I read about fast glow/ post glow plugs. I understand that post glow means that the glow plugs stay on for a little while after the engine starts. There are kits available for 4 and 5 cylinder engines, but somebody told me that 87 300D comes with factory installed fast glow/ post glow plugs. Is this true?

From what I can tell by reading the manual, the 1987 300D does not apply any power to the glow plugs after the car has been started.

There was a design modification on the later 603 diesels (I'm aware of the W124 ones anyway, like '88 and '89 years) that kept the glow plugs on after the engine starts (up to 17.5 seconds in 1988, and up to 60 seconds in 1989 & later).

My 87 300D tends to be cold-natured on startup. A bit of rough idle and unburned-diesel smoke. I think it bothered the previous owner quite a bit, and I can see how it could be embarassing in a subdivision neighborhood. Fortunately (well, in my opinion!) I live further out and I don't care if the car smokes some for the first minute. I did have one bad glow plug when I got the car, and replacing it helped the rough idle at startup some. I suspect the other five might be getting weak.

Are you asking your question because of these 87 300D startup characteristics?

Ken300D

Thank you for your reply.

Yes, when the engine is cold it starts right away but then starts to miss. I found out that cylinder 1 and 5 are not working. I checked the compression cold and hot. All cylinders were with in +- 10psi. I switched the injectors and the glow plugs but it did not make any difference. The only solution I found was to turn on the glow plugs manually for about 20 sec after the engine starts.

Could it be the fuel injection pump, but then why turning on the glow plugs makes it better.

Any suggestion's.

Good to have your experience on the results from replacing the injectors and glow plugs. Perhaps I'll leave mine alone then, as the glow plugs all test good now.

The car starts immediately and runs well. Then at just about the time when the glow plugs would be cooling down from "red hot" the idle gets a little rough. And the unburned diesel smoke starts. So, I run the engine speed up to about 1500 rpm and let it smooth out. It is interesting that some people say they don't have this idle/smoke issue. For me, I can live with it easily given all the other great things about the car.

I find it interesting that my '82 300D does none of this. It idles smoothly right upon startup, and little if any unburned diesel smoke.

How did you manage to manually turn on the glow plugs for 20 seconds after start? Did you trick the glow plug relay somehow or did you direct-wire all the glow plugs to the battery? Or something else?

The other thing that occurred to me: I wonder if the glow plug relay from a later 603 engine could be retrofitted into the 1987 300D? I am assuming that it is the glow plug relay itself that contains the "after glow" control logic. Frankly, I'm not sure its worth $150 or whatever the GP relay costs to make the change. But if the relay failed it might be better to use the later part.

Ken300D

I soldered one wire to the coil of the relay and another to the 11V supply inside the glow plug controller unit. Then I connected the wires to a toggle switch under the dashboard. So when I turn on the switch it energizes the relay and glow plugs come on.

I had a 77 300D before but never had this problem on that car.

The fast glow/ post glow plug kit is for 5 cylinder engines. It comes with the controller and four glow plugs. Cost is about $95. This kit can be used with an additional relay to energize the sixth glow plug.