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Old 09-05-2001, 10:09 PM
Jim W.
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Oil leak - 1978 300SD

We have a 1978 300SD with about 192,000 miles. There is a pretty good amount of oil that is leaking out of the top of the valve cover at both the connection fitting for the valve cover vent and the oil fill cover. The oil fill cover has been replaced with the "upgraded" cover with no improvement. There is not as much oil leak at lower speeds as at highway speeds. This leaking causes much oil to leak along the side of the engine and be wind blown along the underside of the car. Any suggestions as to the possible cause and remedies? Thanks for any help.

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Old 09-05-2001, 11:12 PM
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Join Date: Nov 2000
Location: Vernon, CT
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Now this may sound like an odd question regarding oil leaks, but what brand/weight oil are you using. Since I switched to Chevron DELO 400, my oil fill cap hasn't leaked. Recently though, when I drove to VA, needed to add some oil and used some Castrol, my cap started to leak. It seemed rather odd for it to just start leaking again. For the vent tube, you could try tightening the clamp around the fitting.
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Old 09-06-2001, 09:00 AM
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Jim W.

I don't know about the filler cap....a new one should have done it.

On the vent fitting, just buy a new one. Very cheap and available at your local mercedes dealer if fastlane does not have them. I also replaced the longer vent tube that goes to the top of the air cleaner and have no leaks at either end now. Rubber just gets hard when exposed to heat over long period (and may crack). Won't seal properly.

There is also a little bitty o-ring on the oil return line from the bottom of the air cleaner on my turbo 300CD that was the source of a very irritating leak. Cost about $1 and took ten minutes to fix that one.

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Old 09-06-2001, 05:21 PM
Jim W.
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Thanks for the tips. The brand of oil we have been using for several years, even before the oil leak problem became a problem, is Mobil Delvac 1300 15/40. It was a recommended product back when Mercedes was recommending particular types of oil.

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