Pretty common problem. It CAN be a BHG but more than likely you just need to burp your cooling system. Here's a link from Suprra Girl
http://www.toyota-supra.info/forums/...ead.php?t=3029
Also mrnickleye suggested once, and I can't remember where I just know it was him, to cut the dangley thing on your thermostat and bore the hole out to 4mm to help reduce this problem in the future.