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300 SEL 6.3 SMOKE!

3K views 10 replies 8 participants last post by  pd58 
#1 ·
I recently inherited a '71 300 SEL 6.3. The car is mostly in nice shape with most of the interior redone. Apparently the air suspension and engine were redone not that long ago. I think I am looking to fix it/get it fixed and maybe sell it.

It starts and runs OK, but I have never seen a car smoke like this (I've been a mechanic for 12+ years; I ran the car for 5 minutes and my whole neighborhood was engulfed in smoke). Smoke looks & smells like oil and there's oil residue in tailpipe. I pulled the plugs & all looked the same - heavy carbon & wet. Compression test shows all cylinders pretty much equal so I don't think it's a burnt piston or bad rings. Could it be fuel injection problem?

Thanks.
 
#2 ·
Does the car have a vacuum pump? I had a 73 280 with the 110 engine that developed a bad smoking problem when its vacuum pump needed a rebuild. Pump was identical to those used on the Benz diesels. Soon as the pump was making vacuum again, all the smoke went away.
 
#3 ·
Chances are it is a small and cheap fix..... I suspect that the rubber diaphram in the transmission vacuum modulator valve has gone bad... If that is the case that would cause oil residue in the tail pipe and bad smoke since now you are sucking tranny oil into the intake manifold and straight into your exhaust manifold.
 
#4 ·
Thanks. Will look into it next. Any idea where I can get parts for this thing? I'm new to M-B, I own a '71 Chevelle SS and my daily drivers are VWs (they're easy to work on), so I'm a little afraid of working on the 6.3 as I have read on quite a few forums that everything is so finicky.

Also, where to get a manual? I was given a version of WIS on CD (it's 5 CDs, circa 2003) but not sure I want to install it as it's a bit antiquated and looks like it wants to take over your computer.
 
#9 ·
You know this sounds crazy, but I put castrol 10-30 GTX in mine and it started smoking.
A local MB mechanic told me to drain it and put in the cheapest oil you could fine, he recommended Oreillys Brand 15-40 with soot control and it stopped. Just thought I would tell you because whenever I have obtained a new car I always want to put fresh oil in it.
Don't ask me why I picked castrol GTX, never again. Good luck.
 
#10 ·
Sorry it took so long to get back to this. Thanks for the great advice alabbasi; International M100 Group is where I need to be. I got it running, and I DO NOT WANT TO SELL THIS CAR NOW!

I now own an awesome piece of History! Now if i can just get the MFI tuned properly...
 
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