What is RMS?

Hello, I'm currently a 928 guy. I'm getting tempted by the declining market for cool cars and would dearly love to own another rear engined Porsche (have had a 964 and 993). In reading this forum I have seen mention of RMS failure in the earlier water cooled cars - 'sorry but what is the RMS? Any guidance on searching for/selecting a liquid-cooled, rear engine Porsche is greatly appreciated - I'm thinking of a Carrera 4.

Rear Main Seal...a known weak spot in these engines...

Do a search about them if you have two days to read everthing.

I thought it was R otten M uffler S yndrome....no wonder I never understood why everyone was so upset..

R esults of M obil S ynthetic.

Another 928'r, been here over a year, without Searching, asking about a 996. Come on.

The seal that seals transmission to engine. Common porblem with 3.4 engines, but after all, not a big deal. Easy to spot (oil under your car) and costs 500 euros to replace. It is the first time this newbie answers to a technical question about 996. Correct me if I got it wrong..

Try the search button for loads of info on the subject.

RMS - is the seal on the end of the crankshaft, which in all cars is at the transmission end. It does not seal the engine from the transmission. It keeps engine oil in the engine or at least that is the concept. My theory on why it leaks is that the RMS suffers from oil being slammed into it under braking. This doesn't happen it normal configurations because the RMS is facing the rear of the car and only endures acceleration forces which are a lot less than braking forces. Why doesn't the front seal leak on engines, they do. However their diameter is a lot smaller and they seem to only suffer wear and age related failures.

root mean square

Quotes source post: 6027299

sorry I have to step in and point out something here..Yes the seal is where you stated, yes the function is to keep engine oil in the crank case. HOWEVER these seals tend to leak from being poorly designed in the way the keep the oil on place, and or poor instalation, wear, fatigue, cracking, and presure build up in the crank case.... To even suggest that the oil gets by as the result of inertia from braking has got to be the worst explaination ever for the reason these leak.. To over come the seal via inertia would require your car to stop from 1000 mph in like 2 feet.... IMO there is no way braking could cause this seal to leak.... In the 60's and 70's Chevy 327/350/400 small blocks often had this same problem. They even invented a tool (sneaky Peet) to "thread" a new rear main seal in the block side of the crank so you didnt have to remove the crank shaft. The seal was basicly a piece of rope with some wax on it. I bet 10's of thousands of these done and yet no one seems to have ever spent this much time debating it...If it leaked, you fixed it... if it didn't...it didn't Often new seals have a reverse spiral double seal that causes the oil that gets trapped between the 2 sealing surfaces to be "corkscrewed" back to the block side. I have not seen the P-car seal, but this is not a major deal... it is just a seal, in a relatively hard place to replace and I doubt if it was ever the cause of an engine doing anything more than leaking a little oil and being a pain in the butt.....

My $.02. RMS leak is such a non-issue for most owners and when/if they do start to leak, the usual course of action is to wait until your transmission has to come off for a new clutch/flywheel. So if you know how to drive a manual transmission properly, you could wait a very long time to get rid of those pesky few drops of oil on you driveway! If you have a CPO warranty, then you get it done on their tab whenever you want. If you've owned air cooled 911's before, you should know what an RMS is since they have them too and YES they do leak on those old "bullet-proof" engines. I have friends with 993's who've had leaking RMS's. As far as reliability is concerned (saw your post on the 997 forum), the engine in the 966 MK2 AND 997 MK1 are almost identical and have about the same failure rate according to a service manager I know who also stated it is not as common an occurrence as the internet forums would have you believe. Do you really believe that Porsche would be the most profitable manufacturer in the world if the 996 engine was such a catastrophe? BTW: yes my RMS seal was replaced under warranty over 2 years and 35000 kms ago and has not leaked a drop since.

Ivangene, are you saying Porsche uses a rope seal like chevy did in the 60's ? also the reverse spiral is on the crankshaft not the seal. Have you ever worked on an engine ?

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now there is something I can relate to. funny in my older P-cars I was always tole the reason they leak is due to the high temps. and the expansion/contraction of the metals. this puts a fair amount of stress on the seals as you can imagine and eventually they give way. anybody have a 930 that didn't leak?

wross, I had an 911SC that I chased leaks on for years. I always saved spare cardboard for the garage floor. The drips were usually small and mostly annoying. Yes, I did suffer a RMS failure on my air cooled 911. It was pretty bad, but never did get to the clutch and I'm not sure it even could get there unless massive amounts of oil got by. The smell coming through the heat exchangers is enough to convince you to change the seal. Common Oil leaks on the aircooled 911's: *rear main *oil sender *engine oil thermostat o-ring *oil return tubes *"S" hose to tank *exhaust valve covers *through case bolts

Quotes source post: 6027750

No I am NOT suggesting that p-cars have a rope, I mearly stated that Chevy used a rope seal...and yes, you are correct the spirals are in the shaft, but I have seen them embedded in seals before as well.... yea, I have worked them....but spent thousands of hours wishing I never had.............

Kind of a "Renn" version of PMS; hence RMS. Affects a certain age group of 911, Boxters, and Caymans. Many of the same symptoms . .

At least RMS can be corrected...