I’m posting in both E46 and E83 forums, since they’re similar for this problem. I have a 2006 X3 (3.0i M54) with about 175K on it. The upper radiator hose popped off the radiator neck, which includes the smaller expansion tank neck. I was able to re-install it since nothing appeared broken. After topping up and bleeding the air out, it seems to be holding. After a few drives, I ran some lockwire around the hose fitting and secured it as a safeguard, but why would this happen? I read some other posts about possible head gasket leakage over pressurizing the system. It’s winter in Maryland, so ambient temperature is lower than usual.
Before this happened, I had just pulled a fault code for the thermostat, and reset it to see if it came back, which it did not (but probably will). I got a low coolant light so I had topped up the coolant keeping the float gage at its proper height. The hose popped off about the third time we drove it, after this topping off.
About two years ago, the expansion tank blew out, but I assumed that was due to age as it’s common on older BMWs. I noticed that when the upper hose came off, and the engine began to get hot, I wasn’t seeing any low coolant light. Weird. Pretty sure I never overheated the engine, but can’t say for sure. Engine currently runs great and I’ve seen no signs of oil or coolant mixing.
Probably the worst Bimmer I’ve owned, with the X-drive triad of lights, cooling issues, replacing the transmission, oil leaks and a bunch of other things. Has never stranded me, but the cooling system has me nervous. TIA
It appears that the primary issues I've had are the use of Plastic Cooling Components. Sooner or later they will fatigue and break and the recommendation is around 100,000 miles. I just replaced my upper hose $45.00 and the Expansion Tank $135.00 from BMW. Previously did the Thermostat with new cover. The primary oil leaks seem to be the Valve Cover, the Oil Filter to Engine Block connection and possibly the oil pan.
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