That is true. But on a '83 240D, it has nothing to do with starting the engine.

If the glow lamp is not illuminating at all, the issue is not temperature. The problem is that one or more of the glow plugs are inoperative. Or the lamp is burned out. Or the timer unit is malfunctioning.

If you glow the plugs and do not attempt a start, how long does the relay remain closed? You should be able to hear it "clunk" when it opens.

True but it has a lot to do with how long the gp stay on to heat the cylinders....starter, glow plugs and a good battery has all to do with starting...

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I think the only sensor in the later head is for a temp gauge, the early head had one for the GP relay & temp sensor.

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1985 Euro 240D 5 spd 140K
1979 240D 5 spd, 40K on engine rebuild
1994 Dodge/Cummins, 5 spd, 121K
1964 Allice Chalmers D15 tractor
2014 Kubota L3800 tractor
1964 VW bug

"Lifes too short to drive a boring car"

Maybe its built into the relay then...I remember on my 82....when the engine was cold the gp light would stay on for a bit when the engine was cold....once hot it would stay on for about a second....then go off....so something has to be telling the rely the temp of the engine....

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Unfortunately, the circuitry needed to support that theory does not exist. The temperature being measured is that of the engine compartment, not the engine itself.

I have to agree that GP is the most likely culprit but as charmalu said, try pumping the primer a couple times and see if there is any improvement - you may have a slow leak that causes temp fuel starvation. Maybe both.

A 240D should kick right over if all is set well. Just a 1 or 2 sec bump and she's running.

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Codifex
1981 240D ChinaBlue (Got her running with a donor engine.)
1983 300DTurbo w/sunroof.
1984 300TD manual sunroof. (Electrical Gremlins)

A hot wire from the battery and quickly touched to the top of the GP will tell the story..no spark= No good. (not for the "looper" type) Thats a quick check if your on the road or dont have your tool box. I have never set a car on fire by doing this or has the old mechanic that showed me this quick check.
The best check is to pull them out (I pull the hard injector lines also) and use that hot wire and a ground wire and see if they quickly get red hot.

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1985 Euro 240D 5 spd 140K
1979 240D 5 spd, 40K on engine rebuild
1994 Dodge/Cummins, 5 spd, 121K
1964 Allice Chalmers D15 tractor
2014 Kubota L3800 tractor
1964 VW bug

"Lifes too short to drive a boring car"