Just when it's starting to get cold too. Damn.

Anyway, I was leaving work 2 days ago, and when I went to start my 1983 300SD the glow plug light didn't come on. I had just been in the car about an hour ago so it was still somewhat warm, it started right up with no problem. I just figured the bulb had gone bad.

The next morning it was hell trying to get the thing to start. I have a block heater, but that doesn't really help me when I'm leaving work at night.

Usually I'd have my uncle help me with this, as he is a diesel genius, but he is out of town.

So, what do I need to do to find my problem. I understand it could be a bad plug or it could be the relay. I have another 83 300SD that I could pull the relay from if I know where it is.

Could someone post a picture of where it is located.

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1983 300SD W126 w/276k miles

It won't be a single glow plug bad that prevents you from starting the car. The car will start on 4 cylinders no problem and the 5th will catch soon after.

But when that bad glow plug failed it may have burnt out the glow plug fuse in the relay.

Fortunately, this is very easy to check. A picture is better, but until one comes along I will tell you where to look. The glow plug relay on your car is a small rectangular box about 1.5 x 4 inches, attached to the fender in the engine compartment just behind the driver's headlight assembly.

It has a cover on top that pops loose and lifts off. Then you can see the connectors and fuse. The fuse is nothing but a strip of metal between two bolts.

Besides the fuse, it is also possible the relay contacts have failed. But the first thing to look over is the fuse.

If you go on EBay and search on "Mercedes glow relay" you can find a picture of what the unit looks like.

Should be relatively easy to get going again and you need the glow plugs big time for cold weather.

Ken300D

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1982 300D at 351K miles
1984 300SD at 217K miles
1987 300D at 370K miles

No light for glow plugs usually means you have glow plugs that are burned out. You should check several things.
1. You need to test all your plugs with a ohm meter. Test them for resistance. If you get much resistance on one put in a new one.
2. You also need to check that the relay is getting juice from the battery.
3. Check the strip fuse in the relay. Make sure it has no cracks. Check the resistance on it too.
4. Check all the wires going to each glowplug fro resistance, to make sure they are all getting juice.

That hopefully will solve the issue.

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If it were me, I'd just replace them all and save the good ones for spares. The most sure fire method of checking is pull them and put 12 volts to them, they should glow red almost instently. I've had ones pass the ohm test and still be N/G.

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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"

They are available at the local Auto Zone. Pretty much Auto Zone only, the other 5 places in my town did not have them. Bosch, part number 80006. I believe it is a 12mm nut on the end of the glow plug that attaches the wire. Make sure the wire does not touch the block. It will provide a path straight to ground and will blow the 80 amp fuse in about 2 seconds. Smells bad too.

Replace all 5 and enjoy your new starting experience!

-Jim

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1995 S350D, Green with black leather interior.
Bought January 2008 w/ 233,xxx miles.
I did 22,000 miles during the first year of ownership.