I have a 1987 300D Turbo and was unable to start it this morning. The temperature is 0 F. In the past, I did not have any trouble starting the car in -10F weather. This morning, the glow plug light did not light when I turned the key to the right. I just heard a clicking coming from the dash. I could not even start the car when I pulled into heated, indoor parking and received a jump start. Does this sound like a glow plug problem or is this a problem with the Preglow Time Relay?

Hello, and welcome to the forum.

Normally, for diesel related questions, the "Diesel forum" would be the place to post your question.

Diesels that fail to start are a hot topic right about now. I'll provide answers here for you:

You are correct in that the problem lies in the glow plug circuit. The problem may be one or two failed plugs, or the problem may be in the glow plug relay itself.

If you are somewhat handy with a voltmeter/ohmmeter, you can perform the following tests:

1) See if you have 12V going to any one plug when you turn the key to the preglow position. You must get setup to do this prior to turning the key because you only have 40 seconds or so. The plugs are a bit difficult to get to on the 603, so select the easiest one to attach a small test lead. If you do not have 12V at the plugs, report back for further advice.

2) If you do have 12V at any one plug, you then need to disconnect the cable at the side of the glow plug relay and perform a test to see which
plug(s) are NG. The glow plug relay is a black box that is on the forward side of the driver's fenderwell. There is a cover that will slide off the top of the box. The box is about 2" x 3 1/2" x 5" long. There is a large plug on one side of the box.

3) Pull the cable with plug out of the relay and you will see six socket connectors in the plug. Set up an ohmmeter that can read very low values. It must be able to read 10 ohms full scale. Connect one end to one of the socket connectors in the plug and connect the other end to a good ground. The reading must be at 1 ohm or below. Repeat this test for all six glow plugs.

You will probably find one or two that read infinity. The plug is open and provides no glow.

Replace any plugs that are above 1 ohm.

Report back on your progress.

Good luck.

As Brian said, do some testing.

The glow plugs should be drawing 10 amperes or so each. If only two are out, you probably won't get a glow light, but the 40 amperes will dim lights. Leave the door open and observe the courtesy light, for instance. If there is no dim at all, you might have a lot of bad plugs, a bad 80 ampere glow plug fuse, or a bad relay.

The clicking under the dash was probably ACC control unit relays, responding to cold temperature by closing outside air vacuum switch and turning blower motor off until engine temperature reaches minimum.

Come on over to Diesel Discussion forum, lots of us there.

Best Regards,
Jim

I wouldn't rule out a bad battery. I'd test it before pursuing other problems.

__________________
1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13