[Cartman]

it sounds like its just steam escaping into your overflow bottle. when hot, the overflow bottle will be a little overfull as the steam has forced some coolant out of the system. when the system cools, itll draw the coolant back in. you could have a small airpocket in your cooling system. check your level when its cold, add up tot he cold line. it should burp itself.if not, there is a bleeder screw located under your filler neck, this can be utilized to bleed air from the system. i only suggest the bleeder when the system is relatively cool though.