In my '83 300D,(257k miles) which has been running flawlessly up until yesterday morning, it seems my glow plugs are not glowing enough. I've measured the resistance between the glow plug and the block (with the electrical lead attached) and each plug is about 0.5 ohms. The glow plug indicator light on the dash stopped coming on when this problem arose but I can hear the relay clicking behind the driver's side headlight.

I measured voltage and found about 10V at each glow plug for about 25 seconds or so with a cold, but not cold soaked (overnight) engine. I seriously doubt all of my glow plugs failed simultaneously. In the morning, I can get the engine to start by cranking the hell out of it.

The engine starts normally (<1sec cranking) if not more than one hour has elapsed from the previous run and I wait for what would normally be the preglow time with the key in the preglow position. Ambient temperature about 35degrees F.

Then engine starts with more difficulty (2-3 seconds of cranking) than usual after about 3 hours have elapsed. Ambient temperature about 35degrees F.

The engine is difficult to start after sitting overnight in 25degree weather (30 seconds of continuous cranking), and emits a large cloud of dense grey smoke as it begins to catch.

The fuse under the cover of the glow plug relay is okay. When I first checked it, one of the screws holding it in place was almost completely loose. The connectors in this area were all clean and free of corrosion.

I'm starting to think that my glow plug timer relay is limiting current to the plugs, thereby making the car difficult to start when cold. Remember, the indicator light in the dashboard has stopped coming on when this problem arose. Is this thing rebuildable or otherwise serviceable? Do they normally fail without warning as this one seems to have done? All help is greatly appreciated.

Thanks in advance.

James