Oil in the Air Filter (and not from the vacuum pump)
 

I rebuilt the vacuum pump on my 1980 300D about a year ago, so the oil in my air cleaner isn't from that. The only other place it could be from is from the black hose that comes from the valve cover (I know it's from there). But why? I have ~140,000 miles on it, and the car starts and runs fine. Except that I have horrible fuel mileage (e.g.- ~14 mpg), and it consumes tons of oil.

I'm guessing that I have horrible fuel mileage and lots of oil consumption because it all goes into the air cleaner. Any time I put a new filter in, soon after it becomes soaked in black oil, so I guess I can't expect to have good mileage. Someone told me to try replacing the valve cover gasket and the hose from the valve cover to the air cleaner. Do you guys think that would cut it? Any other possible fixes/solutions, for not only this problem, but also related to excessive fuel and oil consumption?

some recent threads have been started on high oil loss. You should read these cause they address alot of your questions in them.

You have my problem.
My air filter gets oiled by blow-by.
The car runs great, uses little oil, yet I change the filter every 1500 miles.
One way to see is open the valve cover oil filler while she's running, if smoke puffs out, you've got blowby.
Quick way to tell how sound the motor, I'm told, if there is smoke it is an object of concern. (possibly low compression or valves)
That being said, I didn't know this when I bought the car, and I love my car, and it runs good. So I'm kinda glad I didn't look for that when I bought her.

What do the real MBZ mechanics think?

'80 300CD,
non-turbo, but GOES!

Long live the MBZ diesels!

oil in air cleaner housing
 

1. do a "search" on this site for "blow by" (excessive crank-
case pressure which may be forcing oil from top of engine
through hose to air cleaner chamber)
2. the other two symptoms you mention, in conjunction
with excessive crankcase pressure MAY point to ring/
cylinder wall wear.

How easily/quickly does it start on a cold morning ?
Does it smoke excessivley under acceleration ?

Compression check and a "leak down" test are
definitive tests

oil in air cleaner
 

it may also be valve stem seals.

I am no expert ,but one of the resident professional wrench
turners will chime in.

Everything else seems OK
 

It starts up perfect when it's cold, a second of cranking at normal temps., and probably just a couple of seconds when it's cold out (e.g.- 50's here in winter in Florida). It can also start witout glowing with normal temperatures outside, and not having been driven, so I don't know if it is something engine-damage related.

As far as exhaust, I only get a barely noticeable amount at start up, and I never see exhaust behind me when I'm driving. Whenever I've seen someone else drive the car off, there is no visible smoke. Although I'll admit, the exhaust does smell NOXIOUS. It doesn't smell "bad" (I've been behind some MB diesels that stunk) but it smells really, like polluting and I can't really explain it any other way, but poisonous/noxious, etc.

Physicists reported yesterday that the recent close passage of an asteroid to the earth has caused a serious problem in Mercedes diesels. The resultant change in gravitational fields is causing oil to be drawn into intake manifolds. Mercedes Benz will be releasing a technical bulletin on the matter next week.

One thing I just remembered is that every once in awhile the thin silver metal line that attaches to the bottom of the air cleaner would sometimes be disconnected, I guess from engine vibrations. Is that the oil return line? Could that have anything to do with it?

I got a sneak peak at that technical bulletin and it mentioned something about replacing the muffler bearings.:p

All joking aside:
I might suggest just disconnecting the hose running to the air cleaner that's coming from valve cover and re-routing the hose into another container to see how much oil it collects over a period of time.
The thing that confuses me is how something like blow-by could cause such terrible fuel economy.:confused:

What kind of oil do you use? I ask this because my car had never had a Diesel rated oil in it until I got it and it used quite a bit when I got it.... after 40k miles of Delo it uses less and less all the time. I don't usually even need to add oil now between changes even with a small leak.

Delo!
 

I've had the car about 3 years and 20,000 miles, and have used Delo since then.

Can I just disconnect that breather hose from the air cleaner, and then plug the nipple on the air cleaner? And put the end of the hose into a container like suggested?

Keep your oil level at the low mark on the dipstick. I think you will find that this reduces your consumption. Also, use a 15W-50 oil during summer.