[tombiowami]

I purchased a 2016 228i a couple months ago. Loving it. I just noticed in the trunk/battery compartment maybe an 1/8" of an oily substance. It was on the bottom but also covering the little tool kit. It has no smell and is clear. Car runs fine, no warning lights.

I am pretty sure I looked in the compartment when I got it and would have noticed it.

It has rained here lately, I don't remember anything torrential, maybe water getting shot up from the road or something?

Any ideas?

[Maynard]

I recall some old threads about water leaks, either from sunroof or up from body vents - try a deep search of the threads. Would be worth taking the cladding off to find how bad things are, and where it is coming from - if it sits in there over time it can't be good.

[XutvJet]

Considering that the car is used and nearly 5 years old now, I would put money on the fact that the prior owner spilled something in the trunk. I bought my M235 new and there's trunk compartment is spotless. There's nothing that drains to the compartment.

[PDM5]

I know that you said you looked before, but I had the same issue when I used to keep a bottle of oil handy in that cubby above the battery in the trunk. The bottle wasn't open, but with the changes in temperature, some oil leaked out through the cap as it isn't fully sealed. Against the compartment, oil (especially 10W-60) looks clear and it won't really have a smell. Now I keep spare oil in that fancy little bag from BMW like a douche lol. Just figure I'd throw that out there.

[chattanooga240]

Check the seals on your rear taillights. Even a small leak could pool in the battery compartment.

[Maynard]

IIRC, there is a potential leak down from the sunroof, in from the tail lights, and I think up through the lower rear quarters (air vent?). Somebody posted about having enough water built up that it eventually shorted things, but it hides under those felt inner linings. Probably possible to have it in there for a while, and not notice it until you slosh it about with hard driving or bumps. Take a white paper towel and dip it - oil will give a distinct translucent effect, and it will help bring out subtle colors like if it is windshield washer fluid, or if there is rust in the water. You really don't want to let standing water sit, especially in seams - even the best rustproofing will eventually fail in those situations. Plus it is a great excuse to swap out all that crappy stereo gear hiding under the carpeting

[tombiowami]

Thanks for all the feedback, great forum. It occurred to me that I took it through an automatic touchless car wash a week or so prior. After looking at it some more it's a distinct solid blue. Am putting down paper towels to soak it up and take it from there.