I had a similar problem recently......but, I am mostly likely dealing with much warmer temps......just under 40 degrees. I ended up having 2 problems.

My glow plug relay was bad, even though the glow plug light did come on at the dash. It came on, but for much shorter time period than it should have. The relay looked fine on inspection and it's fuse was fine. When I took it out it to put a "junk yard car's" on, I realized it had oil dripping out of it (just got the car over the summer). Once I had that fixed......immediately I had the dash warning lights stop working, but the dash glow plug light worked fine. Then I replaced the voltage regulator and everything worked the way it should. I too was having the "cranking" issue and my battery didn't seem to stay charged, but the "battery" dash warning light was lighting up so dimmly I couldn't notice it unless it was dark outside.

Just an idea...thought I'd share my experience.

My autozone didn't have any 0w-40 ro 5w-40. Would 5w-30 be alright or should I find something else. I just got a brand new battery from them at no cost too so I'm pretty excited about that. My voltage regulator should be here by tommorow so I'm gonna hook everything up then and be back on the road. Someone please let me know about the 5w-30 oil though. thanks

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W126 1983 300SD 286,000 miles and ticking
Baby blue exterior Grey MB tex
Recent work:
Replaced air cleaner mounting brackets and heat shields
Replaced alternator, fan and power steering belts
Replaced positive battery terminal
Replaced negative battery terminal and cord
New Duralast Battery

My car needs work.

No, too thin..
You need 0w-40 or 5w-40 synthetic.
The phone book is your friend, any major auto supply, truck stop or oil supply company can get it.
Try Wal-Mart also...

For the climate in Washington, DC, you probably can get away with 10W-40. It's much easier to find than the grades Roy listed. Make sure it is a diesel rated oil. It will have a "CH" or a "CI" designation on the container.

Thanks Brian. So I just put the new battery in my car. I went inside to turn it on and put the key in the glow plug position and nothing happened. The light dimmed so much that it was almost off and the dash lights didnt really come one. I tested the battery and it read 10.6 volts. Don't really know how that happened but I will be going back there tonight

__________________
W126 1983 300SD 286,000 miles and ticking
Baby blue exterior Grey MB tex
Recent work:
Replaced air cleaner mounting brackets and heat shields
Replaced alternator, fan and power steering belts
Replaced positive battery terminal
Replaced negative battery terminal and cord
New Duralast Battery

My car needs work.

OK, there is a "leak" in the system.

You need to disconnect the negative battery cable and install an ammeter in series between the cable and the battery post. Close all doors and see what the ammeter reads. It must be below 100 milliamps (preferably less than 60 milliamps). It probably will be higher than this amount. Start pulling fuses, one at a time, until the meter drops down.

If it never drops down, even with all fuses removed (a definite possibility), then remove all the wiring from the back of the alternator. If the meter now drops down to zero, the problem is a current leak internal to the alternator.

Dead short???
Did you get a fat spark when you connected the new battery?
Did the battery terminal or cable get warm when you connected the new battery?
The starter never cranked?
Are you saying the new battery was reading 10.6V under three minuets?

This sounds like a bad new battery or a massive dead short.

A massive dead short:
* Glow plug relay contacts welded closed.
* Alternator or wire short.
* Starter shorted.

I missed the fact that there was no time interval involved after the battery was installed and the voltage was reading 10.6V.

Therefore, the advice given by WHunter in the above post should be followed first.

You don't have a small current leak. You either have a bad battery or a dead short, as mentioned above.

The remaining possibility is terminal clamps that are in poor condition. Did you take the voltage measurement directly on the battery posts or on the cable clamps? It's possible to have a slight voltage drop across the clamps, but the clamps would need to be in very bad conditon for this to occur with low load.

It was a bad battery. I got another one tonight and it started up after a lot of cranking. It took the thing forever to turn over on its own. it was basically running but the starter was turning it over kinda. Dont really know how to explain that. Anyways it finally started and I checked the voltage at the battery terminals with it running after I put on a new voltage reg. and it read about 14.1 volts so hopefully my problems will be cured after I get some good fresh oil in there.

__________________
W126 1983 300SD 286,000 miles and ticking
Baby blue exterior Grey MB tex
Recent work:
Replaced air cleaner mounting brackets and heat shields
Replaced alternator, fan and power steering belts
Replaced positive battery terminal
Replaced negative battery terminal and cord
New Duralast Battery

My car needs work.

Best guess:
* Bad starter = cranking too slow.
* Air leak into fuel system.

Your starter should crank notably faster than a gas engine starter.

Please read this thread.

Is starter health important to your diesel?
http://www.peachparts.com/shopforum/showthread.php?p=1059687#post1059687

The car started up very strong this morning after taking all of your advice. It took about a week for me to find and do everything but it is welll worth the effort. I ended up getting a brand new battery, tighterning one of the bolts on the #5 glow plug, putting in a new voltage regulator and changing the oil to mobil one 0w-40. thanks a lot for all of the help and it feels good to be back on the road again.

__________________
W126 1983 300SD 286,000 miles and ticking
Baby blue exterior Grey MB tex
Recent work:
Replaced air cleaner mounting brackets and heat shields
Replaced alternator, fan and power steering belts
Replaced positive battery terminal
Replaced negative battery terminal and cord
New Duralast Battery

My car needs work.

Excellent news.

Help is what we do here.

That is great news.