Originally Posted by 240Joe

A 240D running nearly constantly at 80 to 85 mph will use about 1 quart in 600 to 1000 miles. If you don't believe me, look it up.

Say you drive 12kmiles a year or 1kmile a month, and add a quart a month...and the engine holds 8 quarts. Say that soot is added to the oil at about 0.15% per 1000 miles...which has been confirmed by many oil samples.

It can be shown with a little math (and I'll leave that for an exercise) that the concentration of soot can never get higher than .15/.125 or 1.2%.

If soot is added at .2% per 1000 miles, which is very high, then you'll never get above .2/.125 or 1.6%.

A good synthetic diesel grade oil can easily handle 5% soot...and some 10%.

And now you can do the math for other combinations....say adding oil only once every 2 months or 2kmiles. Even with the .2% soot added every 1kmiles, you can't get over 3.2% soot....ever.

So, to sum up....if you have to add at least a little oil to the engine, and you change the filter once a year (this analysis excludes the oil you lose when you pull the filter out...but it would only make the numbers better), you can probably drive it forever.

Fire away.

240Joe