Has this ever happend to your car???
2006 330I 88K. iI noticed a coolant leak under my expantion tank. I assumed it was cracked so I replaced. A couple days later more coolant uner tank. Low coolant light would not go off because Thermostat failed in closed position. I could not get radiator to fill. I ran the bleed process 5 times 12 min each. I replaced thermostat and was able to fill radiator with coolant and distilled water. Ran great for a couple of days. Cold morning Sunday and I went outside to warm up car let idle for 10 min. no heat. I proceeded down street to warm engine and yellow engine temp light flashed. Returned home checked coolant and had coolant under expantion tank again. Thermostat failed to open again and engine overheated blowing coolant out bypass in expantion tank. I cycled the key switch cranked engine and noticed the thermostat opened and was operating fine. Filled with coolant. Let sit overnight . Cranked this am, let warm about 15 min. No heat. Cycled key switch and recranked thermostat opened and operated fine. Drove car 70 miles operated fine no coolant leaks.
My question is What sensor operates the thermostat? I am pretty sure that is my problem. Anyone have any similar issues?