b48 coolant loss

[O183618]

my b48 is losing a lot of coolant, and the bulk of it seems to be leaking out the back of the engine, more so on the drivers side (rhd). I originally suspected (before discovering this drip) water pump failure but this doesn’t seem to be the case anymore. There is moisture underneath the water pump area, but it’s nowhere near the visible leak and can’t see any fluid coming out of it when running.
Only losing coolant when hot and under pressure, no oil contamination, and only from the main reservoir.
Anyone had anything similar?
Luckily i’ve got the car booked in for some maintenance next week so the garage will have a look while it’s in, just want to track the issue to save time.
Any words of wisdom appreciated, will attach a photo bellow, which was taken just a bit behind the front right wheel. Tia

[Uncle boshy]

we had this issue last year on our B48 - had the symptom of coolant needing topping up, but no obvious leak and then it spat out all the coolant on the road, luckily the mrs was able to pull over quickly and no harm done.

in our case it was the plastic vent line between the cycling head and expansion tank, a well known issue. All it, including refilling etc it was £180 at our local indy.

but you can do it yourself quite easily

try about 6 messages below the headline

https://f30.bimmerpost.com/forums/showthread.php?t...