Mercedes-Benz: 300SDL 87' Smoking / rough at startup

You've checked the usual suspect, the glow plugs. I hope you installed
either Bosch or Beru glowplugs, other brands can be "iffy". New isn't
always 100%.

Without knowing the engine's mileage or whether it was ever overheated
I'd suggest you first add some injector cleaner to the fuel. The smoke
is uncombusted fuel due to poor atomization. Has the fuel system - lines
and filters - been opened recently? If so, there could be an air leak at
a connection; air prevents full injection pressure and that causes poor
atomization.

Some years ago I replaced the rack damper pin on my 300SD but didn't get
its adjustment correct. Too tight and the engine started and ran like
yours, too loose and its hot, not cold, idle would sink so low that the
engine stalled. I don't know if your six also has a rack damper pin but
it's something to consider.

Finally, and hopefully this isn't true, one must not rule out a cracked
cylinder head, especially if the exhaust smoke is somewhat delayed and
white. These are fine engines but their aluminum heads are prone to
cracking if the engine is overheated. Look for coolant in the oil and
oil in the coolant and have the compression checked before proceeding
down this expensive repair path. Sorry to bring this up but it's a
possible cause of such symptoms.

The smoke is bluish on startup.

Is there any way to check whether the plugs are drawing enough
current? They were Bosch and 2 were dealer stock.

I don't see any signs of oil in coolant, or coolant in oil, but I have
considered this, as I know of this tendancy. I did find some oil on
one of the glow plugs threads, and I do consume a little oil, but the
car continues to smoke for about 5 minutes after start, unless I get
it on the road. Then smoking stops after a 1/2 mile or so. It also
gets worse with cold. My experience has been glow plug system in the
past.

The car has 206K on it. I'm going to check fittings for leakage.

I mentioned the stainless bellows that seems to link the exhaust
manifolds? It has a leak. Could this be a part of the problem?

What is a rack dampener pin? Where is it?

THanks,

Tim

"T.G. Lambach" <net> wrote in message news:<net>... 

In my last post I omitted to say that I had some rough starting after
installing new glow plugs due to, and I'm embarrassed to say, a loose
wire on a glow plug. The clue was that the glow plug lamp flashed after
the engine was running - as if to indicate a bad glow plug - but it was
just a bad mechanic!

The stainless steel expansion bellows on the exhaust connection to the
turbo is not an issue here.

Ignore the oil on the glow plug threads, it's not indicative of a
defect.

The rack damper pin on the old 5 cylinder 617 engines is on the aft end
of the injection pump. But I'd advise against making any changes to it -
if there is one on your six cylinder engine - for an additional variable
is added to the equation - which hasn't yet been solved.

Your added description of the extended smoking leads me to believe that
lube oil is being pulled into the engine through its valve guides whose
plastic valve stem seals may be worn out. Or, much worse, that the
cylinder head is cracked. Was this engine ever overheated?

An additional symptom of a cracked head or busted head gasket is rapid
and unexplained overheating. You don't mention either so let's assume
it's neither of these baddies. Short of opening the engine a compression
test is the definitive way to know.

Before proceeding with any heavy $$ or work, I suggest you pose this
problem to the Diesel NG on www.mbz.org Many of these fellows own or
have owned this engine and will give you more acute thoughts than I can
due to their hands on experience. It's free but one needs to sign up.

Meanwhile, I'll look in my HD for a couple of pix of cylinder heads
which I'll send you directly.

Tom