1989 Mercedes Benz 300e engine oil leaks

  • 1989 MERCEDES BENZ 300E
  • 6 CYL
  • 2WD
  • 164,516 MILES
This vehicle has a rear main leak and oil pushing past the oil fill cap. Someone else replaced the front cover and oil pan to remedy those leaks. 3 rear seals have been installed by another tech at this shop to no avail. I should note that it was only a seep at the rear main before replacement. Crankshaft run out is less than.005 of an inch. This vehicle builds up to 18psi of pressure in the crankcase on moderate to heavy acceleration and remains in a pressure situation until the throttle is released at which point it returns to a vacuum of 16 inches. Pcv has been inspected and is clear, it also has vacuum to it. Leak down tests show less than 5%, compression tests are good at 190psi cranking. The vehicle runs fine. Any ideas would be great. Obviously I am missing something.

thank you. Craig
Do you
have the same problem?
Tuesday, April 13th, 2010 AT 2:45 PM

1 Reply

Engine mechanical condition can be checked using a compression gauge, vacuum gauge, or an engine analyzer capable of performing a relative compression test. See engine analyzer instruction manual for availability and description of relative compression feature.

If a vacuum gauge is used, connect it to intake manifold vacuum. Observe vacuum gauge. Open throttle part way and hold steady. If vacuum gauge slowly drops after stabilizing, exhaust system should be checked for a restriction.

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CAUTION:Use a remote starter to crank engine during compression test, NOT the ignition switch. The fuel injectors on many fuel injected models are triggered during the cranking mode. This could cause a fire hazard, flooding, crankcase contamination, hydrostatic lock, or lubrication to be washed off of cylinder walls.
The exhaust system can be checked with a vacuum gauge or a pressure gauge. Remove O2 sensor or air injection check valve, if equipped. Connect a 1-10 psi gauge and run engine at 2500 RPM. If exhaust system backpressure is greater than 1 3/4 - 2 psi, exhaust system or catalytic converter is plugged.
Crank end play should be between.002-.009, is this what you were referring to? PCV system may be clogged, this would allow excess pressure as well.
As engine RPM increases, vacuum decreases.
Either the PCV isnt working, or the compression rings are worn. Any blue smoke out of the oil filler pipe?
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Tuesday, April 13th, 2010 AT 3:24 PM

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