Originally Posted by stoney 81ta
HI all picked up a 07 grand prix for a new driver,first thing the car still has warranty,but i want to have a idea when i take it back to dealer.Noticed that the coolant overflw bottle was low on dexcool,bought some and added to the coolant fill bottle to the cold fill line,now it seems that the level has drop about a litre of coolant.Is this normal for these new cars and heard some issues about dexcool.Any help and advise is appreaticated.Thanks all.
The cooling system puts hot expanded coolant into the catch bottle when the quantity inside the cooling system, due to thermal expansion, forces the relief valve in the pressure cap open. When the engine is shut off and cools the coolant inside the cooling system contracts forming a vacuum which then draws the excess that had been deposited in the overflow tank back into the radiator/cooling system.
If you've added coolant to the overflow tank bringing the level to the cold line. The heated operating engine should have added some quantity to that. This quantity basically just shifts back and forth, being deposited in the tank when hot and drawn back into the cooling system when cold.
If the amount you added is also being drawn into the cooling system when the engine cools, it's an indication that the system either wasn't filled to capacity when new; or the system is leaking/loosing coolant somewhere which is being made up with the cool-down quantity sitting in the catch tank.
Of course some amount in the catch tank is lost to evaporation, but this should be pretty minimal. The catch tank should go for long periods, weeks to months, without needing additional coolant to maintain proper reserve levels.
Dexcool is very sensitive to air in the system, this results in a chemical breakdown of the Dexcool when its hot, making quite a mess in the cooling system. You need to keep a careful eye on this condition to insure that a situation doesn't develop where a total loss of reserve tank coolant quantity would allow the cooling system to suck air into itself rather than Dexcool.