w124 300D coil light coming on...

[bigyin1]

Morning

Over the last 2-3 weeks my coil light has been coming on every now and again. It normally coincides with a slight rise in the engine temperature as the needles normally sits in the middle of the top "o" of the 80 degrees and when it moves to the top of the "o" the light comes on.

I can make it happen if I'm pushing on a bit and using the revs then when i go back to cruising the temp drops a wee bit and the light goes off. BUT this morning it came on/went off of its own accord when just cruising at 60.

When i had those fuel problems last month, i was told that there is an oil leak, possibly from the oil cooler, could this be causing the problem? Are they related? I don't have any problems starting so perhaps the coil light is a generic error that points to "something" wrong?

Any help very much appreciated as i'm going to Edinburgh in 2 months so need it to be 100% OK.

Cheers.

 

[bolide]

The light is controlled by the glowplug relay. The function of turning on after the engine has started is used to flag up a failed glowplug. When it does this the glowplug light stays off during the startup glow phase and then comes on after the car starts. That's a good indication of one or more failed glowplugs

The lamp coming on at any other time would suggest to me a bad relay or perhaps a bad connection to it. The glow plugs are easy to test - just pull the 6-pin plug off the glowplug relay (the black box on the n/s inner wing) and measure the resistance of each pin to a good earth point on the block. They should measure 0.7-0.9 Ohm but it'll be very dependent on temperature and the accuracy of the meter you use

If any of the glowplugs is out of spec I'd replace them. If they're all around 0.7 Ohm I'd look at the relay

Nick Froome
www.w124.co.uk

 

[mhuk]

Hi,

Sorry to bring an old post up.

My 1990 w124 300td is bring the coil light on when running. I think the glow plugs might be duff. Runs a bit funny. How do I change them? Is it a manifold off job?

Regards

 

[SilverSaloon]

follow this guide to use the relay and a multimeter to test what glowplug needs replacing:

Mercedes Diesel Glow Plug Repair

The only reason to remove the manifold is if its in the way of removing the glowplug - so if you can get to it then no need to remove.... i think they are easier to do on the earlier w124 diesels. you may get away with removing just a bit to get access to the plug you need to replace.