Why lower coolant temps in 997.2 & DFIs?

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

The oil temperature will have tens of degrees of difference, depending on internal and environmental factors.

My DFI runs at 200 as well - but the oil has run as high as 232.

Quote
Bruce In Philly (2000 S Boxster, now '09 C2S)
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

the engine runs. That is controlled by how much heat the cooling system can remove from the engine and release to the air flowing through the radiators. Even though my Boxster comes with a 190F t-stat its max. coolant temperature is 36F hotter than that, 226F. Above 190F the t-stat is out the picture.

While I haven't heard back more from my tech contacts I've been digging into this through other channels and it appears what is going on is the lower temp t-stat is selected to mainly get it it out of the way, to have it fully opened at a lower temperature, so the electronically controlled temperature valve can be used to more precisely control engine coolant temperature. The engine still runs way hotter than the 160F t-stat would suggest, but the temperature is kept more stable, with less variation.

(My WAG is the next step would be for Porsche to do away with the traditional t-stat altogether, which I think some other automakers have already done.)

Anyhow, my Boxster's coolant temperature on a mild day can range from 190F-195F at legal highway speed to 226F pushing the engine hard in the twisties. Same day, same ambient temperature, both the twisties and the highway within a few miles of each other.

There is the flip side. I've never seen this with my Boxster but I saw it once with my 996. Coming down a long mountain grade -- I can't recall now where but I think it is the one west of Flagstaff on I-40 (the elevation drops from over 7700 feet to around 2500 feet from Flagstaff to Kingman but in between there are areas where the road dips so one gets the benefit of a rather large drop in elevation over a short distance -- miles vs. scores of miles. But there are a few other places on I-40 inside CA where while the starting elevation is not as high the road drops for several thousand feet over a distance of miles and the car can essentially coast this entire distance even (at least in the case of my cars) even in gear. The car can coast and yet maintain speed without the engine really working much. Anyhow, during one such descent I glanced down at the dash and noticed the coolant temp gage needle had dropped from its normal spot almost directly over the "180" hash mark to about half way between that mark and the cold position. This was a bit of a shock to me as the needle once the engine is up to temp just stays on that hash mark maybe moving a needle width above it but never below it. I scanned the rest of the dash looking for any other signs of trouble and thankfully spotted none then it occurred to me that the car had been coasting a lot. Even though I had the transmission in 6th gear and the clutch was engaged the down grade was steep enough that the car's speed had not been slowed by engine compression. (The Turbo only runs a 9.4:1 compression ratio compared to the Boxster's 11.3:1 CR.) The engine had essentially not been running -- under closed throttle no gasoline is injected -- for miles -- and as a result the engine had cooled way down. This much of a cool down is not good.

What I expect I would see with the new engine would be is the temperature probably above 190F but not as high a 226F. The engine cooling system has more cooling capacity but its performance is controlled/limited so it doesn't overcool a lightly working engine and yet when the engine is working harder can use its added performance to keep it from running as hot as an engine of the older design would run under similar conditions.

Things have not changed. These engines simply run better, suffer the least amount of wear, operating at above 200F. Ideally whatever the engine designers believe is the ideal temperature (call it 210F) the cooling system would be able to keep the temperature there. I think that is a bit impractical given the difference in heat an idling engine generates compared to one running at WOT at redline. So there will still be some range of temperature variation. But overall the engine's operating temperature will be more narrowly confined.

One of these days I'll ask a tech when he takes a DFI equipped car out on a prolonged test drive to plug in a monitoring device that captures coolant temperature and afterwards I can view a graph of the data along with intake air temp and engine load and see what the coolant temperature does.