So my 300SD runs very well, except recently I've noticed some smoke at starup, which hasn't been an issue before. It's a grayish smoke and it only happens when the engine is cold. I've also noticed sometimes when accelerating on the freeway there is a little smoke, as well.

The valves were done less than 4k ago and it doesn't seem to burn oil, as I don't have to top it off ever between changes. The engine has 101k on it.

I'm thinking of replacing the glow plugs to start with, but that would only help the startup issue, and not the freeway deal.

I am running B99, which I've read can carbonize the injectors and lead to smoking, but I've only been using B99 for about a month.

Any thoughts?

My 79 300D smokes at startup as well. If I spend many miles at city speeds then punch it to get to highway speeds it will always smoke. I think this is normal. New glow plugs didnt change the smoke at start up in my 300sd. My 85 300D, even though it has the same glow plugs has never smoked at startup for more than a second or two. I wonder if the later 617s glow longer?

__________________
1959 Gravely LI, 1963 Gravely L8, 1973 Gravely C12
1982 380SL
1978 450 SEL 6.9 euro restoration at 63% and climbing
1987 300 D
2005 CDI European Delivery
2006 CDI Handed down to daughter
2007 GL CDI. Wifes

I have noticed that, at the very least, it starts up more quickly if I run the glow plug proceedure more than once before engaging the starter. I take that as a sign that maybe the plugs should be replaced.

I'll probably do a quick valve job, as well.

If it's black smoke on the freeway like under load going uphill then I'd suspect carbon fouled combustion chambers. Blow em out using fuel additives and running the car top speed. Valve adjusts wont alter smoke, more like injector pump timing unheard of bein needed at 101k miles though.

I've noticed that if I run the glow plug proceedre more than once the start-up smoke issue is gone; so I'm thinking they're not getting hot enough and a replacement is necessary.

But as for the freeway driving, how much smoke is "normal" for a diesel?

Thanks for the help.

If you are going up a steep hill or are under hard acceleration after going city speeds for some time that is normal. It shouldn't be black or really dark. You could try sea foam or diesel purge, or just do an Italian tune up.

As far as the glow plugs go, if the car starts right away they are probably fine. When I had one bad plug I had to hold it to the floor and crank for 30-40 seconds to start it.

__________________
1959 Gravely LI, 1963 Gravely L8, 1973 Gravely C12
1982 380SL
1978 450 SEL 6.9 euro restoration at 63% and climbing
1987 300 D
2005 CDI European Delivery
2006 CDI Handed down to daughter
2007 GL CDI. Wifes

Sounds like fuel. I bet you have one bad glow plug. Does it miss a bit?

Tom W

__________________
[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

Just recently I've noticed what might be a slight ping at idle, but it's only occasional and I can't be sure if it's a ping or if something is just loose in the engine compartment.

The only other thing I'm concerned about is the fact that I switched to using B99 last a little over a month ago.

Most of the time it starts up very quickly (w/in two to three seconds); but it starts up immediately (w/in one to two seconds) if I run the glow plug sequence more than once before engaging the starter.