2005 Pontiac grand prix replaced the water pump and still heating up
Did you put a new thermostat in?
If steam is coming from underneath the water pump you do not have a good seal. Will have to remove and reseal pump.
Overheating is quite likely the result of air trapped in the cooling system which hinders the proper flow of coolant. You need to get the air bled out of the system and fill it properly for it to work. Could the steam simply be spilled coolant evaporating off a hot engine? Try to determine if you have an actual leak somewhere and where it is coming from. The plastic elbows that take coolant to the heater are also prone to failure and should be replaced whether they are leaking or not because if they're not leaking now they eventually will be. And yes, if the water pump is not sealed properly you will have to take it off again, clean the gasket surfaces properly and reseal it.
Looking for a Used Grand Prix in your area?
CarGurus has 3,754 nationwide Grand Prix listings starting at $1,195.
Search Pontiac Grand Prix Questions
Pontiac Grand Prix Experts