I have a problem with the glowplug system on my '95 300D too in as much as when starting, the glowplug light stays on for an age though if I start the engine after say 5 secs from cold, it fires perfectly. The light then goes out and doesn't return. Same when the engine is hot - lamp stays on but engine starts perfectly after a few seconds pre-heat.
I checked the glowplugs to earth and all have 1 ohm reading which I think is correct so, I checked the resistance on the water temperature sensor at the relay end of the cable.
At 68C, it was 325 ohms and at 20C, it was about 200.

I guess this indicates that the sensor is dodgy and needs replacement however, as this is reading lower than usual when the engine is cold, wouldn't that fool the relay into turning the glowplugs off more quickly and thus the light would go out too soon? How would this affect the afterglow??

It's my first diesel and loving the 'relaxed' and 'soothing' performance but this has me a little baffled and I don't want to take the inlet manifold to bits, replace the sensor only to find the same problem....!!

Any ideas guys???

Thanks


Paul