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

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

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

Tom,

Thanks for your more than generous devotion of time to this.

I will check out the link.

Tim