1984 Mercedes Diesel - What's up with this thing?
 

There is a 1984 Mercedes 300SD at one of the places I find weird cars. It got towed into them, it had been traded in at a Mercedes dealer a few weeks ago. Since it was towed in, no one bothered to see if it ran. Well, I got it started. It will run, the turbo spools up when you rev it, but it smokes black under the hood. The air filter housing is covered in soot, and the smoke looks like its coming from the filter housing, or the turbo under it, but there is so much soot and smoke that I can't see where its coming out of lol. I can't test drive it, but it did move back and forth so it has at least reverse and 1st gear. None of the gauges move at all either. The odo shows 263,000 KMs (163k miles) but since the gauges aren't working I have no way to know how correct that is.

Is there a common cause for this sort of thing on one of these cars? The smoke out of the tailpipe wasn't bad at all, just a little black, no blue. I am only asking because it will be CHEAP, but at the same time if it's a big repair I don't even want to bother grabbing it.

On those old mercedes diesels adjusting the valves is very important...If they are bad enough it could be loosing compression causing the fuel not to burn well. Also on that motor there is a pump that times the injection of fuel to the cylinders. If it isn't timed correctly it will smoke like a volcano.

Ok, but the smoke isn't coming out of the tailpipe, it's actually billowing out under the hood. Would the injector pump being out of time do that? It's really weird, maybe there is a crack in the turbo housing or something?

It's more common for the manifold or flex pipe to crack.... I've never seen one with billowing smoke under the hood though... Maybe the down pipe completely rotted away? Is it really loud?

You need to remove the filter housing to take a peek around. You can't see much with it in the way.

It's not really loud, and there is still exhaust coming out of the tailpipe so there is still some sort of exhaust system left on it. I think I will have to wait until there is no one around there tomorrow and start pulling some bits off so I can see what's up better. They sort of frown upon that but if I go at lunch time I should have a good 45 minutes without anyone seeing me lol

No smoke out of tailpipe but only under hood sounds like it's burning oil from a leak off of the turbo or exhaust.

The turbo has an O-Ring into the intake manifold, and the turbine outlet has a clamp. It sounds as if someone tried to remove the turbo, and messed up the O-Ring. The black smoke is caused by loss of boost. It is coming out under the hood, due to a loose clamp or blown gasket on the turbine side.

HTH Bart

Thank you. It's not burning oil smoke, it is soot/diesel smoke. I will take the air filter housing off it tomorrow and check out where the turbo o-ring and clamps are.

The O-Ring is inside the turbo compressor discharge housing where it connects to the intake manifold. The clamps that I mentioned connect the exhaust pipe to the turbine outlet. There is also a copper gasket between the turbine inlet and the exhaust manifold. If the nuts are loose on the exhaust>turbo flange that may be where the smoke is leaking.

I understood it to be fuel smoke:thumbup: I have an old Dodge with a 4.0 Mitsubishi diesel.:turtle: It now has a turbo from a 300D Mercedes:D

Thank you again for the info. I knew that you knew what was going on with the smoke, I just put that in for the person that replied about it being oil burning on the exhaust. From the sounds of it the soot/smoke is going to be turbo housing related, especially since it is right below the soot covered air filter housing. I have never had one of these cars, and it is not in a place where I can take my time to decide if I want it or not, so I need to do some gorilla diagnosis before I buy it lol.

There is a flexible connection from the turbo to the exhaust pipe that is most likely broken. Unless you have a cracked exhaust manifold, less likely.

See if you can remove the air filter housing and run it. I pretty much guarantee it is a cracked/broken exhaust bellows/pipe. However, black smoke will not happen with a boost leak unless the engine is under load, so if it is smoking black at idle, there is something more seriously wrong with it than a simple leak.

is 1984 old enuf for it to not have a sealed crank case?

i know in Isuzu's 1983 was the last year for there diesels to have a open crank case vent. 84 on its routed to the air intake.

excessive blow by seems to be one possabilty to me, if all the smoke is coming from the crank case vent.

One other thing that will cause black smoke is plugged fuel filters. There is supposed to be a minimum of 24 psi at the injector pump inlet. There are two filters, one at the lift pump inlet and one between the lift pump and the injector pump.

Bah, there was people around it when I went there today so I couldn't pull any parts off to have a look. I'll try again tomorrow. On the plus side I did see a Mercedes 240D with a manual transmission when I was there. I yacked with the owner about it, he just keeps it around for a beater. Man now I want that thing way more than the 300SD lol

Heck if you can afford to just buy them BOTH:D and fix them later.