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Bad rear main seal[240-260/88] posted by Lujo Bauer on
Monday, 15 June 1998, at 7:43 a.m.
Hi guys. What causes a rear main seal (1988 240DL B230F) to go bad? Mine is due for replacement, but I'd like to know that the new one won't start leaking, too. I don't think it's the flame trap, if that even could be the problem.
Thanks,
-Lujo
Re: Bad rear main seal[240-260/88] posted by Don Foster on
Monday, 15 June 1998, at 8:01 a.m.
Lujo ---
My experience (I now have 4 240's, and 4 others in my past) is that age and miles take their toll. You can expect to need a rear main at about 200k miles, more or less, if the car has recieved reasonable car and oil changes.
On rare occasions, a seal will pop out of its seat, and you'll have a real mess. (I had this happen to an '83 at 125k -- it now has 290k.)
However, if the flame trap has become plugged and/or the associated vacuum lines are plugged, the crankcase builds up pressure and will push oil past a working seal.
Here's my "jiggle" test: With the engine idling, loosen the oil cap and let it rest in it's hole on the valve cover. If it bounces around and jiggles, you probably have too much pressure -- the PCV system may not be working well. If you do have vacuum in the crankcase, the cap will be pulled down and won't jiggle. There's a small vacuum line from the flame trap assembly to the intake manifold that is often overlooked, and plugs easily.
Incidentally, if the problem is a bad PCV system, the front seals are likely to also be seeping.
--
Don Foster