More mysteries in the Charging System (1985 300D)
 

Seasons Greetings, All!

My 1985 300D has a ghost in the charging system. My alternator is a new Bosch, new voltage regulator and the battery is new as well. I can drive around for days during the day with no symptoms. It would seem the battery maintains its charge just fine, and then the battery will suddenly turn up dead, usually at night. I'll run an errand, come out and the car won't start, after driving fine for a week or so, day and night.

I did tests on the system yesterday and everything looked fine. Results similar to this morning's tests below. I drove the car for three miles, checked voltage at the battery with the car running (idling, at 2000RPM, with headlights, without) and the highest reading I could get was 12.4 volts.

Could it be an intermittent short?

The battery light on the dash illuminates, and here are my multimeter tests:

Car Off cold: 12.12 volts
Cold Idle: 13.6 volts
1500 RPM cold: 14.25 volts
Warm Idle: 14.3 volts
1500 to 200 RPM warm: 14.4 volts
Idle w/ high beams: 14.04 volts
Idle w/ high beams + blower: 12.05 volts
2000 RPM w/ high beams + blower: 13.9 volts
Idle w. high beams + fog lights + blower: 12.03 volts
Car Off after 15 minutes of testing: 12.4 volts

Thanks for any input...

Chip

I had a similar issue, it turned out to be a bad connection inside the plastic connector on the back of the alternator. The wires were almost disconnected from the connectors inside the plastic piece. I figured it out by wiggling the cables and watching the voltage fluctuate.

... your blower motor is toast. pull it soon.
your car can catch fire and end it's own life if you wait too long.
also, your battery is not full, and it may be bad. have it tested ASAP. you should be reading 12.7 or better on a fresh charge with the car off.

Why?

I'm guessing he says that because is seems to drop the reading 2 volts when idling, although it only drops it .5 volts at 2000 RPM.

If you could elaborate, I'd appreciate it.

I'll check that again. I actually did wiggle that connector and saw no fluctuation in the reading, but it's worth another wiggle.

It might not be your issue, but it stumped me for a while until it got bad enough to be obvious. If you want to be sure, remove it and take a look.

Are the pulleys in good shape??? If they are shiney in the bottom you can not tighten them enough to stop the slipping.

I've got a similar problem that I'm sorting out. While driving at night (headlights on, blower on) the "antilock" light comes on and all my lights get dim. When I turn off the blower everything goes back to normal. I just did my testing and the blower drops the volts by about 1.5 My blower has been making a lot of racket lately and it probably is the culprit. BTW, everything getting dim last week made me immediately suspect the alternator so I changed it. Next night I drove, same problem. Oh well, at least I have a new alt now. Let me know what your solution is to this problem. Is the blower motor able to be fixed, lubed, reconditioned? Thanks

Is it possible that sometimes your glowplug relay is sticking on?

Assuming alternator problems, what is the advisability of installing one of those single wire type alternators? I know it isn't pure Bosch, but sometimes a guy has to do what he has to do.

Not a single wire type but I have a Delco Alternator on my Volvo. The origional is an SVD of something like that; it was not a Bosch.
Mounting it was not 100% good as it is hard on the Belt due to some misalignment.
However, I have been driving since 1993 like that.
But, how it mounted was similar to the Delco.

If you can fabricate a good Bracket for a Single Wire Delco I but you could sell some.
The trick is to the older Delcos are larger; and to a lesser extent the pulley size/grooves.

I currently have a 65W denso alternator in my 300D, it's been doing well for 100K+ miles.