I just changed my oil tonight, and went to inspect the two o-rings on the rod that runs down inside the oil filter. They weren't there. The only reason that I know that they should be there is because of this discussion board, but they are neither present nor accounted for. What do they do and how bad is this. God only knows how long they've been gone. . .

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1982 240D - 292,000 miles and counting
Same family for 33 years
Newly rebuilt Monark injectors
Newly replaced clutch
New Bilstein shocks

I have tried on this one as well. My personal explanation (based on the FSM alone) is that they seperate the finely filtered oil from the oil in the filter chamber.

mine were wasted as well. After replacing, I perceived no difference - this means nothing.

But the finely filtered oil goes through the shaft connected to the cap and into the pan. The filter chamber has a fair amount of pressure in there and it would not take much to contaminate the filtered oil considering that pressure obove.

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I agree with jt20. They are very cheap, 6mm x 10mm x 2mm, if memory serves. Most every auto parts store should have them.

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83 SD

84 CD

Don't use plain rubber orings, they will deteriorate quickly in hot engine oil. Viton is the material for this type of application - make sure you get the o-rings from the air conditioning selection in the auto parts store - they are generally green or brown, and generally are made out of viton to live with refrigerant and compressor oils.

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95 E300 Diesel 265k and counting

I changed my oil and filter this last week. I had bought several filters at one time years ago so I thought I was ready to go. I really can not believe these filter manufacturers would sell these car specific kits WITHOUT putting those two tiny O-Rings into the kit... it has the copper washer for the drain plug.... the oring for the top of the filter canister... but NOT these orings.
I am dealing with a Honda brakes and transmission at the same time... so I went to the Van's in Austin ( taken over by CarQuest) and it has a Carpack in the same building.
They could not find a number for these rings.... so had to find it by size ( thanks to the forum I had that written down ) ... they had them... but they are black. I would be worried about a generic oring from Ace Hardware.... but am hoping a 'car place' when asked for an oil oring would only have the proper type rubber orings to give to customers... but the statement about green or brown worries me.... is Viton not available in Black ?
I hope more discussion and information will be forthcoming in this thread.

I'm sorry - didn't mean to alarm you - it is quite possible that the viton orings are available in black as well - in my experience (which is certainly not universal) when looking in the "ac oring" box, they are usually green.

I'm with you - I'd think o-rings from a car place should all be viton.

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95 E300 Diesel 265k and counting

I bought some of these O-rings from Phil at Fastlane about a year ago, and they're black. I inspect them every time I change my oil and they haven't deteriorated so far.

I plan to change them about every 6 oil changes, since the heat will eventually harden them.

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'81 300CD - 180K, cannot be killed by any conventional means
'99 Ford Escort - good MPG

I am not alarmed... but if there is the possibility the others need to be installed it will certainly be easy to pull the center and replace them... I only drive my car a few hundred miles a year and do not depend on it for transportation.... I do believe what the FSM says about them being important... so getting them correct is just one thing off my worry list.

There is no such thing as a "plain rubber oring." The commonly sold open stock 0-rings are Buna N, which is rated for use in petroleum products up to 250 degrees F.

Ok, lets narrow this down. By ' commonly sold' are you assuming a car parts store ? Is there any possibility that at Ace Hardware they have some rubber open stock orings used in plumbing which would not be Buna N ....and thus should be avoided inside our engines ?
Thanks, Greg

the oil filter thermostat reaches the full open position @ 125*C thats 257*F

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LOL, Good Catch ! of course that does not mean the temp does not get hotter than that opening setting... so we do need to work out the details of the proper oring material to be safe.

ditto

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Buna-N will work fine in hot oil but will eventually harden (the ones in my 123 had turned to hard plastic and actually snapped in two when I tried to remove them so I could install the new ones. Buna-N o-rings should be changed every year or so; Viton will last longer but you still should check them at every oil filter change.

Don't assume anything about o-rings when you buy them. If they are not explicitly labeled "Viton" (and priced accordingly) you should assume that they are Buna-N. Color may or not mean anything – again, don't make assumptions.

Jeremy

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"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970

I went to my local Mercedes dealer to get these two O rings and the parts assistant manager told me they didn’t carry them because they were not really important
It appears that on my ‘95 the two O rings are sized different…the top one is sized slightly larger than the bottom one. Anyone knows what these sizes are?

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1995 E300 Diesel
2002 GMC Duramax CC LB 4X4