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0W-40W oil link to RMS leakages?


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Folks, after reading a lot on the new Porsche 0W40 engine oil approvals, which appears to be a move to have a global engine oil, and avoid the need for a seasonal recommendation, I am thinking there may be a link to RMS leakage and ultra low engine oil viscosity.

I use Mobil 1 15W50, and have done so since reaching the 1,000 mile mark on a 40th Ann 911. I see in the owners handbook that 15W50 is acceptable when ambient temp. is 50F or higher. I live in Chicago and store the car in the cold months, so running below 50F is not an issue for me.

My experience many years ago as a mechanic, when low viscosity oils were becoming more prevalent, was that seal technology had to change, particularly for the crankshafts and front/rear timing covers due to the fact that the thinner oils had a marked tendency to weep past standard seals. Labyrinth seals for the rear crankshaft journals were commonplace to combat this particular situation, and had to be very carefully installed etc.

I am wondering if any others out there have an opinion on this, and particularly if users of higher viscosity engine oils have experienced less/no leakage past the RMS vs. the owners who have strictly used 0W40. Maybe those of you who have workshops would have more evidence - either way.

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My theory is that winter stored cars are more prone to RMS since no lube for months during storage. I believe there are RMS cases for daily drivers so my theory isn't 100% proof.

If your theory is true, would RMS stop if you just change to thicker oil?

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In general a ticker oil would prevent some seepage from the RMS. On that note though you could never go back to using thin oil. There were lots of problem on older 911s that leaked oil when switch to synthetic. The reason stated that synthetic molecules are smaller and can get by the seals. Also some had theories that synthetics don't allow the old seals to swell and stay tight. It could be that the thin oil and a rubber not designed to work well with synthetics maybe the reason there are so many RMS leaks.

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My theory is that winter stored cars are more prone to RMS since no lube for months during storage.  I believe there are RMS cases for daily drivers so my theory isn't 100% proof.

If your theory is true, would RMS stop if you just change to thicker oil?

It is not so much as a 100% theoretical fix that thicker oil equals zero RMS leakage, but I think that ultra low viscosity oil could be a factor. I understand there have been 996 and Boxster case machining issues that did result in a slightly out of round condition where the RMS sits, resulting in an elliptical shape of the seal vs. the perfectly (almost) round crankshaft seal journal. What I can see is that the case suppliers use sophsticated machine tools and statistical process control to make sure that cases are bored and finish machined to exacting tolerances. The logic that the case tolerances are still flawed seems a bit of a stretch to me, and the fact that 0W40 engine oil starts out with a viscosity that is so low may be part of the problem. I also acknowledge that seal designs have improved dramatically over the years, and I have to assume that the RMS seals used by Porsche would/should be as technically advanced as the 0W40 oils they approve.

I just think there is more to the RMS story other than dimensions and replacements that seem to continue to leak. People are still having the problem after all these years of reports - and from what I understand by reading the PCA website, we are, at this point, not sure if the 997/997S is immune.

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Do you really think M1 0W-40 is the issue rather than engine assembly specs? I have used M1 for 3 yrs on my 02 Cab and no leaks....and that is with storing it for 3 months in the winter. However, just to be safe should I switch to a higher viscosity synthetic? Car is stored in an insulated garage that does not get below about 35 regardless of outside winter temp.

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I thnk some people are desperate to find an answer to the occasional RMS leak, and I don't think the weight of oil you use has anything to do with it.  JMO.

I am deperate (6 RMS replacements and 7 seals). But I have always used mobile0/40.

I can pretty much guarantee that a RMS replaced on my engine will show signs of leaking at between 200 and 300 miles after the seal is replaced. The leak starts off slow and then max's out to about 4 drips per month.

imho, the oil isn;t the issue. My theory on it is that the seal only leaks when the engine is hot and cooling down. So a car that is garaged may leak once when it was parked up (the engine hot) then never again until the car is driven again and parked up to go cold. As the engine coos, the block and seal contract/constrict whatever. Sometimes this leaves the engine block halves twisted ever so slightly. Sometimes they go back into shape. On my car, the bore hole was once measured out of tolerence, then in tolerance, then out of tolerance and so on. I have sen this measured myself in disbelief. If it's out of tolerance then it leaks oil. SImpe as that. The only real way to not have an RMS problem is leave the engine running :lol:

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  • 3 months later...

I used to worry quite a bit about RMS until I realized that RMS is an issue on many engines made by many manufacturers including the engine in the V8 Lexus LS400. I hope I don't suffer from RMS but at least I know what to look out for and catch it early if it happens.

Bobby

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I am new to Porsche, so please forgive the stupid question - but if it maxes out at only 4 drops per month - is this really a major problem for the engine itself - or just more of an annoyance at having such a nice car that drips oil on the garage floor?

Thanks,

Kirk

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The RMS leak is more of an annoyance - Especially after spending so much money on a P-Car...

If the seal ruptured you could lose a lot of oil fairly quickly and possibly cause engine damage if you happen to be pushing the engine at its limits at that moment in time. Having said that - It is extremely rare that the seal would totally fail this way

If only small amounts of oil are lost then it just makes it a problem for your garage floor and the cleanliness of your crankcase.

If you are losing a fair amount, then some oil may find its way onto your clutch plates (splashed up via the flywheel) which would then require you to replace those clutch plates.

Most people do not experience an RMS problem yet on the other hand there are a few folk which have had leaks even after having the seal replaced a number of times which tends to make them rather annoyed!

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