My 300D has been a little cold blooded lately, not wanting to start at 15-20F without the block heater. I switched to Mobil 1 5W40, and that helped quite a bit, but this morning it seemed to be cranking slowly again. I plugged in the block heater for about an hour and got is started, then took it straight to the local AutoZone for the free battery/charging test. According to their test, the battery was OK (but rundown) and the alternator was only putting out about 6 amps at about 13 volts. It appears that the charging system is working just well enough to keep the idiot light off, and to keep the battery charged on long daytime trips. Anyway, I'm guessing it's a bad voltage regulator (the alternator is about 2 years/70K miles old). I just ordered a regulator from Fastlane, so we'll see if that solves the problem. If not, I guess I'll have to buy an alternator (at least I'll have a spare regulator). I just thought it was interesting that the alternator and/or regulator can "partially" fail causing the battery to drain slowly.

they can, but there are a few other things. good grounding you already probably know, but also check the wiring to the alternator at both ends. Once I had a bad connection inside the plug that meets the alternator, another i had so much crud - sand, salt, water, oil and unspeakables in the terminal block on the inside fender. Worth checking, IMHO.

__________________
'82 300SD - 361K mi - "Blue"

"Good judgement comes from experience. Experience comes from bad judgement."

listen, look, .........and duck.

Good points, I'll give everything a good look when I replace the voltage regulator. I think all the connectors are pretty clean, but I'll double check.