black dots on rear bumper and the trunk (warranty case?) - The Unofficial BMW M5 Messageboard (m5board.com)

sergiyz · 19th November 2003, 02:58

I've once posted a question about black dots on the rear bumper which I've found recently on my car.
I thought that was some stuff flying off the wheels, which would
come off easely.
Well, it didn't and a dealer couldn't get rid of them (dots) either.
They had no idea where it came from, neither did I.
But after thinking about it some more I came to the conclusion it (whatever that subsctance is) could only come from the exhaust pipes or from a battery compartment.
The sides are clear, so is the front, it's only on the back and right above the pipes (bumper, trunk) and nowhere else.
It's something that could stain the paint, and that would be
coolant (coming from the engine) or an acid (from the battery).
The engine looks fine (was serviced recently), but I didn't understand how acid could come from the battery compartment.
Apparently, there's a drainage pipe on the bottom of that compartment behind the right exhaust pipe and behind the bolts holding the rear bumper.
When I looked at it, I was really surprised.
The bolt was covered with a white subsctance and the paint around it was all black too.
Then there were stains all around it going up.
So, what I think has happened is that battery has overflown and acid was dripping from that drainage pipe then spread all over the bumper and trunk lid by turbulance

I'm gonna see the dealer some time this week and show it to them, but I would like to back my case with additional facts.
I've noticed couple of similar posts on the board, so in case you have paint discoloration issue on your rear bumber, could you please check under the rear of the battery compartment for the signs of acid escaping (white "powder" of bumper bolt, black stains around it etc) and such ?
I suspect I'm not the only one...
If you do find the same sympthoms, please reply here or send me a private message.
If you're in the Bay Area (CA), we can even arrange a nice meeting at SC BMW or whatever the dealer of choice will be

p.s. I'm gonna post the pictures later, so it's easier to understand what black dots I'm talking about.

thanks

TCM · 19th November 2003, 06:33

From your description, I would also put my wager on battery acid dripping out of the drain plug underneath the trunk. Please let us know how you make out.

sergiyz · 19th November 2003, 09:38

It definitely looks like it.
Why the battery has leaked is a good question though...

Some pics as promised:

thanks

Quote:

Originally posted by TCM
From your description, I would also put my wager on battery acid dripping out of the drain plug underneath the trunk. Please let us know how you make out.

TCM · 19th November 2003, 17:15

Wow, that is really bad. I have never seen an M5 battery drip like that before. I would definately complain and try to get this repaired under warrenty. Good luck.

M-Fünf · 19th November 2003, 18:01

Wow, Serge, that looks horrible

It definitely looks like the overflow tube allowed some acid to come out. Must have been while you were driving to get back on that bumper screw...and on the back of the car...

You can test that white chalky stuff to see if its acid by removing some of it and testing it with a solution of baking soda and water...(just like cleaning battery posts). If it bubbles, it's acid. This white material (if it's what I think it is) will also have a very distinctive (metallic) smell.

I'm sure your dealer will fix this problem, but more importantly, they need to fix the CAUSE of the problem! I believe that this is a sealed battery, so what would cause it to overflow? Maybe voltage regulation in the charge circuit is bad? You don't live in an extreme environmental area, so that's probably not an issue...it's a real quizzer...

Good luck, Serge

sergiyz · 28th November 2003, 21:51

So the dealer looked at it and agreed that was a problem with the
battery vent line.
A guy from BMW NA looked at it too and said he's seen this before.
From his explanation prev. models had a liquid separator on the vent line which prevented acid from escaping.
Nowdays they're using a different kind of vent (actually they've changed the angle) which they thought wasn't prone to the escaping acid problem.
Apparently, they were wrong, so they are installing liquid separators on cars where the problem has shown itself.
They've also told me the battery doesn't have to boil for liquid to escape. They've tested the alternator and the battery itself and they both turned out OK.
Anyway, they are gonna repaint the affected areas.
Good thing, since otherwise it would cost several thousand $$.
The bad news is I have to live w/o my car for another week or so.
BTW, if you own a 2001 car you may also have to install a new control unit for the airbags.
This is the latest recall affecting all e39 cars (not just the m5).

TCM · 29th November 2003, 00:40

sergiyz:

I am glad to see the dealer is stepping up and taking care of this. Thanks for the information about the battery. I have seen a couple M5s drip a little acid now and then, but nothing like what you had. I guess I will have to keep a closer eye on the vent tube when under the M5.

Jim Dolan · 29th November 2003, 01:54

I have the same dots on my bumper, 2000 model but I don't think it is caused by the battery. I first noticed it after a run at Sebring so my take if turbulence damage. I remember the early testing of the M5 in the north of Europe where the cars rear was plastered with snow from it. What I don't get is the lack of dings or damage. This may be because the bumper is plastic and gives a little. I'll speak to the SA the next time I get service.

sergiyz · 29th November 2003, 05:52

It's rather easy to check, look under the bumper, especially at the
bumper mounting screw and around it.
You will see right away if it's the battery acid.
It the sides of the car are clear, there's not too many places it could come from.
When you talk to your SA, make sure he looks under the car, you have to kneel for that, otherwise you won't see the vent of the source of the damage.
You can use the pictures I've posted as a reference.

Quote:

Originally posted by Jim Dolan
I have the same dots on my bumper, 2000 model but I don't think it is caused by the battery. I first noticed it after a run at Sebring so my take if turbulence damage. I remember the early testing of the M5 in the north of Europe where the cars rear was plastered with snow from it. What I don't get is the lack of dings or damage. This may be because the bumper is plastic and gives a little. I'll speak to the SA the next time I get service.

ernie · 29th November 2003, 06:08

jim,

have you tried a clay bar? if not, give meguairs clay bar a try, it should remove it.

ernie