OT mercedes 5 cylinder diesel

[Linus Tremaine]

So,
a 1979 mercedes 300sd has appeared in my life. It was free! It runs sweet, cruises nice, shifts nice, looks pretty good, starts stops and steers like a dream.

Bad? It smokes REALLY bad. Its embarrassing to drive! I think its unburned fuel- but I am worried that it might be oil. I would expect it to be more black if it was unburned fuel and it seems like its more blue/grey. Only had it about three hours.



Where do I start?

[superstator]

Diesel smoke, I've learned, doesn't tell you the same things gasoline smoke does. Blue/grey is usually unburned fuel thanks to bad timing or running cold (bad glowplugs, or just being slow to warm up). Black is soot, and again comes from bad timing, or from running hot or under extreme load. Oil getting past the rings can't really be diagnosed the same way it can in a gas engine - you just have to watch your consumption and look for other signs like blowby.

If it runs nicely otherwise, you might just need to tweak the timing a little - I think the blue/grey smoke usually means you're retarded, and black means you're advanced. Or is the other way around?

[4flattires]

The 300 was always a bit underpowered for that size sedan in my opinion. I had the smaller 300D for 400k miles until I was rear ended. Loved that car to death, never let me down and was solid as a rock. You'll have fun.

Jeff

[Blueboy]

the SD has a turbo vs just the D which was normally aspirated.

this is a total guess, yet, if the turbo is not functioning properly, you will get huge clouds of smoke as the engine is not burning all the fuel getting to it.

this sometimes happened to me in Brasil where I had a 110 with 300tdi.

if the revs were not high enough to get the turbo going, there were just clouds of black smoke and of course very little power.

didn't happen often, yet, sometimes starting from a dead stop in 1st with a heavy truck on an incline just wasn't enough to get the turbo boost up.

once the revs were high enough, everything was fine and you could feel that moment as well as see it on the tach.


Jaime

[Tim Smith]

Linus,
If you weren't on the other coast, I'd start telling you about all the pit falls of that car. ;) That would be a short post.

I had a 300TD with about the same mileage and I too was rear ended. Maybe that tells you something about the turbo lag? :p

If the motor was taken care of, you are probably just talking about timing issues and maybe some bad injectors. You could look at http://www.dieselgiant.com/ for some specific help around that. The fellow there seems quite knowledgeable and has a bunch of YouTube fix-it videos.

There is the possibility that you need rings. The easiest way to check that motor (without a compression test) is to let it run for a bit till warm, then loosen the oil fill cap. If the cap sits there with no puffing of smoke, then it's the best compression you could hope for. If it rattles around with maybe a little smoke, then you've got average to poor compression. If it pops about like a boiling tea kettle, then you need rings.

Those cars are a fill it and go tank. Not to say I'd prefer one over my current series but they are pretty good. Have fun!

[4flattires]

the SD has a turbo vs just the D which was normally aspirated.

Not wanting to turn this post into a full blown MB post, but the turbo vs non-turbo is a matter of the vehicle year, not D vs SD....and not just for the early years, it's true of the latter years as well.

Linus, since you might just be on the first tank of fuel the car came with, can you validate it is true #2 diesel with the PO?

Jeff

[Tim Smith]

...Linus, since you might just be on the first tank of fuel the car came with, can you validate it is true #2 diesel with the PO?...Good point. And if it was #2 then can you find out if it was bottom of their heating oil tank or not? :D

More to the point, a clogged fuel filter could lead to poor fuel flow at the IP. That could also be the source of smoke. Lean running diesels smoke too ya know.