I have a great driving 1985 300SD. It has only one serious flaw: it gets about 250 miles per quart of oil. It smokes very little - just a little black smoke on hard acceleration. My mechanic and I have replaced or checked everything we can think of, i.e., new timing chain and valve seals, fixed 2 small leaks and car now does not visibly leak at all, checked turbo for leak, etc., etc. The car runs smoothly and has good power for a diesel. The compression has been checked and the readings are all between 380 and 400 except for number 2 which is 350 (still not very low). I don't understand how an engine can have decent compression, very little smoke, and yet burn this much oil. Has anyone seen this before ?

Thanks for responding, Bill. You make a good point since most of my driving is back and forth to work on I-64. I might drive my other car to work a few days and let my wife tool the SD around town to see what consumption is under those conditions.

I had hoped the problem might be a sticking oil control ring so I have been running Delvac I synthetic since last oil change in hopes of freeing up the rings. No change yet though and of course I can't keep pouring synthetic in it due to $$. I ran Pennzoil 20w50 before the switch and oil use has not changed.
A friend told me that Delo 400 diesel oil cut his consumption so I may try that next.

Very interesting ! That's two recommendations I have now for Delo 400. Still, I plan to run a few more quarts of Delvac I through before making the switch, just to clean the engine well internally. I have no leaks with the Delvac I (already fixed them all).

I have used Mobil 1 in my 1978 280CE for about three years and love it. It seems the car runs better all the time. It definitely turns over easier in very cold weather.

240Ds are just marvelous old cars!

I'm not sure if this is applicable with diesel Benz's, however I read about it happening with VW TDis and experienced it myself. At higher RPMs, the intake suction actually draws oil thru the PCV. In fact, I've heard that in extreme cases (semis) so much oil is burned that it causes the vehicle to accelerate, thus drawing in more oil... until all the oil is burned up.
Please correct me if I'm completely wrong, here.

I have had the vacuum pump diaphragm fail and start to pump oil through the engine at an alarming rate (and 250miles to a quart is getting near the point of alarm) but it was readily apparent that something was amiss. When I stopped the car would be enveloped in a thick cloud of white smoke, and it made some extra knocking noises.

From what you say, there is a genuine mystery. I get 900 to 1500 miles to a quart in my 240D and a good bit if that leaks past the rear seal. But the smoke is noticable at idle and under heavy loads, like going up hill at highway speeds. To be unable to find evidence of nearly 6 times that much oil is unusual.

Has the car always used oil at that rate, or has it suddenly started or did it get to this point slowly? It sure seems like something is letting a significant quantity of oil go somewhere it is not intended and after a few quarts there should be some visible evidence.

I remember once adding oil to the injection pump on my 1975 240D, and being unaware of the overflow tube. fter adding two quarts I found my shoes covered in oil and my buddy's driveway soaked in it (it was Mobil 1 5W30 back in the old days and it was an expensive lesson). I was wondering where all this oil could go, but once again, when the oil went where is was not intended to be, it let me know about it pretty dramatically.

Jim

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Own:
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles

Owned:
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)

Hi, I know this is slightly off the topic, but someone in this thread mentioned 20W50 oil. Is that what I should be using? Right now I have 10W40 in my 300D-T. Is the 20W50 just an oil consumption cure? My car burns no oil in between 4000 mile oil changes. Thanks

Alex

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1983 300D (parked for four years)
2012 VW Sportwagen TDI Manual
2001 Miata SE
1962 Chevrolet Corvair Rampside

The vacuum pump diaphragm is something I do not know much about and my mechanic, who is an experienced mercedes guy, did
not mention it. That could be a possibility but from what I have read elsewhere I think the car would smoke significantly in that case. Maybe not. I was originally inclined to think the turbo was leaking but it apparently is not as my mechanic removed the cover and inspected it.

The car has used oil at about this rate during the year and one half I have owned it, although I wasn't actually measuring consumption it early on because I knew it had a oil cooler hose leaking and strongly suspected it needed valve seals because of white smoke on cold startup which went away in a couple of minutes. Once I replaced the cooler hose and had valve seals installed, it no smoked on cold start and has not leaked a drop in my driveway. I even cleaned the engine and checked for less obvious leaks but found none. I bought the car from the second owner who had owned the car for about 4 years and had very few records. I was so certain the car was solid mechanically I did not worry about that. I have never tried to contact the original owner but I may try to do that this week if I can track him down just to see what he says about oil usage.

Consider the valve stem seals ....

Also, black smoke on acceleration is fuel, not oil. Oil would be whitish blue, I think.

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George Stephenson
1991 350 SDL (200K and she ain't bent, yet)
former 2002 E320 4Matic Wagon - good car
former 1985 300 CD - great car
former 1981 300 TD - good car
former 1972 280 SEL - not so good car
a couple of those diesel Rabbits ...40-45 mpg

Bill, I have tried just leaving the oil 1 quart low - which is about halfway between the min and max marks - but this does not help.
I know on some mercedes people say this does make a difference but not on this one.