Can anyone tell me if it is a normal quirk for a
'82 300SD to drain the battery in about a month of no use? Mine will only hold a charge
for about a month before the battery is dead. Anyone have the same problem?

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82 300SD 100K
91 Caprice SS
92 Jetta TD

One month seems likje a very short time. Sounds like your battery is just getting old. Do you know the last time it was replaced? There is also another thread on Battery drain with some very interesting safety commnets - a MUST READ! If it works fine with daily use, I would guess your charging system is fine. Youcan confir this witha voltmeter (13.5 volts or so).



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Deezel
87 300TDT
150,000 miles

One real problem in analysing charging problems on early 300SDs is that they are way undercapacity on the size of the alternator. The first models had an AL 80x (Bosch rebuilt #) which only puts out 55amps. Later models, around 83 and up, had AL 117x models with 65amps. The problem with these alternators is that they don't produce that number till about 2000rpms. At idle they make about 20-25amps. The newer cars are above 120amps and they get 90% capacity at idle (good stuff).

Unfortunately the A/C with aux fan running takes about 25amps. So if you are idling with your A/C on and the wipers and headlights going you are about 25amps in the hole. Combine this with the high losses during glowing and starting and short, stop and go, trips and you have a problem. We see 10-20 cars a summer that the driving conditions cause the problems not a lack of original performance.

We no longer ever use the AL 80x. We replace them all with AL 117x, but it only helps marginally. I don't do the exchange on working systems only when the alternator is bad.

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Steve Brotherton
Owner 24 bay BSC
Bosch Master, ASE master L1
26 years MB technician

I have a new battery. The charging system is fine it is only when the car sits for a month without running that the drain occurs. Any ideas?

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82 300SD 100K
91 Caprice SS
92 Jetta TD