Car running hot?

SOURCE: 2000 Malibu keeps running hot.

You replaced the head gasket but did you get the head or heads checked for cracks or check the block for warpage?

SOURCE: heater not heating hot enough. heater core not

Good place to start is a cooling system flush and thermostat replaced.

SOURCE: heater core seems fin no leaks or smells but does

More than likely your core is clogged, generally you have already tested it by warming up the engine and feeling both hoses confirming the flow is not getting to the return. Some people have had success by removing the hoses @ the engine and using a garden hose, flush the lines in both directions (as i mention garden hose, note that the pressure is not great, other methods with more pressure could cause a core failure). You could always bring it to a shop and have them complete a flush service with a mention of the hc clogged as well. You will have to refill your coolant in the radiator and work out any air afterwards.

SOURCE: My heater in my 1996 VW Cabrio will not get hot

sounds like you might have an air lock in the system,try "burping" the system by removing the radiator when the car is cold(had not been started for a couple of hours),then start the car and let it run with the defrost only, on full blast until the car reaches normal operating temperature this will allow any air in the system to escape and this will also cause a little coolant to spill out.When you go to refill the coolant do it when the car is cold if you put cold coolant in a hot engine it tends to case problems with seals and gaskets mainly but can also cause problems for the radiator and related parts,I really hope this helps good luck

SOURCE: I have a 1997 Chevy Malibu that is over-heating.

if you do not turn the a/c on, do the fans cycle? turning on the a/c will signal fan demand - this indicates the the fan and circuits are OK. if the fan cycles with the a/c off, we can move away from a fan issue. if not, look into that. have you tested the rad cap? i believe this model has one cap on the expansion tank and no rad cap, if i remember correctly. i have actually run into one of these cars where an incorrect cap was installed, causing similar symptoms. it sounds as if you know what you are doing, but is there any possibility that there is an air lock in the cooling system? if there is heat coming out of the vents when the car is hot, there is probably no issue there, and also likely means the waterpump is ok. let me know and we'll talk later if necessary, good luck!