My wife have a Cooper S Countryman, year 2013. 22000 km on the clock.
She has had it for 9 month, bought from BMW in Germany.
Last week end we were passing some mountains in snow, wet snow ,wind and the front got some covered by ice/snow. While stopping in a queue I noticed light steam ( clouds) front side, left. I thought it was ice /snow hitting heated surface and meltding. Soon after the heating compartment stopped heating,,,only rather cold air came out. We stoppded, checked the coolant and found it missing some + air bobles in the system.
I also smelled coolant/ antifreeze,, so obviously there was some steaming out!
Until then we had between 0 to minus 10 C on the trip,,,and only minus 2-3 C when it happen..
Filled it up, started up, filled it up agian,,,and after a while the heating came back. I stopped every now and then to control the level, but things were all right,,just some air bobles in the begining , but soon everything got stabile.
Now, 600 km and 3 days later, everything is still fine and I never had to top the coolant. We have also during those 600 km been trough everything from + 5 C to -30 C !
There is no temperature gauge here, but a warning sign only when temperature is too high. That never came on!
So, what happen?
I expected it to be a leak, but obviously it was not!
Is there an air outlet on the expanding tank that might have been blocket by ice?
Was it too little coolant in the first place? ( I haven't checked for a while before this)
Is it any valve or thermostate that played us a trick?
( we'll have it to service soon anyway, but I am just curious, It's still warranty on the car