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      01-22-2021, 07:59 AM   #1
2000cs
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Rust? No, Cosmoline

I just washed my M5 (2018 bought new in Sept 2018, 8500 miles, always garaged, hand washed, ceramic coated). While drying the doors I noticed a small spot (triangle) of rust? at the bottom of the front passenger door, front edge, inside. The bottom front corner of the front door. I checked the other door and it is the same: surface rust? showing on the bottom, front corner from the inside of the door.

Is this common?

Has anyone had BMW repair under warranty?

Mods: after searching and finding nothing I decided to post here, please move to appropriate sub forum if this ain’t the place.

Last edited by 2000cs; 01-22-2021 at 09:21 AM..
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      01-22-2021, 08:02 AM   #2
AHall
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That is odd, in what part of the country are you located?
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      01-22-2021, 08:25 AM   #3
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Quote:
Originally Posted by AHall View Post
That is odd, in what part of the country are you located?
Have been in central KY (never driven in snow or on salt), now in Florida on east coast. I keep it very clean and hand wash and dry thoroughly whenever it shows dirt. Always garaged.

I’m going to check to be sure it isn’t cosmoline...
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      01-22-2021, 09:19 AM   #4
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It is a hard spot to get my fingers into, but with a bit of effort I was able to scrape some off and examine it more closely. Pretty sure, and relieved, that it is cosmoline. In my experience cosmoline is yellow, and this is brown and very much looks like rust. But maybe they use brown cosmoline or it darkens with age.

Weird that it just showed up there now, must have slowly oozed to that spot. I can’t clean it off, but I suppose it won’t hurt anything as long as it doesn’t block the water drains.
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      01-22-2021, 10:53 AM   #5
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I have that too. I thought it was rust and was worried maybe it was in an accident since I bought it used but then I noticed all 4 doors have it.
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      01-22-2021, 12:10 PM   #6
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Post a picture of what you are talking about
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      01-22-2021, 12:13 PM   #7
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Quote:
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Post a picture of what you are talking about
+1, would like to check my car.
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      01-22-2021, 12:22 PM   #8
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5 series doors are aluminum if i recal correctly.
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      01-22-2021, 12:24 PM   #9
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Cosmoline.... grease? Isn't cosmoline used with guns?
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      01-22-2021, 12:54 PM   #10
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Quote:
Originally Posted by MA///M5 View Post
Cosmoline.... grease? Isn't cosmoline used with guns?
Cosmoline is a greasy stuff that is used to prevent corrosion/rust. Porsche has used it for a long time on engines, so they have that yellow hue unless it is washed off. I didn’t know BMW was using it in the doors, but apparently they are.
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      01-22-2021, 01:16 PM   #11
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I think this is on my car as well. Assuming normal occurrence. Garaged everyday.
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