I have an 87 300D with the 603 engine that uses about 1/4 quart per 5000 miles. The engine has at least 187,000 miles. More likely 235,000 miles.

I purchased a 95 S350D 3-4 weeks ago. It has 230,000 miles on it. I've put about 2,000 miles on it and have used about 1/8 of a quart.

I'm watching and preparing for an "eventual" engine issue.

Lampbum2 your 350SDL went from 1/2 quart per 5000 miles to 1 quart per 3000 miles in 78,000 miles.

To compare apples to apples you went from 1/2 quart per 5000 miles to 1.67 quarts per 5000 miles over the period of 78,000 miles of driving.

Based on that I could have 78,000 miles or so left in mine. (I could have a little less or a lot more. Hopefully a lot more.)

-Jim

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1995 S350D, Green with black leather interior.
Bought January 2008 w/ 233,xxx miles.
I did 22,000 miles during the first year of ownership.