Charging Issue 1987 300tdt - PeachParts Mercedes-Benz Forum

southherogrease · #1 02-27-2013, 10:20 AM

I've had my 87 300tdt (195k) for about 5 months and love it, but...

A couple of weeks ago, it wouldn't start after sitting at work for 12 hours. My indy mechanic found the battery discharged, swapped it out while charging the dead one and found no apparent issues. The original battery tested o.k. so he put it back in the car. I had been having tach fail/abs light stuff going on, so he replaced the OVP relay at the same time.

I drove it for a couple of days without issue and then it wouldn't start to pull it into the garage. I charged the battery up and then started driving it again, recording battery voltage with a multimeter (see numbers below if you think it would be helpful). A couple of days later, same problem. I haven't driven it since then because on that last drive home the right front turn signal assembly abandoned ship.

Any thoughts? Thanks.

Sun @1345hrs 13.49v coming off the charger
no driving
Mon@620 12.79v before start
13.87v running, before leaving for work
12.8v after 17 mile drive to work (avg 40 mph, few/no stops)
@1615 12.9v before start
12.85v after 17 mile drive home
Tues @630 12.3v before start
11.95v after 17 mile drive
@1605 12.19v before start
11.44v after 17 mile drive WON'T START

Aquaticedge · #2 02-27-2013, 10:34 AM

sounds like you have a drain happening, or maybe a grounding issue, it looks like your alternator is charging well on monday, but you diddnt post a running voltage for the rest of the days, start with the basics, Verify your alternator is charging well, clean the connections between the cables and car, make sure your terminals are clean, not fuzzy. then check your ground/Earth strap connections make sure they are clean and have a good ground. if that all checks out then look for a drain, It's a low to medium train to kill the battery in 3 days (the bad grounds could also cause gauges to go funny, so can low alternator voltage. I'd start first with verifying the alternator is working as it should)

Fattyman · #3 02-27-2013, 10:37 AM

You'll need some more running voltage readings but 13.87 is good voltage as long as you have good amps to go with it.
Without an amp reading I'm going to guess you have a drain somewhere while the car is parked.
Are you SURE the battery is good? How old is it? If it's 5 years or more look no further.

whunter · #4 02-27-2013, 10:40 AM

Tues @630 12.3v before start
11.95v after 17 mile drive

@1605 12.19v before start
11.44v after 17 mile drive WON'T START

My best guess:
* Glow plug relay random sticking on = excess constant draw.
* Failing alternator.
* Failing regulator.

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