Stains on under tray (Update: leaking ac compressor)

I have noticed some stains on the under tray after long drives. The car is a E86 N52. It's at the front of the engine below the vibration damper.



I can't figure out were it comes from and if it is oil or something else?.
I have checked the regular places for oil leaks;
Oil filter housing is nice and dry.
No leaks from the valve cover (usually starts at the back of the engine anyway).

The serpentine belt looks dry. So doubt it comes from the top of the engine. Front of the engine looks dry, although dirty.
Oil level has been at the top mark (electronically checked) ever since last oil change (May 2020).

Is it something to be worried about?

Update in this post.

Well I can't help exactly, but the first thing I thought was what is that big crack towards the top right of the photo?
I hope it's a trick of the light.

enuff_zed said:

Well I can't help exactly, but the first thing I thought was what is that big crack towards the top right of the photo?
I hope it's a trick of the light.

Click to expand...

Thankfully it's the light (flash was used) that plays trick. You can just about see the head of a inverted torx screw. I think it's the bracket holding the generator?

fredej said:

enuff_zed said:

Well I can't help exactly, but the first thing I thought was what is that big crack towards the top right of the photo?
I hope it's a trick of the light.

Click to expand...

Thankfully it's the light (flash was used) that plays trick. You can just about see the head of a inverted torx screw. I think it's the bracket holding the generator?

Click to expand...

Ah yes, all becomes clear now.

Take another picture in a week or two and compare and if not different I would say those are old markings

There's been a development and I now think I know were the stains come from.

The car has been in storage over the winter. After its first drive this year there are a lot more stains and a puddle of green liquid on the under tray. The puddle is located in the area below the water pump and a/c compressor. Engine coolant and washer fluid should be blue. I believe the oil in the a/c compressor can be green in colour? My guess is that the oil is leaking from the compressor shaft seal. Does that make sense?




I've seen small stains on the under tray for about two years, I think. But I haven't been able to figure out were they come from until now.

Last summer felt the a/c system didn't blow cold enough air. During the autumn I therefore had a service done on the a/c system where they tested it for leaks (passed) and refilled refrigerant. With a newly pressurized system and (maybe) dry and hard seals from standing still all winter, the have become worse now when I started to use it again.

I will have workshop that did the service on it last year have a look at it. But I fear that I might need a new a/c compressor which seems rather expensive, at least if you buy it from BMW. Does anyone know what OEM brand BMW used for the a/c compressor on the E86 N52?

A green dye is usually added to the a/c system to help detect leaks. The dye fluoresces under UV light (black light) so if you've got a UV light source you could try that to confirm the source of the leak.

I understand the compressor seals are more likely to leak if the system isn't used regularly.

A late update to this thread.
I had the ac system tested and it was confirmed that the ac compressor was leaking.
The ac compressor had developed, what looks like verdigris, that was visibly pushed out through its joints. The system was drained and the ac compressor was replaced with a new (used) unit, since BMW wanted ridiculous amount of money for a brand new unit.
The dryer/filter was also replaced and the system refilled.