(M110) Oil accumulating inside intake manifold? - PeachParts Mercedes-Benz Forum

rbtoj · #1 01-09-2017, 11:39 PM

Hi everyone,

I'm currently fixing the CIS fuel injection system on my 280 SLC, and upon removal of the air metering unit, I noticed that I have a small puddle of oil inside the intake manifold, just after the throttle body (see pic).

Is this normal for a 45k mile car, or do I have a problem?

(I do not have any blue smoke or other symptoms of burning oil).

fonzi · #2 01-10-2017, 08:14 AM

I believe the way the oil gets in there is from blow-by, and vaporized oil getting sucked in via the positive crank case ventilation. This is much more apparent on my w126 where the hose comes right off the top of the valve cover and attached to the air cleaner. I'm honestly drawing a blank on where the positive crankcase ventilation is on a 107 m110 even though I have owned several.

meltedpanda · #3 01-10-2017, 10:28 AM

it is not normal , how often do you drive the car? I assume filters are clean , PVC functions, not clogged?
Do you have any oil seepage along the valve covers?

rbtoj · #4 01-10-2017, 11:22 AM

The car is driven about 1k miles per year, for 15 years now.
Oil changes are done once a year, and I have no seepage on the valve cover (but I do have that dreaded leak in the front of the valve box gasket - new gasket on the way).
Filters are ok.

According to the service manual, my engine (M110.986) does not have a PCV valve per se, only a passive passage for the oil vapors.

I'm thinking this could be related to a rich mixture problem that I'm chasing for the past 8 months now. According to my research, unburnt fuel can get to the sump. Perhaps this is wreaking havoc on the PCV system, leading to my problem?

meltedpanda · #5 01-10-2017, 02:14 PM

hmm, well it may be "normal" for your engine, meaning if not driven a lot , I suspect it may not "burn off" some of the normal blow by which then just accumulates.

Is it wet or dry? Just notice it or has been it been there awhile. What about plugs , are they burning clean ?

Unburned hydrocarbons can be black , but dusty like and not oil like...
Just throwing out ideas

rbtoj · #6 01-10-2017, 02:55 PM

The spark plugs wont be a reliable diagnostic tool in my case. Because of the rich mixture problem, I clean them very often (carbon build up form the excess fuel). I haven't noticed oil build up on them.

And yes, the oil is wet. Is a puddle about 2mm deep.

However, I have found that the vacuum hose form the intake manifold to the WUR was disconnected (it's old and dry), and perhaps this may affect the ability of the engine to suck the oil back into the combustion chambers (because of less vacuum).

On a side note: whoever the engineer is at Mercedes that thought that putting all those air/vacuum hoses on the most inaccessible place possible was a good idea, deserves to be shot!

meltedpanda · #7 01-10-2017, 07:09 PM

you may be onto something there,
and
bloodied many a knuckles in the engine bay of my 107

Frank Reiner · #8 01-10-2017, 07:44 PM

Quote:

Originally Posted by rbtoj

The spark plugs wont be a reliable diagnostic tool in my case. Because of the rich mixture problem, I clean them very often (carbon build up form the excess fuel). I haven't noticed oil build up on them.

And yes, the oil is wet. Is a puddle about 2mm deep.

However, I have found that the vacuum hose form (from?) the intake manifold to the WUR was disconnected (it's old and dry), and perhaps this may affect the ability of the engine to suck the oil back into the combustion chambers (because of less vacuum).

On a side note: whoever the engineer is at Mercedes that thought that putting all those air/vacuum hoses on the most inaccessible place possible was a good idea, deserves to be shot!

The rich mixture is likely caused by the WUR responding to atmospheric pressure through the disconnected manifold pressure line. That feature of the WUR is specifically to provide enrichment at large throttle openings, and the resulting increase in manifold pressure.

The EGR system may also be a source of the oil, as well as the ventilation connections to the crankcase.

Tony H · #9 01-13-2017, 12:24 AM

You can add an additional oil separator-the mesh inside the valve cover doesn't take out much-the vapors are too hot to condense there. The crankcase vapors build up in the intake track and on the intake valves causing the soot we all see when you pull the heads.
Here's an example

LARGE VMS ALUMINUM OIL RESERVOIR CATCH CAN TANK W/ BREATHER FILTER BAFFLED BLACK | eBay