Bruce In Philly

I understand the DFI engines have lower-temp thermostats. Why are these engines designed to run at lower temps?

I got onto this subject researching the possible purchase of a 160 degree (lower than factory) thermostat for my 2009 C2S. Some believe lowering the thermostat spec will increase the life of the engine and that the only reason they are so high is to hit emission laws. Others say engines are most efficient and powerful at 180 or whatever and that lowering the temp robs efficiency.

I exchanged emails with an engineer at an aftermarket company who sells lower temp thermostats and asked why they don't have them for my car. He noted the DFI engines already run at the lower temps.

I don't want to flame the fires of this yes or no topic of thermostats, but the DFIs do run at lower temps. Any knowledge about this Porsche design change?

Peace
Bruce in Philly

Macster

Interesting question. I put this to some techs I know to see if they know why.

Just got an answer back: The newer cars have an electronically controlled T-stat which allows much more precise coolant temperature control.

Of course this raises lots more questions -- one is why the 160F classification? (which suggests a possible answer: Maybe this is the lowest adjustment range?) with the DME actually adjusting this to perhaps 190F or even higher -- but I do not have time to dig deeper right now.

Robocop305

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CAVU

When I look at the repair procedures for my 997.2, I don't see a requirement to remove an electrical connection and the only picture I found of the part 9A110622501 didn't appear to be electronically controlled (but it could be a wrong picture)

I think it's a great question but I think the answer still alludes us.

Macster

I agree a really great question.

The word has been that t-stat is going away and we could be on the cusp of this. I mean these engines already rely upon the DME for management of oil pressure (not to mention fuel, spark advance or retardation due to in some cases detonation) why not coolant temperature too? Pumping gallons of coolant around all the time is a big waste of power.

Anyhow, no response yet. When it gets quiet generally this is a sign the techs are busy.

In the meantime, the T-Stat proper may not be where the control is. It may be the same old same old the actual valve that controls coolant flow is located elsewhere.

There is the possibility the control is via in part by flaps that control the amount of air allowed to flow through the radiators.

Regardless of what i hear or do not hear back, I will probably be at a dealer sometime next week and I'll see if I can face to face get more info.

A DFI engine -- it could be in an Cayenne though instead of a 997.2 -- is possibly in my future though a year or so away but I want to learn more about these DFI engines in the meantime.

slicky rick

Maybe macster is referring to the additional techs in the 991 engines. Though basically the same engine as our 997.2's, there is the so called thermal management system which i think is the electronically controlled cooling system. Zero flow of coolant for the first few minutes for the fastest heating time, and then slow opening of a valve controlling water flow through the system or maybe an electronic control for the water pump itself. Something similar to the control for the oil pump. Might be a good idea but sounds too risky for me if something fails.. I think... We will soon see a water pressure gauge in instrument cluster... Im just speculating here guys just babbling.

ecostellodo

A data log from an OBD reader would tell us what we need to know about engine temps.

Macster

Agree. I have the data logger but not the car to put it in.

lurchphil

My 2012 997.2 has had a strange coolant temperature issue. I was driving on Hwy 101 near Santa Maria and noticed that instead of its normal 175 degree indication, it was showing about 130 -140 degrees. Later, it went back to 175 degrees. The oil temp was also lower than normal. My guess is either the coolant temperature sender is the problem or the thermostat is sticking open. Since I am under CPO, I will be having it checked at the dealer Monday. Anyone else have this issue?

Macster

Some few years ago in my Turbo heading west out of Flagstaff on I-40. Long sections of down grades and on one I think I decided to let the car coast in gear, 6th gear. At some point I happened to notice the coolant temperature gage needle had fallen from the "180" mark to not quite half way between that and the lowest reading. Kind of caught me off guard. No oil temperature gage so I do not know if the oil temperature dropped. I do not recall the oil pressure reading being different.

I was nearly at the bottom of a long downgrade and the temperature came back up to normal quickly enough and there was no other sign of any issue since.

Lower coolant temperature *and* oil temperature suggests the T-Stat stuck open. The problem is if (big if) this is the case likely the problem will be intermittent.

Not enough to warrant a preemptive T-stat (and I guess water pump) replacement.

Be interested in what the dealer has to say about the behavior.

Tcc1999

If the T-stat is electronically controlled through the ECU, then wouldn't it follow that if the temps fell outside of what PAG engineers considered "normal" operation, a code would be thrown? This assumes that there is an "if-then" statement in the ECU code in the first place. So if the answer is, "yes" there is a code for this, should we worry about an analog gauge showing a number that the ECU is not programmed to indicate as a malfunction or problem?

Just askin'.

Wolfk

Macster, I call BS on your techs, part 21 thermostat, looks like same old style used for decades, just saying.

andy92782

I think I'll follow this thread.

Two thoughts:

1) The coolant temperature gauge on the 997.2 is an idiot gauge. Unless something is clearly not normal, other than the warm-up period it shouldn't read anything other than straight up 175F. It's controlled by software, not directly by temperature.

2) Back in my misguided youth when I owned and hot-rodded a '96 Camaro Z28, one of the things I did to it was install a 160F thermostat (stock 'stat was 190F). I also had the ECU reprogrammed to turn the radiator fans on earlier. The theory is that the cooler an engine runs, the less heat soak it develops and the stronger and more consistent it performs especially when making mulitple runs at a drag strip. In practice I'm not sure it did much of anything. One thing I'll say about that car before I modded it: The coolant temp gauge actually worked. If you were steady-state cruising on the freeway it would read about 1/4 the way up - presumably the 190F temp of the thermostat. If you sat idling in the In-N-Out drive-through with no airflow it would heat soak and the gauge would creep up to over the 1/2 way mark before the radiator fans kicked in (at ~220F) and knocked it down to about the 1/3 point, at which point they turned off. The cycle would then repeat. I'm sure this happens on our 997s as well but the software just keeps the gauge pointed straight up. It reduces service calls

Macster

The word I got and this was some time ago and I never came back to update the thread, is the old style T-stat is still in service but it is a lower temperature to essentially get it open (and out of the way so to speak) so the other T-stats (or valves) controlled by the DME can better control temperature and allow the engine to heat up more uniformly.

I never got a chance to really get into this with the techs and I have *not* seen any real hardware to gain a better understanding of what's going on.

Also, I do not recall the MYs in which the the newer coolant temperature control system was implemented.

In those vehicles/engines without the newer system just the plain old T-stat ( I guess ) is used.

chuck911

It might not be quite the right question. The common assumption is all Porsche specs and factory recommendations are in line with what us owners want. There are lots of reasons and examples indicating this is not always true. Yet it continues to be the common assumption.

The other assumption is the new one is different so why did they design it different? Well, it could just as likely be that neither design is any different with regard to temp, at least in terms of power output and longevity. You know, stuff we care about. Both engines will probably run longer if run cooler. Kinda hard to argue otherwise, being how it flies in the face of everything ever, forever and ever. But to meet emissions, they may have needed higher temps in the older design, less so now with DFI. That probably is all that it is.

At least, it makes more sense than the BS that tech tried to feed Macster!