Whenever extra engine cooling is needed a third central radiator is mounted from factory even on a 991 ( MY12+).

Also, when comparing the 997.2 and 991 models you have to make sure that all the radiators' dimensions/engine cooling efficiency are the same... are they?!

 

I live in South Florida and the oil temperature never goes beyond 220 with my driving style. I have a 997.2 without a 3rd radiator.

 

Then, you have to ask yourself why did Porsche adopt a stock 3rd radiator for MY11 997.2 Carrera S PDK onwards, independently of where one lives?

It is my belief that Porsche did this from past learning experience while developing the soon to be released 991 by then, which has in fact a more sophisticated coolant thermal management and DFI systems with a map-controlled thermostat for the former and multi-hole (one central and 5 peripheral holes) injectors for better fuel atomization in the latter, as opposed to a single hole swirl effect injectors used on the 997.2 - two somewhat weak points of the 9A1's first generation engine.

Accordingly, former 997.2 owners that have made the move to the 991 are consistently reporting better and more easy revving engine performance, better gas mileage and oil consumption rates.

As for oil temps it is very interesting to note what a 991 owner says about the stock Sport button effect :

 

I know about the changes made, but I'm just pointing out my experience. It takes a while for my car to warm up. In order for mine to get to 225, I have to operate my car on Sport mode and drive aggressively. In my case, a third radiator would be another part to fail or more connections to leak.

 

Same here.

 

Guys, you are forgetting that the temp gauge is showing you what Porsche wants you to see... Its a calculated value.

To see real coolant temps, employ a stand alone gauge, or read directly from the CAN. I don't even trust the CAN, honestly.

 

Jake, how accurate is the oil temp gauge? That's what I go by. Thanks.

 

Its 100% accurate, to the calculated value that someone wants you to see.

Again, I trust no data unless its coming from the CAN, or better yet, a stand alone means of data acquisition.

I use OBDII very infrequently, as I tend to like raw, unaltered data during development.

 

The question is not so much the temp you see at the gauge BUT the temp headroom made available for the engine to run within the safety margins, namely when driven hard - Sport mode ON! That's what is important really, because no gauge at the instrument cluster, or a stand alone one for that matter, will ever tell you about hot spots formation over critical engine parts, unless all the engine is already too hot.

The 3rd radiator allows just that - to lower the engine running temp floor. At some point Porsche realized that this should be carried over to all stock Carrera S PDK models. For the manufacturer it's always a compromise between minimum production cost vs desired product efficiency and reliability. Objectively, a 3rd radiator will always represent both an additional production cost and reduced fuel efficiency, unless there's some kind of map-controlled coolant thermal management system to optimize the latter. Since the Carrera S PDK engine already runs hotter in average than it's manual counterpart due precisely to the PDK transmission and its cooling need, the 3rd radiator addition in this case doesn't prejudice fuel efficiency as much and engine reliability is much improved.


My target is a MY11 or later 997.2 Carrera S PDK!

 

Porsche has gone back and forth with 2-3 radiators since the beginning of the water-cooled 911. The earliest 996s only had two radiators, with a 3rd radiator option, then they added a 3rd radiator standard for a few years, then took it away again. This was also done with the Boxster S, and then again with the Cayman S (Gen1).

Coolant cooling means little to me. I have learned that the thing that keeps the engines alive is keeping a ton of oil volume, and keeping that oil cool. The factory heat exchanger with all water-cooled Porsches (except the Cayenne) is marginal at best and it is more designed to heat the oil up faster, keeping it more linear with the coolant temperature in the cold, more than anything else. I collect data all the time that proves these engines will run 20 degree higher OT on the highway, than CLT. On the track the factory heat exchanger does very little and OT will easily be 40* higher than CLT on a 90 degree day. This proves that the factory heat exchanger is thermally overloaded. People often go to t larger heat exchanger, and think they are doing something, when in fact all this does is heat the oil up faster.

With the current cars the addition of PDK drives the 3rd radiator necessity more than anything, since the coolant serves a secondary role, outside of engine cooling.

To me, a 3rd radiator does very little in the big picture. I'd rather hang my big, hand built, air/ oil cooler in the front of the car, in the same place where the factory oil cooler goes. Doing this, I omit the heat exchanger from the engine, and partition the oil cooling from the coolant cooling, omitting the factory mindset completely. When doing this OT runs cooler, and so does CLT, why? Because now the oil cooler is cooling the oil, and the radiators are cooling the coolant. Taking the oil cooling away from the CLT reduces load on the CLT system, adding the air/ oil cooler only works well in hot climates/ track service, otherwise the oil takes too long to heat up.

My oil system can include a thermostat, but it complicates plumbing. I only install these on my engines, and it can be used in conjunction with my dry sump engines.

Put simply, you can add all the radiators that you want, but you'll run out of space to hang them all, before you make an impact in the oil temperature issues. We don't see negative effects from high CLT with ANY water-cooled Porsche engine, all of them have issues related to viscosity loss, thats directly attributed to thermal breakdown. Running crappy oil, and not changing it frequently enough is the other major contributor.

Hot coolant won't send a connecting rod through your block, but hot oil will.

 

That is not a valid conclusion. The oil temperature is increased significantly on the track because the engine is producing more heat. In fact, if the oil temperature is 40F higher than than the coolant, a greater amount of heat transfer is taking place than if the delta is 20F. The higher oil temp means that it is transferring heat from the engine to the coolant at a significantly higher rate. By the way I observe that the oil temp drops in my car when cruising on the highway ( lower fuel consumption and higher air flow rates). The oil temp rises in my car when driving at 40-50 mph and revving the engine at 4-5K rpm rather than 2.5 -3.5K rpm in summer. Higher fuel consumption and lower airflow rates.

 

Of course, and most of that heat comes from the valve springs, as oil is the only thing that cools them. RPM= More friction, which will increase the oil's temperature as it works to soak the heat up. The issue remains, that the factory heat exchanger is thermally overloaded and can't remove the heat from the oil. I have seen OT of 290F in an early 996 engine, and over 280 in a 9a1, both measured with stand alone data acquisition, in the sump.

Oil temps this high, and 60-80F higher than the coolant temperatures simultaneously, proves that the oil is not being cooled effectively.

Absolutely. Good air flow, low engine loads and lower RPM will all equate to that. Again, if you are using the factory gauges only to make these determinations, you are not seeing the full picture.

Absolutely. OT is always more impacted by ROM that CLT. Thats because the friction from the RPM is still there, no matter the load, and the valve springs are working harder at higher RPM as well.

You can easily see higher OT readings at 4-5K RPM in winter, than you'll see at 2-3K RPM in summer.

 

Well Jake, that's how manufacturers boost fuel-efficiency and reduce emissions, by controlling engine coolant temperature and therefore combustion chambers temperature.

Someone has to care about fuel-efficiency and emissions... Flat6 Innovations task is easier!


CORRECTAMUNDO!!!


And that sums it all, doesn't it?!


And here is where the issue lays... oil temp is directly influenced by the coolant temperature simply because it's the coolant that keeps the oil temps in check via the dedicated oil/water heat exchanger as long as the oil runs hotter than the coolant - that's the heat exchanger working principle!

So, a 3rd radiator will definitely make a difference as long as it effectively contributes to lower the coolant temperature. Sometimes, it is even enough to simply enlarge the air openings for the side radiators. But then again, there's the aerodynamic efficiency factor that influences performance and ultimately fuel-efficiency and emissions.

As you say, adding a larger oil heat exchanger without adding extra coolant cooling capacity, by means of, say, a 3rd radiator, only serves to heat up oil faster.


Don't think failing connecting rods is the major problem with water cooled Porsche engines.

 

Just out of interest, what is the maximum temperature the oil can safely take? Surely 290F is no issue?

 

You can fry chicken at 300*F, just to put it into perspective.

Thats a blanket statement. Oils vary a ton, especially in their HTHS shear properties. This property is often overlooked in oil comparisons, as modern passenger cars have their oils tested, and rated at 100* C. Above that point most oil manufacturers don't give a damn what the oil does, because they aren't being evaluated there. Your 40 grade oil, thats a 40 grade at 100*c, damn sure won't be a 40 grade at 290F!

So, the oil's ability to maintain viscosity at higher OT is the key to HTHS and how long the oil will live at the elevated temperatures.

I have found that most oils that can be bought over the counter don't like more than 250F for very long. Full-on race oils can sometimes take 300*F for 750 miles of on the hammer driving. The difference is these oils are designed with a dispersant package that fits this bill. Its not something that you can buy at Walmart.

Its my goal to keep OT at 260F or below, but every engine is different, so I use TAN, TBN and Oil Pressure readings to help me evaluate an oil and where it's sweet spot truly is.

I want to stay out of that 275+ range at all costs, and we've done that, even in Grand Am applications. The key is an oil that will live at those temps, and then, further making adjustments to clearances and components so the heat isn't generated in such excess numbers.