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Old 05-04-2002, 03:41 AM
Posts: n/a
Car stall, battery dies

Ok, this has happened twice now, so I figure I should try to fix it...

So I'm sitting in my car with the engine running but parked for maybe an hour. After this extended period of time, I notice that the tachometer is starting to fall slightly, but not too bad (maybe 500 rpm). Of course, the idle is a bit rougher (as if its about to stall) but again, not too bad. The tachometer continues to fall and then all of the sudden the car stalls. The weird part is, is that the car won't start - it won't even turn over. I jumped it the first time, but I just left it in the parking lot tonight. At first I was thinking maybe the battery was dying, but why would the battery be drained when the car was running? So maybe the alternator?

Any ideas on how to fix this would be appreciated because I'm getting tired of this...

Thank you in advance.
1988 300E
1988 420SEL
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Old 05-04-2002, 05:01 AM
Ashman's Avatar
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Join Date: Sep 2000
Location: Sherman Oaks, CA
Posts: 4,749
At the back of the alternator there is a little unit that is secured in with a few screws. It has brushes at the end...

If yours are completely worn, replace them and you probably wont have to replace the whole alternator.

The brushes wear over time. Unless the bearings in the alternator have failed, the brushes might cure your problem.

'92 300CE - Sold
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Old 05-05-2002, 11:12 AM
EricSilver's Avatar
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Join Date: Mar 2000
Location: Fairfax, VA
Posts: 1,265
Did you note the engine/coolant temperature?

When my car gets hot -- after idling for long periods -- the starter solenoid won't engage until it cools off (heat + magnetism do not mix).

As for why it shut down to begin with, perhaps someone else can answer.

Eric Silbver
1989 260E
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Old 05-05-2002, 03:40 PM
hedpe's Avatar
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Join Date: Oct 2001
Posts: 507
When the car dies out, what error lights go on? Something similar happened with my 300SEL. It would die out, if you turned the key into the on position, my SRS and i think it was the ABS light would go on only, the battery light would not go on. If this is the case like ashman said, it could be that little part. It's called the voltage regulator, fastlane has them at a good price. Let me know.
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Old 05-05-2002, 04:09 PM
Join Date: Mar 2000
Location: Gainesville FL
Posts: 6,844
Well, I suppose that you were running the A/C while idling for an hour. Tunes?

Most 88 300E cars in such a condition and new original alternators will kill the battery about as fast as leaving all the lights on including entry lighting. The alternators on 88 300Es make about 20A at idle. The fuel and ignition use a good portion of that probably 15A. The A/C with aux fan will easily take 30-40A. Add it up. A set of headlights probably use 6-8A.

You are using more than you are putting back and thats all you get in 88. A big improvement can be made by buying the 1990- harness and 80A alternator. The fact that the overall output is 10A higher isn't the point. Improved alternator design has the 80A alternator making most of its output at idle speed, probably 50-60A.
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician
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Old 05-05-2002, 05:07 PM
190D22's Avatar
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Join Date: Apr 2002
Location: Columbus, Ohio
Posts: 876
So is it wise to change up to a bigger alternator? Now that better technology is out? Mine's only a puny 55A alternator and I have found a 70A for my car. What do you think?
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Old 05-05-2002, 05:42 PM
Join Date: Mar 2000
Location: Gainesville FL
Posts: 6,844
I don't know on the 190 if there is the same easy conversion as the 300E. The bigger alternator will help but the deal with the 90- 80A alternator is that it produces at low speed. Fifty five amp alternators are just fine unless you just sit around and idle all the time. A seventy is not much better if it is one of the early designs. The later alternators can be distinguished by the output terminal being screwed to a 8mm lug rather than spade type push on terminals.

What makes the deal so sweet for the 300E is that a cheap harness is available from MB (its not intended as an upgrade its just the part on the later car and it is separate from the larger engine harness) and the 80A alt is actually cheaper by a few bucks wholesale (retail it isn't).
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician
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