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 ?

Bob Little

Your car has the same engine that's in my SD and it depends on how well the engine was "broken in" when she was new. Also you don't say how many miles your car has or what weight oil you are using. Generally the diesel owners here on this board use a diesel grade oil 15W-40 or even thicker, 20W-50. Also believe it or not according to the factory manual, there is an allowable oil consumtion for these engines. It says 262 miles per quart. I know this sounds insane, but it is listed in the manual. If you are using that much oil, I would stay away from synthetic oil, it will cost you fortune.

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1999 MB SL500 (110,000 mi)
2004 Volvo V70 2.5T (220,000 mi)
2014 Tesla Model S 85 (136,000 mi)
MBCA member

You don't say the miles or the type of use the car gets. I have had diesels that burn oil when just idled around but go to very little consumption when they where worked for a extended period of time. Take it for a trip and run it hard. High heat and pressures may take the glaze off the cylinder walls and seat the rings a little better. Just a thought.

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Mark
82 300SD 110k
91 Caprice SS
92 Jetta TD
97 Cadillac Concours(300hp)
84 Celebrity 4.3L diesel

Rick and Mark, the car has 125k on it according to odometer. It burns the same approximate amount of oil with Pennzoil 20w50 which is what I used up until recently as it does with Delvac I synthetic diesel oil which I am put in at last oil change. Obviously, I can't continue to pour synthetic in every week so I will be switching to Chevron Delo 400 soon. (A friend told me Delo 400 lowered his consumption significantly.) I figured that that running synthetic for a while would at least help clean the engine. I have given the car numerous "Italian tune-ups" and tried to blow out any carbon, etc. It runs smoother now but consumption still same. I thoroughly enjoy the car but am amazed that it can burn that much oil with so little smoke, no
wetness in the tailpipe, etc. (Mark, I looked on my cd manual but haven't found anything about permissable oil consumption. Can you tell where you found those figures in the manual ?) Thanks for the feedback.

Bob.

An Italian tune up will not really gain much. What you describe sounds to me like a poor break in or excessive idling at some point. What you need is an extended run at high power settings. With lots of heat and pressures the glaze on the cylinders can be partially burned away and the oil rings seated. This can take hours of continuous running. The only other option is to take a hone to the cylinders and remove the glaze that way.

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Mark
82 300SD 110k
91 Caprice SS
92 Jetta TD
97 Cadillac Concours(300hp)
84 Celebrity 4.3L diesel

Bob,

Sorry, I cannot help you with your problems. But, I wonder if you are getting good mpg since you are fueling the engine with a qt of oil every 250 mile.

David

Mark, you may be on the right track about the cylinder glazing. Hope that is it because I love driving this car. I have made numerous relatively high speed short trips (10 to 40 miles) but nothing longer. Thanks for the input.

As for gas mileage, last time I checked it was about 24 mpg combined.

Bob,

Thank you for the reply. When you have a chance to use Chevron Delo 400, please let us know the result.

David