RR

My car has a front and rear seal leak.
Brought it to the dealer to repair both, but District Manager has said that there is no guarantee that the car won't leak again.

Apparently - according to Porsche - it's the extra HP they are drawing out of the new motor that has caused this and that's why the old GT3 didn't leak. Something to do with the lessened drag or friction on the motor, honeslty I'm not quite sure how that works - wonder if it is synonomous to the crankcase breather mod for the 996GT3 that was good fro 5-10hp. Carnewal sold this, it was an RSR part.

They went on to say that most leaks they've repaired are all on cars that are not driven daily - whether you track the car or not makes no difference - if the car will be sitting for any length of time it will leak.

fc-racer

That's really disappointing For the record, I'm at 10,000km and no leaks, but that's not to say it won't happen in the future... fingers crossed...

ze_shark

The power/torque argument is kind of thin, isn't the 3.6 block identical to the Turbo ?
There was a credible explanation for why 996 Carreras would leak, and 996 GT3s/TTs wouldn't: block structure was different. But recurrence on 997 GT3s is really surprising. Perhaps we're looking at different root causes for the same symptoms.

340Elise

Yes, they are the same, but don't forget that the redline for the turbo is much lower than for the GT3. Now I don't know if the engine speed has anything to do with it, but I am just theorizing. What is the max engine speed of the 996 GT3?

Yargk

8200 rpm vs. 8400 rpm

GeoT3

I don't think crank shaft rpms has anything to do with RMS failures on 07 gt3s. Think about it. the rotating mass does not change in shape or circumference and if it did it would be less than 100th of thousand of an inch if not less... the rms seal should accommodate the difference.

I think the failure has to be in the design of either the seal itself or the devil may be in the crank case vacuum/pressure.

ze_shark

Yet, many were pointing at the 996 Carrera 3.4 and 3.6L blocks as having much lower torsional rigidity than the "GT1" block and therefore more prone to leaking at the far end of the crank. If torsional rigidity was at play, then one could speculate that the MUCH higher torque of a Turbo would make matters a lot worse.

Yargk

I agree, I was just answering 340's question.

Yargk

RMS is odd. I am sure some engineer at Porsche knows exactly what goes wrong, but the problem is any other information coming from people at Porsche who aren't engineers and think they know what is wrong. I can't say what the root cause is, but I've read enough to show me that most people don't either. Although GeoT3's "I think the failure has to be in the design of either the seal itself or the devil may be in the crank case vacuum/pressure." seems logical and simple enough that it might be true.

sjgreco

My 996 GT3 leaked twice, limited use had 6,000 miles in 30 months. I posted this response from Bruce Anderson before on a different thread, it seems to make sense of the cause of the current RMS leak issues.


I had never heard of this problem with the GT3s before. I had figured same old crankcase, same old seal, what can go wrong, they never leaked before. Since hearing from you I have looked into this and find that they have used a different rear main seal than the “Turbo” even thought they use the same crankcase. A GT3 seal (only GT3 not Turbo) appears to be installed "backwards" when you remove the flywheel. When you remove the seal you will find holes in the engine crankcase at the 9 and 3 o'clock positions (only GT3 not Turbo). These holes allow crankcase vaccuum to draw the lip of the seal tight against the crankshaft. (Again visualize the seal as being bacwards and the angle and face of the lip facing outwards instead of inward as would be normal.)

So, what we have are a few conditions that may not be favorable: The seal is really only very tight when the engine is running and there is good vaccuum. There is no check valve between the oil tank and the engine like the turbo has, so the only thing stopping the flow of oil back into the crankcase from the tank is the clearance between the gears in the oil pump.

Especially when they sit for extended periods of time, these cars may develop a slight seepage since the seal is not completely tight, and the oil level rises above the level of the two "ventilation" holes and accumulates in the compartment behind the seal (between it and the engine block).

Since a lot of owners don't drive these cars very much, (a lot of GT3RS cars especially), Porsche advises customers that under these conditions (sits for weeks without running), some seepage is normal.

Back when we had the "first" GT3 (996) - and this was actually the 2nd generation (Europe had a version with a different engine 1st, (ours was the 996GT3 F/L-facelift), there was a change to the seal. Porsche had more trouble with incorrectly installed seals than anything at that time - the Porsche techs saw a little seepage, thought the original seal was in backwards, and proceeded to install a new seal incorrectly (really backwards) that leaked even worse!

All this being said there was one change to the seal back a few years ago, and all the seals have been the same since. Porsche just released some new information in the spring about a "spacer ring" that fits between the seal and the crankcase and spaces the seal out to ensure a good compartment for the vaccum to build up behind and pull the lip tight. The seal itself hasn't changed.

All this being said, by nature of the design, and the laws of physics and huydraulics, some slight seepage under certain circumstances will happen.

It is normal to have light to heavy engine oil sweating (very light leaking) at the rear main seal (RMS) area of the GT3's, R's, RS's & RSR's because these cars utilize a very special double lip RM seal. This rear main seal is basically installed in the engine crankcase backwards and it allows the crankcase to breath giving the engine a small horsepower increase during higher RPM's and substantial load ranges.

PogueMoHone

^
Now, that's an explanation.

Great post.

Snowboarder54

Yes indeed! Thank you.