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Old 12-19-2002, 04:19 PM
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Join Date: Sep 2002
Location: NE
Posts: 133
Question why did I need a jump start?

Last night I was stuck in bad traffic with an 85 190e 2.3. I had been basically stopped in this traffic for about an hour. had the radio on my headlights on the defroster going full blast (I noticed that if I run the defrost at the highest temp it helps keep the engine cool in bad traffic). I had opened the window to let some of the hot air escape and I think that's all I had running. Car has a new battery and a fairly new alternator I believe. Anyway, the car starts to act a little quirky, the tachometer needle started to jump from where it was idling up to 2k and then down to .5k and back and forth, I turned off things and the car is not actually revving, just the needle has acted up. So I think, "better pull over somewhere and let the car settle and the trafic clear". So I found a spot and put up the window (Which went up very slowly). Walked away came back half hour later car wouldn't start. Got AAA involved guy came and jump started the car. He didn't have to have the cables on the batteries for more than fifteen seconds before I was able to turn on the headlights and start the car, drove it home (traffic had cleared out at this point) no problems car started right up this morning. What might cause this? The car didn't make any funny noises just seemed to lose juice. does sitting in traffic in an old car do this? how could I avoid it in the future. I usually don't get this car up past 40mph, in fact I don't think the car has ever gone faster than 60 (second owner though who knows what happened before). Any thoughts on why this might have happened, what to check, and whether I can expect it to happen again (although I am determined never to get stuck in traffic like that again, go get a coffee instead). Any thoughts would be appreciated. Thanks, happy holidays, cdt
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Old 12-19-2002, 04:26 PM
Join Date: Mar 2000
Location: Gainesville FL
Posts: 6,844
I'd say you might have a weak battery. You exceeded the output of the alternator for some period. This normaly should be handled by a strong battery.

There is a good chance that you were using 40-50 amps and the alternator probably only does 25-35 amps below 2000rpms (the pre1990 cars are burdened by this fact).
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician
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Old 12-20-2002, 07:32 PM
Registered User
Join Date: Aug 2002
Posts: 54
This is not an MB specific reply, since I never paid attention to whether my MB's work the same way as my other vehicles in this regard, but it might shed some light. If the MB is like other cars, one of the "heavy load" items that comes on when you switch the heater lever to the "defrost" position is the A/C compressor so that the air going to the windshield is de-humidified by the A/C system regardless of whether you actually want any A/C (meaning cooler) air at that time. If you're really just using the heater core and blower to augment the radiator in a situation where the motor would otherwise overheat, you'll probably find it works just as well to set the heater output to the floor or the center vents instead of defrost to avoid toggling on the A/C compressor with its additional electrical and mechanical load. Of course, if the engine heats up in traffic and you have to run the heater to keep it out of the red, there's probably something else going on worth looking at.
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