240D and 300SDL....Do glow plugs stay on after engine start?

[airfoill]

Hi everyone,

I have an '82 240D and an '87 300SDL and I know that both these cars have glow plug relays that keeps time on how long that plugs stay on before start. However, does anybody know what happens when you start the car before the glow plugs go through their warm up cycle? Do they shut off after starting or do they continue through their normal cycle despite the engine already started?

Thanks

Herb
'82 240D
'87 300SDL

[Ken300D]

As far as I know, on these model years the glow plug current supply turns off when you release the key from the starting position (back to ON).

On some later diesel models, 1990-93, the glow plugs stay on for some period of time after startup. The length of time they stay on after startup is determined by the ambient temperature. At first they went with something like "up to 17.5 seconds" and later extended that to "up to 60 seconds". I don't know what MB did on the 1995+ model years. (Info from the MB W124 service manual.)

My 1987 300D smokes unburnt fuel for about a minute after startup. I think the smoke is the reason the previous owner sold it - he was scared the engine was trashed.

Ken300D

[mplafleur]

The book for my '87 states that the plugs may remain on for some time after startup to help reduce emissions.

[Ken300D]

Which book are you looking at? If it is the service manual, can you tell me which job number it is? If it is the CDROM, the file name is the job number.

I found the part about the glow plugs staying on after startup, and then further found that this applies only to the later years of the W124 diesels, not the 1987.

But it could be I read it wrong or the manual contradicts itself somewhere. My reference is Job 15-0705 in the 602_603 engine section of the CDROM.

Of course the direct method of telling what is going on is to use a voltmeter or 12v light bulb connected to a glow plug. Direct observation beats a service manual every time.

Ken300D

[mplafleur]

I don't have a MB manual yet for the diesel. The book I referred to was the Haynes manual I bought online from England.