Ard, Maybe not just out of the blue. I didn't notice any problems till it got cold for the first time this season. I am a little concerned also that air could have built up in the system. The last time I had the cooling system opened up was for an over flow tank replacement just over a year ago. I did two cycles of the auto-bleed at that time also... thought I got all the air out then but who knows. Interesting side note, I check my coolant levels on a monthly basis, and never noticed it getting low, the only indication of air was the poor heating and spitting during the bleed cycle. BTW I also did a new pump and T-stat two years ago. I hope the air wasn't left over from that project.

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07, E70 3.0si N52B