1998 E320 Oil Leak

[Cleverpig]

I need help identifying the source of an oil leak on my 1998 E320 Wagon with 145,000 miles. The oil is leaking from the lower right (driver's side) front area of the engine somewhere above/behind the A/C compressor and below the hydraulic pump. The leak has been very slow for a couple of years but has increased in recent months to the point of pooling in the belly pan and depositing several drops on the garage floor every day. I have confirmed it is engine oil (Mobil 1 0W40). The oil runs down the A/C compressor and drips off of it and the transmission fluid hose that runs adjacent to the A/C compressor.

Several years ago I replaced the seals on the valve covers and oil collection covers and these areas are still clean and dry. My independent MB mechanic recently replaced the seal on the oil pan thinking that might be the source with no improvement. With the A/C compressor and hydraulic pump in the way it is impossible to see what is behind them that might be leaking. It does not appear to be the head gasket. With air flow off of the fan it could be leaking from somewhere near the base of the oil filter canister and blowing onto the A/C compressor. After reviewing some older posts it sounds like it could be the oil test port cover gasket or possibly something behind the serpentine belt tensioner pulley assembly.

Any suggestions would be appreciated since the Cleverpig is stumped.

[Benztech]

Have you checked the oil pressure test plate at front cover just below oil filter housing it has 2 mounting bolts and a rubber gasket behind that is known to leak.Its updated with a new style gasket .The plate is about 3" by 2" square and has an oil press tap plug in cover. Tim

[Cleverpig]

Thanks Tim, I think you hit the nail on the head.

I purchased the seal and crush washer at my MB dealer today ($5.00) and just finished replacing the seal and cleaning everything up. The old seal had become quite hard. (The replacement seal was a different design so I had to cut the center out of it to end up with a rectangular ring seal like the one being replaced.) I removed the belt tensioner so I could clean and inspect behind it but found no problems there. It is all back together and clean as a whistle. I think that was my problem. I will inspect after a 150 mile trip tomorrow to hopefully confirm it is fixed.

By the way, I discovered a trick for replacing the serpentine belt or removing the tensioner. While using a long handled socket wrench on the large nut just below the pulley to rotate the tensioner (counterclockwise) to release the tension on the belt, insert a 1/8 - 3/16" allen wrench or drill bit (parallel to the pulley shaft) in the hole located on the bottom right edge of the tensioner mounting bracket. This holds the pulley in this position making it easy to remove and install the belt. The pulley must also be in this position to remove one of the screws attaching the tensioner assembly.

Hope this helps.