In my case the leak was always when the system is pressurized and the coolant was hot. I let my car sit for a few days and never noticed a leak. Most of the coolant loss probably happens while driving or evaporates when hot.

Good luck OP! Keep us updated.

 

good luck, i hope it's just the expansion tank as well

 

99.9% sure I found where it is dripping. I finally got a glimpse of coolant running off of the block and onto the steering rack below the water pump. Still have to get under it and check to be sure.

 

Leak found!

It's a weep hole on the block. To the left (or passenger side) of the waterpump.

Photo from above. Really hard to see.



And from below.

 

Is that the water pump weep hole? Or something more serious?

 

Here's a better photo of my weeping weep hole.



Whould this suggest valley pan gasket/transfer pipe? Or water pump?

 

Most likely coolant transfer pipe. Another possibility is also timing cover to engine block coolant leak, but not as common as coolant transfer pipe.

 

I would really hope not. I just had the timing case covers done not long ago. Just 3 months ago.

 

Update!


I did the transfer pipe and valley pan gasket. Seems to have solved my issue. Only took about 5 hours with a collapsable pipe kit and an extra set of hands.

Now I have a whistling noise at operating temps coming from my expansion tank. So that will be next I guess haha

 

Yeah, the BMWs suffer from a weak coolant system. I don't know if your coolant system was refreshed at the normal 75K-80K mile mark. If so, your mileage suggests you are entering a second wave of issues and will need to look at the cooling system top to bottom again. If these are the first time issues for a 160K mile car consider yourself lucky you made it this far. Prime candidates will be the water pump, thermostat and vent tube in addition to your expansion tank, and of course hoses.