I searched around but could not find exactly the information i am looking for. On my overflow bottle i marked off my hot and cold temperature marks. It has been pretty consistent when hot it is at the hot mark and when cold at the cold mark. however i have noticed twice now i will be driving down the road and all of a sudden i loose heat in the car, even with the temperature all the way up. after parking the car and letting it cool down, the overflow level is way above the hot mark. but then i will drive around for the next couple of weeks with no issues and the level goes back to the proper levels. Then again the other night i lost heat in the car and sure enough the overflow is really high. Anyone have any ideas what could be happening.