Macster - you are right about capturing data to help sort-out the oil temp and coolant temp. They are related though; and seemingly more correlated under certain conditions. Unfortunately, the higher spot temp at the problematic cylinder area (see "bubbling" below) is washed out and is not seen at any gage. When I was switching over from standard tstat to lower temp tstat I did a study as you suggest and posted some of my graphs on the interwebz. Ambient temps make a difference. Rain makes a difference. (Sustained higher (> 3K)) Engine RPM makes a difference. Honestly, I was hoping for more reduced peak oil temps in hot conditions and high RPMs - but I feel a little more comforted that my cool down from peak temps is probably faster and that my peaks might be slightly lower - hopefully just enough lower to prevent the start of scoring. $60 tstat for $20k engine, kind of comfort. Further, season matters not, I have never had my oil level increase (due to likely water condensation or gasoline flooding) or other symptoms of that sort of contamination. Granted, DFW never really gets cold (one of the key ingredients in condensation of any liquid).

The 9A1 was a miss on my part - sorry. [I have the M97.]

As for tstat only for "warm up" (for M96/7) - I think not just during warm-up (and not really related to overall cooling capacity) because Baz offers this in his tome - "...thermostat that is basically set hotter than we think it needs to be to compensate for the other deterioration of various original settings and allowing critical temperatures to be reached too easily and localized bubbling/boiling to insulate the piston temperature from the cooling effect of the coolant nearby...if a lower temperature thermostat had also been fitted to reduce the individual HIGHER TEMPERATURE CYLINDERS BACK DOWN TO WHAT HAD ALREADY BEEN PROVEN TO BE A SATISFACTORY RUNNING TEMPERATURE IN THE OLDER CARS (ed. - emphasis is his).". [From Baz's Hartech's buyer's guide PDF 2012]

 

I've read Bazs article and most of Rabys posts and won't disagree with these experts regarding the open deck design of the m96/97 engine and their theories specifically regarding the problems with cyclinder 6 scoring and overheating and how a low temp thermostat may help. But, I don't think that's necessarily relevant to the OPs question of overall cooling capacity/oil temp readings of the closed deck design of the 9a1 engine. This is a common problem on the 997 forum of assuming what's good for the m96/97 correlates to the 9a1. The water pump replacement recommendations and fear of impeller blades erroding through the block or travelling through the engine is another example of this. The 9a1 has a different water pump design. Just trying to prevent false information that gets spread as gospel. And I hope I'm saying this gently. Not trying to ruffle any feathers.

 

You're right about the non-applicability to 9A1. Sorry I fed the false information for that motor/context.

 

I view cooling in a different way. A good cooling system is overbuilt to allow the motor to operate at its ideal temperature under all conditions. The thermostat should be such that it regulates to this ideal temperature at all times under all conditions.

Our cooling systems are a long ways from ideal.

As for the thermostat ... I won't battle the 997.1 motor experts. But bore scoring in the 9A1 motor has not been endemic. I believe most of these motors are running with the stock 175F thermostats. I don't believe we need to adjust our warm up cycle. And I want my oil to get hot enough to out gas any water. Since I only reach 175 oil temperature on wet winter nights, I certainly don't want a cooler rating. Note: Winter oil changes come at 4K instead of 5K on account of the lower temperatures. I also attempt to schedule frequent wet road enjoyment to get the temps up 8)


Other cooling systems ...

Pam's GLA 45 AMG has a display option to show water, oil, and transmission temperatures. These values appear to be quite accurate. Between hot dry outside conditions and cold wet, these gauges stay within a few degrees. The same is true for in city, freeway cruising, and at near red line operation in the twisties. The temperatures vary a bit but not much ... 5F or so.

At the AMG Driving Academy cars with over 20K miles of Accademy only use (abuse) were started in the morning and never shut off. They were at a standing idle or at redline on the track, driven by non - owners who could care less about the cars. The temperatures stayed within a few degrees.

In other words AMG designed an ideal cooling system.


My theory ...

AMG over designed their cooling system at the cost of weight. They could then design tight motors operating in tight ranges. Pam's 1.9 liter is pumping out 380 HP with 350 lb ft from 2500 rpm to almost redline. They do ultimately save weight via smaller motors. But these motors have to operate under tightly controlled parameters!!! And who besides MB wants to warranty a motor with 27 psi of boost and outputs of 200 HP per liter?

Porsche allowed for wider operating temperatures to save cooling system weight. I believe they were clever enough to design their motors to operate reliably across this temperature range.

Who (which company) is right? Both. So we can expect to see temperature variations in our cars. On the plus side, we know when we are out gassing the water in the oil!!!


And the question of how high is too high continues.

 

The Porsche cooling system is not under-built or built to save weight. Flat 6 engines do run hotter and thus, from a thermodynamics perspective, they are more efficient. The MB/AMG systems less so.

The reason the Porsche coolant gauge is pegged (mostly) at 175F is, I'm told, to quiet the anxieties of afflicted owners who seem to be constantly worried about engine temp variations. Air-cooled engines routinely run in the 250Fs and above and few complain; same should appy to wet engines.

 

Anyone run water wetter in their 996 or 997 cars?

 

No offense intended. My opinion only. We can agree to disagree. I've got several years of thermodynamics under my belt, so I have no problem with the concept of higher temperatures (as long as the intake is cold to insure air density). My discussion was on cooling, not efficiencies.

I am still inclined to believe that a consistent operating temperature for a motor is preferred. If that temperature is 250F as you hint at, then the cooling design should allow that temperature to be reached in cool rainy driving conditions rather than pegging at 175F. The same goes for any ideal temperature you define. Perhaps Porsche should have added a 250F thermostat to the oil cooler?

You mention that Porsche is lieing to us on the water gauge to quench anxiety. The oil gauge creates that for us instead!!! And the anxiety you mention concludes that temperatures should be consistent, per the average consumer.

Yes, the water temperature gauge lies to us. I disregard it. The oil gauge is what matters. Again the question is how high is too high? I haven't found that point yet, and am not sure how to define this. You used to know by the pinging of detonation. These days the computer hides that signalling.

To the OP, FWIW, 225F doesn't concern me. Nor does 250F. 275F might cause me to shut off the air conditioner and, as a last resort, diminish the fun factor 8)

Tony ... there is something you mentioned that I don't understand and would really appreciate clarification on. Why should a flat six run hotter than, say, a V6? The energy conversions are the same. If anything, the flat block should shed more heat since it is not folded back onto itself. You have a lot more experience than I do. Thanks in advance for your answer.

And OP, sorry for the left turn in your post.

 

I am not saying that 250F is the ideal op temp, but 225F might be. All cars I've driven are sensitive to ambient temp and typically run cooler on cooler days - the new MBs more so than most. On cold days... we just need to drive them harder...

Porsche block engine temps always fluctuate. The air-cooled usually have 2 stages - one when the block T-stat opens, and the other when the front oil cooler T-stat opens. They go up and down quickly. I would say, in my experience, on long drives, they average 200-210F. Short drives, especially with these modded low temp T-stats they never warm up, and that is not desirable, as most of us know. The new cars (991) have multiple T-stats - the water pump is thermostatically controlled - and that is done for emissions reasons.

I do not know if flat 6s have to run necessarily hotter than other designs. It is my experience, of owning several, that they do - both air-and-water-cooled. The engine being in the rear I speculate that they act more as a heatsink too. In any case these engines run well hot (at least the NA versions).

 

How hot is too hot? According to Lake Speed of Driven lubricants, their DT40 is OK up to temps of 300 degrees F - not that you'd want to be there for extended periods of time or all the time. Jake Raby says he sees 275-280 F on the track regularly. I'd say in street driving, if you're seeing temps like these then you have a problem with your cooling system - debris in the radiators, a thermostat not opening fully, restricting flow, etc. but 225-250 is completely fine. As Wayne says, at 275 you might take some avoidance measures like slowing down or switching off accessories like A/C that make the engine work harder.

As for the post on using Water Wetter, I'd avoid it. There are reports of it damaging cooling systems, congealing and clogging passages, etc - you can likely google and find them. If tracking the car where you can't use anti-freeze, just run distilled water per the regulations, otherwise run a 50/50 mix of Porsche pink coolant and distilled water.

 

In the old days, the oil cooler (heat exchanger) was exposed to air and the rate of heat transfer was proportional to the difference between the temps of the oil and air. But no more as the oil heat exchanger is placed within the coolant. When the engine is up to temp, the oil is hotter than the coolant otherwise there would be no heat transfer. What's a good delta? I don't know, maybe 30-60F?

To the OP: Get a cheap OBD reader and you'll be able to monitor your true coolant temp. But recognize that the OBD specs do not call for the oil temp so it is not available.

 

see that oil can on the bottom of the gauge. That’s a clue. That’s oil temp. 225 is perfect.

 

That oil temp is just fine, even up to 250.is ok. Driven oils are even good to 300.

Your coolant temp is the other gauge - the one that always reads 175 because it's not really a gauge, and reads that for any temp from 160 to about 225. If it ever moves up past the right side of the white line at 12 o'clock, pull over as you have a cooling system issue.