How Smoke is too much?? - PeachParts Mercedes-Benz Forum

#1 05-14-2002, 09:20 AM

I have recently came in to the possesion of a pair of 240Ds, a 74 and a 75. The 74 is a prodject for later since it needs alot of restoring. My 75 starts and runs great, but smokes. Smoke is a little heave at start then thins out after a minute or two. It allways smokes some, never black smoke, not even on accel.
The smoke is a blue-ish white, like oil. Im a technician but all my diesel work has been on Dodge trucks and one Diesel Rabbit.
Oh, the 75 sat up for 2 years before I got it. Any Ideals on whats up? Pump timing? Rings? Valve seals?
Thanks for any help!!
:p

can-do · #2 05-14-2002, 09:55 AM

Greetings Coffee,

If the car has been sitting for any length of time, it could simply be stuck oil rings on one or more pistons. The best thing to do at this point is drive the car a little harder, higher speeds for periods of time to see if that doesn't loosen them up. Should see some type of results after a week or so. It also wouldn't hurt the engine if you haven't done it already to change all fuel filters and run some diesel purge through the system. After a few weeks I'd do a compression test as well as a leak down if your smokey problem doesn't subside. Seeing as valve seals are a pretty easy repair, that is one item I'd look into doing. You didn't mention the mileage on this beauty, but after a period of time, the engines grow tired and their diet starts to include oil due to generally worn rings or out of round cylinder sleeves.

Charles

JimSmith · #3 05-14-2002, 11:19 AM

Coffee,

I had a 1975 240D with a tireless engine that just dissolved in the winter salt of the Northeast. But it did smoke and there were a few items to check.

First, if the smoke is mostly at idle, I would suspect the valve seals and the vacuum pump diaphragm. I would also check the oil bath aircleaner and make sure it is not plugged with mud. A plugged aircleaner will make the other conditions worse, and smoke more, especially at start up.

There is a translucent white tube that runs from the vacuum pump to the air intake manifold or the air cleaner, I cannot remember exactly. If the pump diaphragm is leaking, your car actually has a butterfly like valve in the intake that restricts airflow at idle, and creates a mild vacuum in the intake system. Any leakage past the pump diaphragm gets sucked into the intake and you get smoke. I had this thing fail "catastrophically" on the 220D and at idle it was spectacular. At speed it hardly smoked.

The intake valve seals will leak and cause similar problems. At the age of your car, I would think the seals were shot even if the car was under 100K miles. If it is a higher mileage car you should consider pulling the head and rebuilding it.

I ran Mobil 1 in mine way back then, and it seemed to help with smoking and really helped with starting when I was in Alaska with the car. In the old days, Mobil 1 came in one viscosity range. Today it is available in much greater variety, and in Diesel specific versions (Delvac 1, which I run in my 1982 240D and 1998 E300D TurboDiesel). One of these may help clean out any accumulated deposits (Delvac 1 would be my recommendation) and get the rings and other parts seating correctly again.

Good luck, Jim

#4 05-14-2002, 02:15 PM

Im not sure of the mileage...... only shows 43000, but does not have 100000 place on odometer..... so it got some where between 43000 and 1043000

Thanks..... I'll check Vac Diaphram.... power brakes not as good as they should be.... so may have a vac problem...