The W123 chassis covers 240D's, 300D's, 300TD's, 280E's, and several other models of Mercedes coupes, sedans and wagons from model years 1977 to 1985.

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Why is there oil inside/below the air filter housing?

recently looking for oil leaks on my MB 300D w123 I realized that under the air filter housing around the hose that comes from the motor head, there is a lot of oil as well as inside of it at its bottom. Where does it come from?

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I had the same problem with my 240D. Took it to a mechanic who should know these cars and he said the engine was shot producing the blow-by. Then I found a statement on the web that the vacuum pump would leak oil when it's diaphram or check valves were faulty. Bought two repair kits for $35 (new diaphram and check valves) and rebuilt the pump in about two hours and that stopped the oil leaking into the air filter housing. Be careful with those bolts as the allen head can become rounded all too easily which is why it took me two hours instead of one. Had the valves adjusted and the engine is fine. Starting off on my second quarter million miles now :~)

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Tom, good comment. It's important to note however that the diaphragm style pumps that can pump oil in to the air cleaner are only on the early W123 cars. I believe no later than 1980. So if the original poster has an older W123 this would not be possible in their situation since they would have a piston style pump that vents internally, in to the crank case; it does not have a vent hose going to the air cleaner like the early style. Just wanted to mention this before potentially sending the OP on a goose chase for a way for oil to get from his vacuum pump to the air cleaner on a later Benz :)

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hjoab, it comes from your crankcase breather pipe. That is the hose coming from the valve cover to the airfilter. You seem to have to much blowby which forces the oil out into your airfilter. Now it will seriously depend on how good your mechanical skills are and what tools you will have available. Do a compression test to see if you have a problem with a ring and consider a leakdown test as well These tests may be needing to be done through a proper garage. Hope this helps, good luck.

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On my relatively simple 1982 240D (manual transmission)...

oil collecting under air breather ... and, it turned out, 95% of oil dripping, over time, onto garage floor ... was solved by 2 extremely simple fixes:

the rubber elbow under, and therefore inaccessible short of removing air filter housing,

was cracked and "weeping" oil...

Not even having a new one on hand, a quick fix was to exchange it with the one on top so as to be able to quickly replace it when I got a new one.

AND, 2nd ... the oil filler cap was also weeping oil...

I experimented and finally went with a FUEL filler cap / nice shiny chromey FUEL cap--they ARE interchangeable, SIZE-wise at least.

The FUEL cap on the OIL filler worked so much better/tighter than what was also around $5-$8, an all purpose oil filler cap -- on both 240 and 300D.

(And, yes, I also, in this process, bought a replacement GASKET--fitted it...it wasn't as oil-tight as the new FUEL cap. By fuel cap I mean the standard, all purpose one you find in places like OReilly's...chrome color/rugged looking with squared ridges the new oil filler cap which felt like a black plastic toy relatively.

On 300D ...... more complicated but it SOLVED the problem:

open up air filter housing ... just study what's inside.....

that unit that's the size of half a soup can, black plastic with 2 metal tabs holding a round "end" to the "soup can" .... I found instructions online elsewhere to: put gasket material around the edge, seal it up (relatively)...carefully, with hammer and screwdriver for example, tap those metal tabs back down.....thus creating a more oil tight unit, tighter than it was before adding the black gasket stuff around the top edge ($1 at 99 Cents Only).

.....when we got this 300D at 169,000 mi, 1983, not knowing its history...air filter was lousy with oil, 2/3rds the way around ...... subsequently, after tightening up, as described above, and cleaning out with paper towels of course the whole housing...new CHEAP air filter (expecting to use them up faster than the nice Mann German ones)....was CLEAN after 1000s miles of driving. With no oil collecting inside the housing.

If you have oil dripping onto floor also ... wearing gloves is awfully handy for this ... reach under the 300D housing, feeling for a tube that drains downward to a connection WAY low on the engine ... hard to see--usually covered with oil etc...

this tube you're feeling for is light weight, with curves, total length circa 1- 1 1/2 foot...these connections of this light weight oil tube are just a bigger tube fitting over a smaller nipple / tube--not screwed/gasketed or anything--and can come disconnected...(it might have an O ring come to think of it but point is, you just thunk it over the smaller tube and it's connected nicely.) Feel for it and you'll know what I mean. It was a dripping mess before I figured it out--connected it, rag-cleaned engine...now fabulous.

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my vacuum pump diaphragm keep on braking on the same place after 4 to 5000 km .can you advice ?

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hjoab will be eternally grateful.
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