developed the lo temp T stat for LN in 2007. In temperatures as low as -27F heater performance wasn't an issue with the LN T stat. For a 1,000 mile trip the warmest conditions that were experienced were in the mid teens F. If the heat was reduced it wasn't enough to cause any issues or discomfort.

As I continue to develop Cayenne engines at elevated displacements and solving cylinder wear issues with them we are finding the same things as we noted with the M96. The dynamics of the thermostat housing changed dramatically with the 9a1 DFI flat six and now at 4.2 liters we ave learned just how far we can push them before mods need to be made and now I am developing those mods.

This is a pic of a factory bore from a 2012 Cayman R with 4,400 miles on it that I disassembled as a base for my 4.2 build. All the cylinders were this worn at 4,400 miles with zero track time. Welcome to the next generation.
https://fbcdn-sphotos-f-a.akamaihd.n...44931594_n.jpg

Here is another cylinder on the opposite side of the engine.
https://fbcdn-sphotos-h-a.akamaihd.n...27401515_n.jpg

Back on M96s, we tore this 27K mile factory Porsche crate engine yesterday as it sounded like it had bad lifters, but it didn't. The noise was a toasted cylinder and piston that was rocking at mid-bore and creating the ticking sound.
Here is the piston
https://fbcdn-sphotos-e-a.akamaihd.n...06091049_n.jpg

And its cylinder
https://fbcdn-sphotos-g-a.akamaihd.n...52898315_n.jpg

So the 05 987,s run hotter than the 06 987,s.Am i reading this rite Jake?