At last, RMS failure prevention explained?

So I'm eating my lunch and reading some articles on the internet when I stumble upon this gem on The Engine Oil Bible . I'm actually reading it because I want some more information on what weight of oil to use and how regularly to change it. Something that caught my eye was Chris' discussion of checking and topping up engine oil levels. So I'm reading along and wham-mo: he mentions the rear main seal, and this isn't even a Porsche forum. To save you the trouble, here's the relevant quote and photo (at bottom of post) from the site (I've taken the liberty of highlighting the very noteworthy portions): " Checking the oil in your engine, and topping up. " "To a lot of people, this little section could be categorised by the rearranging the words "granny eggs teaching suck your to". But you'd be surprised by the number of people that don't know how to do even this basic task. When checking the level of oil in the engine, the car should be on a level plane, and should be relatively cold. I've run into several people lately who insist in keeping the crankcase topped off completely, and they invariably check the dipstick just after shutting down the engine. Now look at this image, and then read on." "Reading the oil in this way results in an erroneous reading because a quantity of oil (usually about half a litre) is still confined in the oilways and passages (galleries) of the engine, and takes some time to drain back into the crankcase. On the image, the blue areas are where oil is likely to still be running back down to the sump. But on seeing what appears to be an abnormally low level on the dipstick, these buffoons then add more oil to the crankcase. The oilways and passages all empty, and suddenly the engine becomes over-filled with oil, going way above the 'MAX' mark on the dipstick. The problem with this is that the next time the engine is run, the windage in the crankcase and other pressures generated by the oil pump, etc. place a great strain on the seal on the rear main bearing. " " Eventually, often much sooner than the ordinary man in the street might expect, the rear main bearing seal ruptures, and the engine becomes a 'leaker' . If you've got a manual gearbox, this means one thing: this oil goes right onto the flywheel and the face of the clutch disc. A lubricated clutch is A Bad Thing." "If this still goes unnoticed, the front seal is the next to go, and the engine then becomes a 'gusher'. As well as smothering the clutch with oil from the rear, the oil now coming from the front leak will be neatly distributed about the engine bay as it hits the front pulley - often propelling it out as far as the brake discs. It's sort of like a Hollywood disaster movie in the making, yet people don't consider this." SO, MY INTEREST IS THIS: Could the reason that some Porsche owners are experience RMS failures is that they are all TOO OFTEN overfilling the crankcase with oil? I mean, given that Porsche owners are a doting lot, could their over-attention to proper oil levels actually be contributing to the RMS problem that has been plaguing this forum for ages? Ahem, let me be specific: Bob, do you put too much oil in your engine? Might this potentially account for RMS failure? OR, am I reading something wrong from this site? And if so, I am really very sorry for bringing up this issue again, but I thought the notion of overfilling the crankcase as a potential cause of RMS was a pretty interesting hypothesis and would love to hear everyone's thoughts. Cheers fellows.

Hmmm. The manual says to check the oil at temperature, and the gauge gives you a countdown to when it is ok to check. I however, don't trust it and always check my oil when the engine is cold, because I do agree that a half liter under is way better than a half liter over. I will point out that the "blue areas" in the 996 engine are in different locations than in the diagram.. the cams and covers are on the side, not the top, but that probably means they drain slower. What isn't clear to me is the mechanism for a small amount of oil to greatly increase pressure on the main seals. In an engine like the one above, 40 psi is a lot of oil pressure. The 996 runs at about 4.5 bars, which is about 150 psi. don't know if any or all of that is exerted on the RMS.

Nah I don't buy it. First off, the way you check your oil in a Porsche is entirely different to other engines. The flat 6 layout is entirely different. You run the engine to normal operating temp then let it sit for about 20 minutes on a horizontal flat and level surface. This lets all the oil drain down to the bottom of the pan so a more accurate reading can be made. The digital oil readout is apparently the most accurate but I check the dipstick too. If the oil is still draining the readout will tell you how long yu must wait before it will give you the answer. Too much oil in a 996 is not good but it will no more cause the seal to blow than the usual engine operating pressures which are very high already. If anything too much oil will cause you to burn it off in a plume of white smoke. So 2 things. 1) measure your oil when the engine is hot not cold. 2) overfilling wont cause the seal to blow out. There is one other point in regard to overfilling. There is overfilling and OVERFILLING!!!. A little too much say a qrt is probably no harm but don;t do it again. A top up until it overflows is just plain asking for trouble.....likely a fire even!

So 2 things. 1) measure your oil when the engine is hot not cold. 2) overfilling wont cause the seal to blow out. Based on my limited empirical experience, I would have to agree. Many years ago I bought a Vette and the Dealer agreed to give me my first oil change for free. It turned out that the jokers overfilled my crankcase by about a quart, and I didn't notice it until about six weeks later when I checked the oil level. Anyway I kept the car for over eight years and 120K miles, and there were absolutely no leaks. Even after 120K miles there was no detectable oil loss.

Regarding oil levels - it is true that the oil in a flat configuration engine can take longer to drain and allow accurate readings. However I haven't had that problem with the 996 - it gives consistent readings whether cold, warm or hot. Perhaps the angle of the oilways and shape of the sump help, or the oil viscosity even. Now my previously owned BMW flat twin bikes were another story - you could never get a consistent reading, particularly on the oilhead! If you wanted a different reading, just leave it alone for a few days and check again. Not a problem with the 996 in my experience.

Slight conversion error: "The 996 runs at about 4.5 bars, which is about 150 psi." 1 bar is 14.5 psi. 4.5 bar is 65.25 psi.

Thanks. I got the number 33 from scuba class = 1 ATM. I need to go figure where I went wrong (after lunch).

33 feet for salt water, 32 feet for fresh water... just to be a dick.

Riad, You succeeded. (Just kidding). But thanks. I had lunch and never had to look it up. 33 feet of depth gets you 1 bar. PS... wanna do a weird fresh water dive... check out Homestead Crater in Utah.

I recently had my oil scavenger pump replaced (had a couple of drops of oil, hope it isn't RMS, none since) and I was wondering -- what does a scavenger pump do? The only image I could come up with was a pump that somehow recovered the oil distributed in parts of the engine once it is shut down? I know that is probably waaay off, but thought maybe the presence of a scavenger pump would change the way oil is measured in a Porsche? Signing off, Ignorant non-gear head

I've been diving for about 20 years, although I haven't been in a few. I'm a certified PADI Rescue Diver, I've done lots of cool fresh water dives, the best part being you can crack your regulator and take a quick drink when you get dry mouth. But this is beyond off topic.

In most engines the heads are vertically above the oil pan, etc. The oil that's pumped up to the rockers and/or cams drains back down by gravity. And on it's way back gets whipped up by the spinning crank. In the M96 engine, the oil at out the heads used to lube the valve train is pumped back into the crankcase. That's what the scavenge pumps are. Bill