wouldnt a sticky thermostat cause over heating issues? on all my bmw's it did. even if it stuck open if the car idled for a long time it would get warmer and warmer and the temp couldnt come down.

 

when the car is cold the overflow tank should be at the high mark or the low mark? i figured the high but the past 2 days i have had to fill it from exactly the low mark to the high mark. am i just over filling the over flow?

 

When a cooling system is fully caped it is esentially a closed system. The overflow bottle is a intrigal part of the system. The radiator cap serves a few functions. When the engine heats the coolant expands. Once it reaches the pressure of the radiator cap, all excess coolant will go to the overflow bottle. When the engine cools the coolant shrinks drawing the overflow back into the cooling system. Once the coolant line and overflow are depleted the cooling system will only draw air back into the system as the engine cools. Therefore, in this case the cooling system gets low. On vehicles with a radiator cap and an overflow bottle cap you have to first fill a cool radiator and then fill the overflow to the proper level.

 

It could also be the ac/heat control going out as well..I know these are known for having this issue as well so you may want to check that.