I have a 1984 mercedes 300D (European) I have had some problems with my battery lately. It seems like the alternator is not charging the battery. It will be running fine, and then out of no where it won't start. The first time it has happened I thought it was just that the battery had died, but then after getting a new battery it died again about three weeks later. I got a new battery again and the same thing happened again. I am not really sure what is going on. If anyone has any idea please let me know.

Did you already post this in "Tech Help"?

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2009 ML350 (106K) - Family vehicle
2001 CLK430 Cabriolet (80K) - Wife's car
2005 BMW 645CI (138K) - My daily driver
2016 Mustang (32K) - Daughter's car

Diesel Discussion would be the best place for this.

Have you put a meter to the battery with the engine running and not to determine whether the alternator is working?

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Whoever said there's nothing more expensive than a cheap Mercedes never had a cheap Jaguar.

83 300D Turbo with manual conversion, early W126 vented front rotors and H4 headlights 400,xxx miles
08 Suzuki GSX-R600 M4 Slip-on 22,xxx miles
88 Jaguar XJS V12 94,xxx miles. Work in progress.

use a multimeter in the 2-20volt setting to do this test--

test the voltage across the two terminals on the battery.

-with the car not running, the voltage should be exactly 12.6volts (6 cells at 2.1 volts per cell)

-with the car idling, the voltage should be in the 13 volt range (anywhere 13.xx volts is good)

-with the card idling, turn on the headlights, the voltage should not be BELOW 12.6 volts, if that is the case then the alternator is not charging

- if the voltage goes above, say, 14.3 volts at any time then the alternator is overcharging (equally bad)

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Ben
1987 190d 2.5Turbo

8 out of 10 times it is your voltage regulator that has gone bad. The brushes are worn. This is about the easiest replacement part you can do yourself. The voltage regulator is on the back side of the alternator. Two screws are removed, VR comes out, new one goes in with the two screws. No wiring to mess with. VR can be had for less than 25 bucks.

Next time, you can go to "diesel discussion" or "tech help" and get all the answers you need for problems with your car.

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"Life is tough...it's even tougher if you're stupid." John Wayne


Dave
Pawleys Island, SC

'79 300CD

How about a mod moving this thread to DD ??

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Grumpy Old Diesel Owners Club group

I no longer question authority, I annoy authority. More effect, less effort....

1967 230-6 auto parts car. rust bucket.
1980 300D now parts car 800k miles
1984 300D 500k miles
1987 250td 160k miles English import
2001 jeep turbo diesel 130k miles
1998 jeep tdi ~ followed me home. Needs a turbo.
1968 Ford F750 truck. 6-354 diesel conversion.
Other toys ~J.D.,Cat & GM ~ mainly earth moving