W124 E300D severe battery drain!

SilverSaloon

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1994 W124 E300D Estate, 1985 R107 280SL
Hi

suddenly (without any new additions on the car recently), my W124 estate has developed a really severe battery drain. If I leave it for about 6 or 7 hours locked/unlocked it will drain the battery completly dead - not even enough power left to crank at all.

I've connected a multimeter between the battery + and the connector and it says its pulling 12.3 from the battery.... even after i pull out ALL the fuses out the fusebox in the engine bay. I even fully removed the radio (just incase) but still it pulls the 12.3. The most change I get from removing the fuses is about 0.1.....

Any ideas? Are there any other fuses I can test for or any other test I can do.

Its really annoying as everytime I leave the car now I need to pop the bonnet and disconnect the battery, which I've been doing for about a week, so I know the battery is charging OK and holding charge.

thanks for any advice!!

Derek
 

balge

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Hi
had to do this a few times now, I found this link How to Find a Parasitic Battery Drain - wikiHow
and sorted it that way. Also had a battery that would appear to be ok, charging fine and holding a charge, but not enough to actually start the motor every time, that was the brushes too, but you need to check 'cold cranking Amps' not just the Voltage.

cheers!
 

ianjay

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Hi Derek.
I had a similar problem with a 5 series BMW, fully charged at night, totally flat in the morning.
After changing 8 different computer units, it was finally traced to a short where the main power cable from the battery went through the bulkhead to the fuse box.
The rubber grommet had perished and allowed the cable to rub on the sharp edge and go to earth.
It was only a tiny break in the cable insulation, but enough to flatten the battery over a few hours.
So check the cables for wear marks and tape up as required.

Cost of repair to the BMW was £2.50 for parts, but £580 labor!!!
I charged the battery and traded it in for a Star!
Best move I ever made!
Ian J
 

grober

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Alternator rectifier pack on the way out/leaky ? ======12.3 ? is that voltage? units of measurement required please :confused: You need to measure the current drain by putting an ammeter =voltmeter set to amps dc] in series with the main battery positive connection- start with a high setting normally 10A DC + don't have any high loads active. If the readings are low move down cautiously to the milleamp range.
 

Tiff

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Easy and foolproof way to go.

Disconnect battery earth lead. Connect a lamp between earth lead and earth terminal on battery. Lamp should be off or very dim if there is no draw. If its bright you have a drain. Go round unplugging things 1 by 1 until the lamp goes out, and you have found the problem. Start with the alternator as Grober said- sounds like it could be the culprit..
 

bolide

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The glowplug relay would be another place to look. There is a limited number of things on an E300 Diesel that can drain a battery fast without "magic smoke" appearing

Nick Froome
the independent Mercedes Estate specialists
 
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SilverSaloon

SilverSaloon

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Thanks - i'll retry the multimeter test (as i connected it to the POS terminal) rather than the negative.

i'll also check out the alternator.
 

Ted

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As Grober says it looks like you have the voltmeter in series with the battery. Not a good way of testing current drain! If you do as he says it should lead you to the source of the problem.
Tiff's suggestion is also a good one which I have used before. One caveat is that if there is a legitimate occasional current drain the bulb may not pass enough current for this. The bulb method is also highly visible, so you can ferret around looking for the issue.
This is also a great method for investigating short circuits - bulb on bright = short circuit, bulb off or dim = no short circuit.
Another advantage to a bulb in series while you investigate a short is that you cannot damage wiring or components, as the bulb will limit the current flow.
 
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SilverSaloon

SilverSaloon

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1994 W124 E300D Estate, 1985 R107 280SL
Just had another look at this.

when i connect the battery neg lead after removing it nothing is heard.

however when i REMOVE the battery neg lead i hear a relay go "click clock".

does this mean a relay isnt working correctly? i've not removed the relay box lid to see what relay it is yet..... which is my next step

it seems like the relay needs to "click" when i connect the battery and "clock" when i disconnect it.... if you know what i mean!!
 

trapperjohn

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it seems like the relay needs to "click" when i connect the battery and "clock" when i disconnect it.... if you know what i mean!!

Not using crocodile clips are you:devil:

I'll get me coat.
 

Danny DeVito

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Easy and foolproof way to go.

Disconnect battery earth lead. Connect a lamp between earth lead and earth terminal on battery. Lamp should be off or very dim if there is no draw. If its bright you have a drain. Go round unplugging things 1 by 1 until the lamp goes out, and you have found the problem. Start with the alternator as Grober said- sounds like it could be the culprit..

Thats a quality piece of information right there ! :rock: Straightforward and foolproof (guarded use of this phrase;))
 

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