1999 Chrysler Sebring 6 Cyl overheating.

I've had the same thing happen to a few of my cars a few times... It means there is a small loss of vacuum somewhere (probably also equates to a loss of pressure too, its just so minute that you can't feel it). Could be a pin hole, corrosion around the hose nipples, water pump seal or gasket ect... Run a pressure test with the car off and listen for small leaks. When the coolant cools down and contracts, instead of sucking coolant from the reservoir, it will just suck coolant in through the small hole in your system. You may not see coolant come out because the leak might be SO small that only a little coolant (which is much thicker than air) is able to get through and evaporates before it even leaks onto the ground.

The best way to quickly and easily breathe your radiator is take the cap off, cover the opening with the palm of your hand and massage the upper hose. You will hear air bubbling out of it and down the drain hose and out the reservoir... When you release the hose, coolant will rush in from the reservoir.

if i massage the hose like you metioned in the second post, does the care need to running? the hose is pretty stiff.

if i have one hand on radiator opening to block the air, whats the difference then if i massage the hose with the cap on? relaease the hose? your mean stop massaging it?

The hose will only be stiff when the engine is hot because the pressure builds... When the car is completely cold, or cool, remove the radiator cap, put the palm of your hand over the opening, and squeeze the hose until you hear gurgling, then release... keep doing that until you feel there is now coolant in the upper hose... Now return the radiator cap and you should have removed most of the air from the cooling system.