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Old 04-08-2008, 06:59 PM
Registered User
Join Date: May 2006
Posts: 3
Oil leak from filter housing (expanding O-ring)

Hi everyone,

I just did oil change on my 99 SLK 230 yesterday and used a new filter kit from the dealer. After I was done, I started the engine and it all seemed ok. After running the engine for about a minute, I noticed oil leak from the O-ring. Turned the car off and dried the area. The O-ring had a bulge at the area where the oil appeared. I removed the cap and made sure all is in the right place. The O-ring seemed as good as new. Replaced and tightened the cap a little bit more that a hand-tight. Inspected the O-ring and made sure there are no bulges. Started the engine again. No leaks for about a minute, but as soon as started warming up it started tearing up (see pics).

It almost seems like it is building pressure and pushing the O-ring outward.

The only thing I can think of is that at the time I replaced the filter, the housing looked really dirty, so I used a long screwdriver and a rug to clean it up. I noticed two valves/sensor looking things at the bottom of the oil filter housing. I hope I did not damage any of them...

What are those two things and how can I test they are still functioning? Any idea why it is building pressure from the inside?



P.S. I used a brand new kit from the dealer - filter and O-ring. At the time of the install I made sure the new O-ring is seating right and tightened it about 1/4 turn with the wrench more than hand-tight. It looked nice and evenly pressed on all sides. After running the engine for about 1 to 2 minutes, I actually noticed an oil spot on the floor and more of a slow stream of oil coming down from a different bulge. Stopped the engine and cleaned the area with brake cleaner spray. Removed the cap, dried and inspected the O-ring, replaced the cap (1/8 turn with the wrench) and verified the O-ring is not bulging. This time I actually just stared at the area for about a minute and then I watched the O-ring deform and bulge before any oil came out. I shut off the engine right away before taking the pictures, that's why it shows just a little bit of oil. Cleaned the oil again and took another pic to show the bulge.

I will try to take more pictures from different angles and from inside the housing.

I do believe it may have something to do with the filter bypass and drain back AFAIK... I may have damage them with the screwdriver...

What effect will they have on pressure if both are fully closed/clogged up? Can they be replaced?

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Old 04-08-2008, 07:56 PM
Larry Delor's Avatar
What, Me Worry?
Join Date: Jun 1999
Location: Sarasota, Fl.
Posts: 3,114
This may sound silly, but....where is the old o-ring? What you describe usually happens because the old o-ring is still on the cap.
It is a truism that almost any sect, cult, or religion will legislate its creed into law if it acquires the political power to do so. Robert A. Heinlein

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Old 04-09-2008, 12:22 PM
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Join Date: May 2006
Posts: 3
Old O-ring is in the trash. I have done a few oil changes in my life before, I'm not a virgin when it comes to working on Mercedes, I owned 17 different ones over the last 14 years.

The issue here is something more serious,

If anyone can provide me more information on the valves at the bottom of the oil filter housing, it would be greatly appreciated...

Is it possible to remove or replace them? How do I test them and/or clean them up?

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Old 04-09-2008, 07:23 PM
Johnhef's Avatar
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Join Date: Feb 2005
Location: Frederick, Md
Posts: 4,540
Where are the pics? It sounds like it's still not being tightened enough, "hand tight" can vary greatly. You need to turn the filter wrench to where it gets snug then maybe 1/8th of a turn past that.

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Old 04-10-2008, 12:48 PM
cf cf is offline
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Join Date: Aug 2000
Posts: 51
Sorry I do have not the same car but I have a question:
are you supposed to see any o ring at all after the filter assembly is screwed down?

Could there be something in the filter housing preventing the proper insertion & seating of the filter element?

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