Hello all! new member, crazy story! melted battery post! - PeachParts Mercedes-Benz Forum

1911diesel · #1 04-11-2013, 11:55 PM

Ok, first off let me say hello to everyone, and that this will be a fairly long post, sorry. also i am not new to diesels or mercedes diesels even. i have owned 4 mercedes diesels now and this one, well its starting to make my head hurt...

Ok 85 300sd, paid 1200 bucks about 2 months ago, came with a spare mw injection pump, a spare tranny, (which i thought was awesome because the 82s tranny is slipping) and a spare vacuum pump. super clean body. one dent in the drivers front fender but no big deal. no real rust (ill post pics later its late and i work tomorrow) not much clear coat peal, tinted windows. most of the windows worked! lol (if you have owned many you know thats a big deal!) sun roof worked! the engine (i was told) was just changed because the old one snapped a timing chain. (the spare parts came from the 81 300d that was the parts car.) oh it needed a head light and a break light and some other little things... so i was told... well i been buying and swaping and trading cars for a long while now, i know there is always more then meets the eye or is said when buying a used car. so i kinda figured there was more but it was cheap and super clean! (the 82 i like to call my soon to be parts car...windows work when they want to, gauge cluster works when it wants to, sun roof does not work, body is kinda rough, paint is fading bad, tranny slips but it runs great! oh interior is kinda rough.) so we picked it up knowing i was going to work on it. well first things first, the alda was broken... now its removed. (oh by the way it smoked black at idle before the alda was removed im still trying to figure that out...) the waste gate was stuck open, just a little. made for slow boost response. now its working properly. i think it needs ball joints. not sure havent gotten that far...lol but the thing that im having the most problems with, is this electrical demon. i know it has to be a ground somewhere.

Ok problem i need the most help with at this moment, where to start...lol well it has killed 3 batteries now. the most recent battery it melted, yes i said melted the positive post. the battery before that it just killed the cells, ( 24 hour 2 amp charge and still not taking a charge battery was replaced, the battery that is melted was this ones replacement) and the one that came with the car died about the second or third time this problem struck. Ok the problem is that when we start the car, or attempt to start the car, sometimes not always, only once every three days or so, it will completely discharge the battery. sometimes it will start, sometimes it wont. if it starts and the battery is discharged nothing electrical will work. if it doesnt start, most of the time the battery would come out of the discharge with a slow over night charge. now the real crazy part is that sometimes, the seats will move on their own! while she is driving! i found one ground problem, it was the bottom starter bolt, that wasnt threaded to the starter. It is now tight and that ground is tight. I thought i solved the problem with the starter ground. this last battery that melted, is the result of my assumption. i have had similar problems with my ford. bad starter solenoid killing batteries, and a bad starter armature grounding itself and killing batteries, but nothing ever this extreme. am i safe to think i should be looking for a failure some where between the starter and battery and the main grounds. with the amount of amperage it took to melt the battery post it has to be a large gauge wire grounding. otherwise i would imagine it would have been the wire fried and not the battery. or fuse or solenoid or something else would have failed before that point. Oh and it only discharges the battery when trying to start. the alternator still puts out 13.7-14 v.

Im starting to think the car just doesnt like her... it doesnt do any of that when im driving it or starting it. just my ol lady.

FYVMMF · #2 04-12-2013, 12:42 AM

The two basic high amperage connections to the battery positive terminal are the starter and its solenoid and the alternator.

Sounds from your starter description that there is something causing intermitent operation.The solenoid is controlled by a seperate small gauge wire, when it is energized it does two things, it mechanically operates forcing the starter gear out to engage the flywheel and nearly simultaneously operates an high current electrical contact set the electrically energizes the starter causing it to turn its gear and in turn the flywheel.

It sounds as though you may have a problem with the solenoid's electrical section shorting to ground. There usually is a high current conductor between the solenoid body and the starter body, it is possible that there is something shorting that out. Could be something failed inside the solenoid body or harder to envision but something inside the starter body.

I seem to recall that there is usually not a ground connection on the stater/passenger side of the 61X engines, I recall the flat bare copper ground strap being on the driver side between a bolt on the bell housing and the frame behind and underneath the steering gear.

With the alternator a failure inside the alternator of the diode could enable a reverse current flow that will quickly drain a battery, but I would concentrate on the starter and solenoid mainly. It would be practical to disconnect the alternator wiring at its junction connector up on the passenger side wheel well just to eliminate it from the equation.

davidlee · #3 04-12-2013, 01:42 AM

Hello, welcome to the forum!

marco5 · #4 04-12-2013, 01:46 AM

Welcome!

benedict · #5 04-12-2013, 06:21 AM

Whilst the posts are lead and have a low melting point, there is some serious current to be melting your battery post or the batteries are of sub standard quality.

Have you been doing some long cranking?

Start from the beginning.Check resistances from the post(s)
I'm assuming you have already cleaned the terminals-make sure your starter solenoid cable and/or alternator cables at the positive battery post have lugs that appropriately fit the bolts and that the nuts are tight. I've seen lugs that were too large for the bolts so only a small portion was able to be crimped down.

If all is tight, check them. Set your multimeter to ohms--> put one meter lead on the very top of the battery post and the other on the end of your negative cable wherever it attaches to the chassis--> you should get a reading of .1ohms or less.
Keep your meter leads in the same position but set your meter to DC volts-->turn on your headlights (accelerates voltage drop) --> you should get close to 0.0volts or in the millivolts vicinity.

If this is ok then follow your positive cable down to the starter motor and make sure the insulation is good and the cable is not snagged on metal somewhere.
Also check the smaller positive cables going to the alternator and starter solenoid ( if it is separate).

It is possible but not likely that the starter is at fault. If it was getting stuck on you would hear it! If the starter solenoid contacts welded together then you would also know about that!

Pictures of your batteries can help to get a good picture of what is happening.

Walkenvol · #6 04-12-2013, 07:48 AM

Your confident the battery is secured and not moving around and grounding on the car? Its a pretty tight area in there.

1911diesel · #7 04-12-2013, 08:46 AM

no excessive cranking. the car starts on the first crank every time. if the starter works. lol it smokes a lil black at idle and knocks kinda hard, not sure if i should retard the timing or advance it. the 82 smokes a little white at idle most of the time, but there is no air in the lines, and it is quite as a mouse. i think im going to advance the timing on it.

first thing i need to do with the 85, is try n replace the battery...lol ill work on that today or tomorrow, i dont know if sams club will take it 3 or 4 days after i just replaced one... and this one is melted! lol. if they take it back ill be saving $100 bucks and be able to drive my truck, i took one of the new truck batteries out of my truck to work on her benz.

the bottom dropped out of the weather here, so its cold again. when it warms up a little ill pull the turbo back off, ( engine mounts need replaced as well and if im messing with all that it will be easier.) and pull the starter off and see if there is a problem with it. i have rebuilt starters before, and if i have to ill but a new solenoid. after the battery is replaced and i checked the starter out ill go back thru the connections with a volt meter.

thanks for the warm welcome guys. i really just wanted some back up on what i was thinking. my dad is pretty sure it has to be somewhere between the starter and battery as well. ill try n get some pics of both benzs here soon we have some i just have to find them.

t walgamuth · #8 04-12-2013, 08:57 AM

I am no electrical expert but that would seem to have to be a dead short to melt a post.....I'd look at the positive cable and trace it down to the starter and see if there is a place its rubbing itself bare....next I'd look inside the solenoid for a dead short.

vstech · #9 04-12-2013, 09:09 AM

nope. a dead short would have melted the cables, and exploded the battery... I've seen it happen.
I have also melted battery terminals, the starter is MORE than capable of drawing enough current to do this.
I'd start by disconnecting ALL electrical feeds. disconnect the starter, the alternator, and the fuse panel feed.
then connect JUST the starter, and see if it draws current. then engage the starter, and measure the ampdraw of the starter. (it helps to have a clamp on DC amp meter)

t walgamuth · #10 04-12-2013, 09:35 AM

I exploded a battery once.....frightening!

1911diesel · #11 04-14-2013, 03:20 PM

Ok so little update, sams club replaced the battery, (note to self buy more batterys from sams) and it has warmed up here in terre-able haute. so i am working on the benz. here is a pic of the turbo off, ( came back off because if im going to work on it again im going to change the engine mounts as well.) and i am about to pull the starter off. ill post some pics.

first the 82 300sd

the 85 300sd

some under the hood and turbo pics

the destroyed engine mount.

and im about to pull the starter off and take it to the zoo, auto zoo, for testing.

1911diesel · #12 04-14-2013, 03:56 PM

ok so quick update, got some pics of the cars.
the 82 300sd

the 85 300sd

1911diesel · #13 04-14-2013, 04:30 PM

i think i figured it out! starter solenoid power post, the one that should have a nut holding it tight in place and one holding the wire on. well it only had the one and it wasnt as tight as it should have been to keep the post from moving around. i have the starter tested anyways and it tested out fine 3 times, in a row. im hoping putting another nut to keep the post solid will solve this problem. i had a similar event happen with my ford but the post was stripped. so i just replaced the solenoid. but autozoo said they want 83 for a starter and 93 for the solenoid! ill just try n fix this one first.

1911diesel · #14 04-14-2013, 04:31 PM

i also posted pics and a little more back round, but it hasnt been approved yet i guess...

vstech · #15 04-14-2013, 10:40 PM

I see the pics, let me know if anyone has any trouble with the pics.

the 82 is identical (right down to the peeling paint) to my 82, and my 85SD. I really like that color.

I'm glad you found the issue with the starter, I REALLY hope you don't install a autozoo starter... it's not easy to change the starter, so only do it once if it's needed... use OE!!!
the bosch rebuilds are great. (pulls from the yard are better in my opinion!)