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124 300 td passed out after exertion, won't revive, eating battery.

isobars

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Joined
Dec 20, 2009
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925
Location
Portugal, Belgium + Lancashire
Car
300SD'79, E300TD '95, 300TDT '82, 280CE '84, 250L '84, 300SEL LPG '91, 300D '80, 300CE '91, 300E '89
I used my 1995 300 diesel to reverse a trailer up a very steep incline and it struggled, though made it over the line, and promptly stopped. I've just popped a fresh battery on it as it wouldn't so much as wink at me after the ordeal, it stated straight up so I gave it a quick run round the block, less than a minute, at the start of the journey I popped the wipers on and nothing, same with the heater. I noticed at start-up the ABS light was on, but that's happened a lot, then when I got back no gauges worked except oil pressure. I turned it off, expecting a blown fuse somewhere and tried a restart immediately, nothing, flat as a flute. I put the voltmeter across the battery and found 0.75 volts, I disconnected a terminal and got 6.85 volts.
Does anyone have any ideas, I'm picking folk-up from the airport tomorrow - perhaps!
 
surely the only way of determining what is draining current at such a ferocious rate would be to remove fuses to identify which circuit is causing the problem. I think you need to borrow a car if you are going to the airport.
 
You sure your meter is OK, as those are both unusually low voltage measurements?
 
Broken or bad connection [corrosion]on engine earth strap? Usually from engine bellhousing to nearest chassis member. Can be a braided strap, but if the round plastic covered cable design - they have been known to rust thro inside the plastic sheath.
 
Thank you all for the advice, I'll check out all the suggestions, I would love the OVP to win. The meter is OK, it's weird that if I detach the terminal it pops back up to six-ish, then drops to less than on when connected.
Thanks again.
Paul
 
Well, not the ovp, battery charged to 13 will try again and be a bit more observant.
 
Had a similar problem a few years ago and found the fault was with the alternator which had a combined voltage regulator, don't know if that may be your problem, it was on a W124 coupe. Instead of charging, it was draining the battery very quick, turn off the key, leave for about 5 minutes and it would start, then nothing.
 
Thanks Geoff,
Thought we could be on it, there, but once this goes flat it is very flat.
I took it on a run today and had different results after a bit of interference.
The thing started with a battery showing 13v, I took it for a small spin, within about two minutes the wipers had started slowing and the heater slowing. Then on popped the srs light to accompany the abs, I took it home and left the engine running with the slow wipers still wiping slowly - more slowly. I turned/twisted all the fuses in their little beds and lo, the wipers got a little quicker, I got inside the car, revved it and noticed the courtesy light gaining power, and the wipers. Cracked it, I thought, then the battery light popped on and there was no more gain. Apart from that difference, the other significant change was that the battery was the same charge connected as disconnected, in this case about 10v.
So a huge improvement, but still not charging.
I'll see if it has cured itself tomorrow.
Thanks again everyone, for all the help.
 
Sounding more and more like an alternator parasitic drain. Two possibilities 1 a problem with the combined voltage regulator/ brushes-holder [ worn brushes // electrical fault] 2 a shorted recifier diode 1 is field replaceable 2 is a complete alternator strip down . Price a guaranteed exchange unit from your local vehicle electrical specialist then you have covered all the bases. You have checked the engine earthing strap?
 
Many thanks Graeme,
Accurate and concise, as usual, much appreciated!
It's been honking down all week, I'll check the strap when there's less of a deluge - forecast tomorrow.
Cheers,
Paul
 
Whatever is draining the battery at such a rate will be getting very hot.
Does the battery drain start as soon as you connect the negative cable, ignition on or only when the engine is running?

Can the alternator be felt easily to see if it's getting hot?
 
Well, clear a path to the bottom of our stairs, the thing fettled itself. The next day it kept the charge, the day after the red battery light went out, the next four days it charged and kept it.
Let's see. Thanks for all your help. Have a Cool Yule. Cheers,
Paul
 

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