wf758

ltc (Lewis) and others have commented that if they were to purchase a new Porsche, it would only be a GT2, GT3 due to their engine setups versus a standard 996/997. I think someone mentioned it had something to do with the sump? Given that I'm obviously non-technical, would anyone care to elaborate? Thanks!

jimq

The 996TT also has the same basic block as the 964-993 like the GT2 and GT3. Some dont like the turbo as much because of some lag. From what I have read the block is a 964.xxx part #.

Chris M.

Of the water-cooled cars only the Turbo, GT2, GT3, GT3RS, Cup, and RSR have dry-sump engines with the 964 block. All the other 911 variants as well as the Boxster and Cayman have wet sump engines.

wf758

sorry to be ignorant here (not the first time)...but does this mean they remain air cooled, or they water cool in a different way than the 996/997s?

dfinnegan

Both air cooled and water cooled engines have an oil circulation system. The oil pump sits at the bottom of the engine, in the sump. It then pumps the oil out to the oil cooler and back to the various parts of the engine. From the heads the oil drips back down to the sump to be recirculated.

A wet sump engine has a reservoir at the bottom of the engine. This is where the oil sits when the engine is not running.

On our air cooled cars we have a dry sump. The reservoir at the bottom of the engine is very small and only serves to house the pump. The oil reservoir is external to the engine. In our case, it's in front of the right rear wheel.

In a wet sump engine, depending upon the design, the oil can slosh around when cornering hard. This gives rise to starvation of the pump and the engine gets no oil for a brief period of time. Generally this causes engine failure. The dry sump is considered a better design for that reason. I expect that modern wet sump systems do not suffer from this problem.

The cooling of the engine is via air or water. Our air cooled engines have a large fan at the back of the engine and a shroud which directs the air down over the engine block for cooling. There is also a cooling component provided by the oil, thus the large quantity in our cars, but air is the primary cooling system.

In water cooled engines there is a jacket around the block which holds water. The water is circulated much like the oil, though in a seperate system, of course. It is directed out to the water cooler (radiator) and back around the engine. The jacket is more of a cavity system built into the block.

I can't speak to the pros and cons of air vs water cooling, but I expect someone here could.

SimonExtreme

A few things on this. First, IMO, there is a bit of a myth about our air cooled engines. I would suggest that it would be better to call them oil cooled with air assistance!

Anyway, back to the thread! The real issue is that on the standard 996 and 997's have a different engine from teh GT3 and turbo. The standard engine has some very significant reliability issues (how to start an arguement!) which the other engines don't have. Because fo this, I wouldn't own a standard 996 or 997 without the benefit of a very good warranty!

wf758

dfinnegan, many thanks for explanation in layman's terms.

blake

This is quite true. Every once in a while, someone ventures onto the 996 board and makes these comments starting a holy war. The real issue with the 996/997 engine (wet sump) is that at high G's (track environment or brisk street driving) the engine can suffer from oil starvation. The end result = blown engine = @$12K expense. This had happened in numerous 996s (early 1999s especially) and supposedly has been "fixed" on the 997 with some pump assistance (though it remains to be seen).

I love the 964, and was quite pleased to hear that the TT/GT2/GT3 are dry-sump engines based on the 964/993 core. For that reason, I purchased a 996 GT3 and have been loving my track time ever since...

-B

SimonExtreme

I remain unconvinced that the list of problems are due to oil starvation! The problems that I am aware of include

RMS - leaks
Cylinder liners - break
Intermediate shaft - bearing failures

Only the last of these might be due to oil starvation and wet sump. having said that, I am not suggesting that all cars have these problems or even the majority. Some say it is a relatively small percentage but as these are the most numerous engines Porsche have built, there are a fair number of problems out there.

TR6

This is the Achilles heel of the E36 BMW M3's and MCoupes which are bullet proof otherwise. In fact, a lot of E36 guys add a little extra oil to bring the level up a little higher for track days to reduce the chance of starvation. But its a trade off as too much oil level can lead to windage problems (the crank whipping up the oil into a froth in the resevoir) and other damage. I don't know about the E46 BMW's. Maybe they improved the sump...

Dan V

All the Porsche literature I've read states "AIR COOLED". In fact my owner's manual warns that if the spoiler doesn't extend at 50MPH, you need to drive slower because the cooling will not be sufficient due to reduced airflow. (<-- finally got to use that smiley )

dfinnegan

I've often wondered about the air cooled vs oil cooled question.

I've noticed that with the oil cooler fan out, or, for that matter, an oil thermostat failure, I can still drive the car. It runs a bit hotter, but is still driveable.

While I've not had the fan belt break, I understand that if it does you can not drive the car. It simply gets too hot. For that reason I carry a spare belt.

In truth, I was of the opinion that they both contributed rather significantly, but thinking about it now I'm not so sure if the balance is 50/50 or more like 70/30.

Interesting question, but theoretically interesting at best.

Cheers

cgfen

[QUOTE=Dan V]All the Porsche literature I've read states "AIR COOLED". In fact my owner's manual warns that if the spoiler doesn't extend at 50MPH,
<snip>
_________________________________________________________________

very true
but
consider please that that is MARKETING literature/
i'd bet that if you discussed this with engineering types you'd quickly reach a consensus that these engines are oil-cooled with air circulation keeping oil temps within the desired range.

cheers

craig

blake

Let me chime in here:

1) If my 964 is purely air cooled, then why do I need 13 quarts of oil? I learned many years ago that oil is also needed as a cooling element in the 911 to reduce heat...

2) Regarding the 996, I have heard of numerous examples of blown engines due to oil starvation here on Rennlist. The current 996 board has a group of individuals that believe those blown engines were due to overly aggressive driving either on the street or the track. Just last week, it happened to my personal mechanics brother in his "new to him" 02 996. The engine blew up on the track and oil starvation was the culprit. My mechanic added that he makes very good money fixing blown engines in 996's and 986's (boxsters) that are out of warranty and used as track cars. He also noted that most of his customers run 2.0l through 3.6l "air-cooled" 911s and have very few problems. For me, those comments further solidified my belief that I will never take a 996 on the track unless it is CPOd (even then, be careful as Porsce might void the extended warranty).

Sure, these comments can be classified as stereotypes, but they are based on real-world experience. Unfortunately, we will never know the "truth" as Porsche will not be inclined to release that data.

IMHO, pick your next 911 based on need and reputation, and have a ball!

-B

Heirsh

To me either is acceptable. To say it isn't air cooled though (or shouldnt be called that) doesnt ring well in my ear.

An example:
There are fins on the sleeves and heads to take advantage of the air moved by the fan. I don't believe there is any oil running through the sleeve? (unless you count the oil these engines burn) The crankcase is definitely cooled by the oil, which is, in turn, cooled by the air.

To me it will always be an air-cooled engine with extra cooling provided to the oil to help when the direct air cooling isnt sufficient for places that the air cannot reach so well or keep cool enough.

Another way to think about it is did the engine design start out with oil coolers from the start or were they added later when the engine got too hot due to size and output changes?