Drove my 2006 z4 3.0 to work noticed I didn't have any heat . Temp gage straight up. Trip of about 15 minutes. Stopped for about 5 minutes and drove about half a mile when temp gauge shot up. Turned around and parked it for the day. Drove home that evening and same sequence. Never ran hot but about 1 minute each way.no check engine or low coolant warning.