[mrleba18]

I have read a couple of threads regarding a similar issue. None of which seem to give any concrete root cause of the issue.

Coolant is disappearing, no visible leaks, never any smell of coolant, oil appears to be normal/not contaminated.

2012 335i 67K on the engine

The only cooling system related maintenance that has been done was a water-pump at 32K

About a month ago I went on a trip to Colorado, during that time my car was sitting for 4 days.
When i returned I had a low coolant light. It was about 1/2 gallon low.
About 2 weeks later ; same thing, low coolant. Added 1/4 gallon to top it off.
Here we are another two weeks or so later. Added the remaining 1/4 gallon.

Anyone else ever seen this before?

[CTinline-six]

If you are losing coolant, you are either leaking it or burning it.

If you don't have white smoke, and the oil looks fairly normal (no milkshake color) I would pull the bottom plastic cover which would hide any leaks and take a look.

It may only be leaking after the thermostat opens and the coolant circulates more. It could also be a snap lock fitting with a bad o-ring that only leaks a bit when going over bumps.

[Nebo]

I'm about to replace my expansion tank and water pump due to cracks in each....leaking coolant like crazy....