Chevrolet Repair: 2000 Malibu, losing coolant, radiator cap

Question
I had purchased a 2000 Malibu with a bad intake gasket.  We fixed that problem, then we started losing coolant, but it was not leaking from the motor.  We replaced the head gaskets and now it is still doing the same thing.  We fill it up with coolant and we can run it all day long like at a idle,  but as soon as we start driving it, it pushes it back into the over flow tank and we lose all of the coolant?  Please help we are out of ideas.

Answer
Hi Jamie,

Thermostat???  If it has been over heated once, it is bad.  Cheap fix if not done already.  

Bad radiator???  Plugged up can cause flow issues, or cooling ability issues.  If the head gasket leaked when you bought it, possibly the prior owner tired BARS LEAK!!!

Collapsing Hose???  Did you use the bleeder fittings on the cooling system???  Radiator cap???  Heater core, same problem as radiator???

Did you use the correct color coolant???  Mixing these colors can cause a gooish, slimy, gel.  Can cause pluggages, as you can imagine.

Usually a load overheat, but idle no trouble, means radiator.  

C J S