I am having trouble getting my '81 300D(non-turbo) to start lately. It is VERY cold in the Texas Panhandle(9-14F).

My glow plug light and relay work fine. The light goes off just like normal and the relay kicks off at the same time as usual.

My question is whether or not it's possible for there to be a glow plug problem with the light still working the same.

The engine has been running very roughly lately so I do suspect that I have some injector issues as well. I also have noticed that it starts easily if the engine is warm but practically kills the battery/starter if it is cold and the engine has sat overnight.

I tested the number one(the front-most) glow plug and it glows cherry red when I run 12 volts through it. In the process I twisted the wire that goes to it because I couldn't get it off before hand. In order to get the little nut off I eventually noticed that I was screwing the whole post out of the plug. I tested the GP again once the post was back in and it still worked.

Now I have to splice some new wire to the number 1 GP wire. For all I know it's the only one that works.

I also had my multimeter stolen recently so I can't check them at the plug that goes to the relay.

The starter is three months old and the battery is brand new. I also have been charging the battery just in case the alternator(3 mos. old) is bad, still no cold start without some serious cranking and it has to be above 30F to pull that off.

I forgot to mention that the previous owner had upgraded to the pencil type glow plugs. They worked flawlessly last winter at temps as low as 12F. It would fire up immediately.

I have had to really crank on the starter lately so I hope I haven't weakened it. I was also running 15W40 in some very cold weather. I was low so I added about two quarts of Rotella Synthetic 5W-40 last night and ran it for about 10 minutes hoping it would thin out what was still in the engine.

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1993 W124 300D
-297K on the clock as I type this.