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Old 08-19-2005, 05:39 PM
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Join Date: Dec 2004
Posts: 143
oil in air filter

I recently had some work done on my car. And I was at the indy's and the air filter needed to be replaced. I noticed that there was some oil on it. I asked my mechanic and he said no big deal. The car runs good but I'm sure the're shouldn't be oil in the air filter. Am I worrying about nothing or is this something that I should be concerned about?

Any input greatly appreciated

Tom in AZ

1985 300SD, smoke silver, blue interior, 146K
1973 280, 85K (sold)
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Old 08-19-2005, 06:01 PM
300SDog's Avatar
gimme a low-tech 240D
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Location: central ky
Posts: 3,602
On my '79 240D the valve cover breather tube runs into the manifold instead of the air cleaner.... so the intake manny is always wet but the air cleaner stays dry.

And inside the valve cover the breather tube runs through a chamber. I've loosely packed this chamber on mine with wide-strand stainless steel wool to collect oil from the vapors to then drip back into the valve train when the engine is shut down.
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Old 08-19-2005, 07:33 PM
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Location: Milford, CT
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The air filter in my 300SD was black from oil! It means you have blow-by, live with it. As long as the engine runs good you are fine.
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Old 08-19-2005, 07:58 PM
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And change the air filter every 30,000 miles, or every 15,000 miles if you drive in severe conditions like stop and go traffic, frequent short trips, long periods of idling, drive at high speeds in hot weather for an extended period of time, driving more than 2,000 miles a month, etc...
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Old 08-19-2005, 08:03 PM
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Join Date: Sep 2004
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Thumbs up

I have a little bit on the bottom of mine too. As I understand it's normal too.
I'm not a doctor, but I'll have a look.

'85 300SD 245k
'87 300SDL 251k
'90 300SEL 326k

Six others from BMW, GM, and Ford.

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Old 08-19-2005, 08:48 PM
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Join Date: May 2005
Posts: 992

on top of your engine there is a rubber pipe that goes to the
air filter... this pipe acts as mercedes pcv valve which is crank case
ventilation.... on a volvo they call it a flame trap... and what is
suppose to happen is as you drive your oil turns into vapor and
this pipes the vapor over to a trap inside the airfilter then it turns back
into oil and flows back into the engine.... but once a car gets over
say 100k miles the rings get a little worn and the vapor turns into actual
oil... and the oil leaks in around your air filter....

on the one hand when i was a kid and rode motorcycles we use to soak our air filters in oil on purpose it catches more dirt that way... on the other hand it is a symptom of wear but you still are a very long way away from new rings.

I have oil in mine....just change your air filter or rotate it ever few months..
or you could make a bypass and use a pipe to get the oil back down without going through the air filter... but you do not want to block this up because if you plug the hole then you will create preasure in the engine and it will blow out your seals and you will be leaking out the front and rear of your engine..

I have started using synthetic oil and I dont believe it turns into vapors so I am questioning this as well...
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Old 08-19-2005, 09:44 PM
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Join Date: Jun 2004
Location: West of Ft. Worth. TX
Posts: 4,170
On my SD, I found there were a couple of things that helped to alleviate, although not eliminating, this problem.

Make sure the oil drain tube coming from the bottom of the air cleaner has good o-rings. (Ensure the air filter housing mounts are good also.)

Also, the next time you do an oil change, run some "engine oil flush" through that same drain tube. (There is a check valve at the bottom, in the upper oil pan, that gets a lot of dirt and grit in it.) (Do a search for "oil flush and check valve" and you should be able to find a photo, if you would like.)

I believe DMorrison replaced that check valve because, after some testing, he found that was where the oil appeared to be coming from. A little oil won't harm anything, "oil-burners" aka diesels run on that stuff.

84 300SD 350K+ miles ( Blue Belle )
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Old 08-19-2005, 09:49 PM
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Join Date: Aug 2005
Posts: 22
I changed my filters a few weeks back in my 300SD, and it was coated in oil! My breather hose was also on its way out, so maybe that had something to do with it.

Right now my baby is cranky because I haven't taken her on a long drive in a long time. She hates idling!
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Old 08-19-2005, 10:18 PM
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i think

i think the syntheic oil does not become vapors.... so....
this is to be considered.
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Old 08-22-2005, 01:19 PM
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This forum is great

Thanks for all the response..
Tom in AZ

1985 300SD, smoke silver, blue interior, 146K
1973 280, 85K (sold)
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Old 08-22-2005, 05:42 PM
skydivetoday's Avatar
"My Dog House" Yanmar
Join Date: May 2004
Location: Marco Island, FL
Posts: 87
I think SD Blue may be right.

I have old engine,

I use Mobil 1

and I have never had oil in my air filter

therefore I think Sd Blue makes sense.


In scuba diving and skydiving as in life, if it isn't fun, your doing it wrong.

Original owner & daily driver, 1983 300SD 298,000 miles.
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