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M120, M119, W126*2 + Silver Avantgarde wagon
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Discussion Starter #1
Apologies for the perhaps obvious question:-

MB put a new battery in my W140 while they had it in storage. But in the mornings my car battery is flat. I took it back to MB and they tested and said teh battery was good. They did not have time to do more diggings. Sometimes it starts fine, sometimes it is dead, especially overnight.

I am going to find a competent wiring tech to see if he can chase down a draw on it, as I get the feeling MB is just throwing parts at this and not solving the underlying situation.

Any advice would be appreciated as I am loathe to keep jump starting an M120 for obvious reasons and it is a national holiday here so no tech is available today, and I'm keen to get this resolved so I can carry on with my travels. Many thanks.
 

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W140 Moderator
"CHRIS" Merc 92 600SEL / Sold > 93 600SE / 93 S500 / 89 560SEL / 413CDI / B180-CDI /A170-CDI
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7,531 Posts
Dosen't surprise me what MB does ,i keep on saying ,if a w140 owner wants there car butchered or parts thrown at it that are totally not required ,take it to a MB dealer .
I check that your CD changer in the Trunk does turn of when all is supposed to be of , mine stayed on with radio of , also check the Glove box light .
I'm sure you already inspected that all lights inside the cabin do turn of when you close the doors .
 

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1994 S600 Coupe, 1995 S600 Coupe
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1,697 Posts
What year? Early W140s had instrument clusters (the ones with mechanical odometers) that would go bad and start drawing a lot of current. They would still appear to work ok in some cases. Other than that, you'll need to disconnect things system by system until you find the issue.

Jon
 

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Premium Member
M120, M119, W126*2 + Silver Avantgarde wagon
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4,672 Posts
Discussion Starter #4
Dosen't surprise me what MB does ,i keep on saying ,if a w140 owner wants there car butchered or parts thrown at it that are totally not required ,take it to a MB dealer .
I check that your CD changer in the Trunk does turn of when all is supposed to be of , mine stayed on with radio of , also check the Glove box light .
I'm sure you already inspected that all lights inside the cabin do turn of when you close the doors .
Many thanks buddy - I will go check the CD changer! I cant open the glovebox, but see no glow coming from it when closed in the dark - so assume it is not that... And yes all the lights (that I can see!!!) do turn off...

It is definitely something weird as the car a few years back did the same thing and we kept changing the battery!!!
 

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Premium Member
M120, M119, W126*2 + Silver Avantgarde wagon
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4,672 Posts
Discussion Starter #5
What year? Early W140s had instrument clusters (the ones with mechanical odometers) that would go bad and start drawing a lot of current. They would still appear to work ok in some cases. Other than that, you'll need to disconnect things system by system until you find the issue.

Jon
Thanks Jon - it is a 1998 model year, so don't think it is the odometer. I think you are right that this will be a slow and steady process to discover...
 

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Registered
1994 S600 Coupe, 1995 S600 Coupe
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1,697 Posts
Here's probably the best way to find a parasitic current draw, assuming it's a fused circuit.

Jon
 

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Premium Member
'97 CL600
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2,840 Posts
I accidentally hit the back seat overhead light switch when raising the sun shade. never noticed it and ended up with a dead battery. Finally one night I happened to open the garage door and spotted the glow in my car. If you were closer I would loan you my trickle charger until you found the problem.
Anziani
 

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Premium Member
M120, M119, W126*2 + Silver Avantgarde wagon
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4,672 Posts
Discussion Starter #9
I accidentally hit the back seat overhead light switch when raising the sun shade. never noticed it and ended up with a dead battery. Finally one night I happened to open the garage door and spotted the glow in my car. If you were closer I would loan you my trickle charger until you found the problem.
Anziani
Thanks my friend - we used the trickle charger last night - but it was still dead in the morning!

Currently searching for a tech...!
 

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Premium Member
M120, M119, W126*2 + Silver Avantgarde wagon
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4,672 Posts
Discussion Starter #10 (Edited)
OK, all - we are at the tech with the M120.... the plot thickens...

So we kept the car runing this morning for about an hour or two in traffic, drives etc. to try and charge the battery and just arrived at the tech. When we opened up the truck the battery was smoking ! Why the smoking and hot ?

Also the battery is drawing 1.5 amps when off... so to speak, which seems a signifcant parasitic drain! So far there are 3 drains he has found, two of which are due to the stereo... but nothing conclusive yet as he is still working on it.

Please feel free to contribute anything that may help....

UPDATE : -

Two of the three draws were fuses # 15 and 16 (stereo related) and one was fuse # 11 - windows, central locking etc. With those two removed it was still drawing 0.87 amps - which would still kill the battery overnight, as spec is 0.05?

They also say Alternator is causing a ripple and that has now caused a bad battery cell...

Any thoughts...?
 

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Premium Member
M120, M119, W126*2 + Silver Avantgarde wagon
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4,672 Posts
Discussion Starter #11 (Edited)
Quick follow up:- Seems like I need a new alternator, as the alternator voltage output is 13.8 Volts but the amperage that it is putting out is way high...

With a parasitic draw of what was 1.5 Amps on the battery, could that have been cuased the alternator to pump out higher Amps? Or, is that a red herring and hence it's just a bad alternator. (after 175,000 miles, that's pretty fair if so...)

On a new alternator, I understand the OE M120 V12 alternator is discontinued..., but Bosch make one, Part # AL0766X, or NAPA, or other aftermarket, as I hear Bosch is not all that reliably German any more

So one question, is can I use a V8 M119 alternator on a V12? MB USA say yes, as it's the same part, but that is discontinued also.

Has anyone had any luck replacing the voltage regulators in the alternator?

All thoughts welcome.
 

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1994 S600 Coupe, 1995 S600 Coupe
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1,697 Posts
Rock Auto has several rebuilt ones to choose from, including Bosch. But are you sure it's the whole alternator and not just a worn out regulator?

Jon
 

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Premium Member
M120, M119, W126*2 + Silver Avantgarde wagon
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4,672 Posts
Discussion Starter #13
Rock Auto has several rebuilt ones to choose from, including Bosch. But are you sure it's the whole alternator and not just a worn out regulator?

Jon
Many thanks - and yes, I agree it may be the regulator(s) alone... - we shall see.
 

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Premium Member
M120, M119, W126*2 + Silver Avantgarde wagon
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4,672 Posts
Discussion Starter #14
When it rains, it pours... - well at 175,000 miles, one can't complain if this is my first major issue.

OK, so check this out - battery all dead, one cell at least dead, possibly more... & I can no longer jump start car, period!

But I closed the trunk latch manually by hand (push the female plunger part down by hand) in an effort to free up mechanism to allow trunk to lock better, and now the key will not undo the latch even by turning the key to the left. Hence, now the trunk can not shut, let alone lock.

Any ideas on how to undo the trunk latch, so I can close the turnk?
 

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1994 S600 Coupe, 1995 S600 Coupe
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1,697 Posts
Many thanks - and yes, I agree it may be the regulator(s) alone... - we shall see.
A scope on the alternator output can tell you if a diode went bad. Bad/leaky diode could drain the battery. Disconnect the main alternator lead and see if the drain goes away.

Jon
 

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Premium Member
'97 CL600
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2,840 Posts
And take a look at amazon.com for your alternator. I found the individual Bosch coil packs there for half the price that the dealer wanted. But I sure would change the regulator first
Anziani
 

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Premium Member
M120, M119, W126*2 + Silver Avantgarde wagon
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4,672 Posts
Discussion Starter #17
A scope on the alternator output can tell you if a diode went bad. Bad/leaky diode could drain the battery. Disconnect the main alternator lead and see if the drain goes away.

Jon
Thanks Jon - much appreciated.

Thanks Anziani...
 

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Premium Member
M120, M119, W126*2 + Silver Avantgarde wagon
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4,672 Posts
Discussion Starter #18 (Edited)
Many thanks to MAVA for being such a great help...

Problem is almost certainly all solved now. Will test drive and check again after 24 hours.

We put a new battery in and the parasitic draw has gone on every fuse (except two that we are still to check, as they have not been put back in yet) but more importantly MAVA kindly listened in detail and then told me 2 days ago I may well not need a new alternator even though the # 2 tech at the shop said I did. So per MAVA advice, I asked for a 2nd opinion from their head tech to do it personally as he is also a proper electrically skilled / trained mechanic - and now the alternator is fine.

Thanks MAVA, and just goes to show two additional things - one, a failing battery (ultimately became a dead cell) can cause many other issues and second, if your gut says the tech isn't the best, dont hand over $$$, find a great tech and look at the issue again.

M120 still good at 175k...

UPDATE

And just to update - no battery drain on all of system, as we checked other fuses.

So even after 65,000 miles I put on this car as 2nd owner I am fortunate to still have no major issues after the first lady drove it so very carefully from 0 -110k miles.

(It has been the more reliable and most inexpensive car I've ever had. Significant thanks again to MAVA and Stryker for helping me find a good one, and particularly MAVA who did and helped with many PPI's on it. A rare find - one lady owner...)
 
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