2006 Pontiac Grand Prix (6 cylinder, not supercharged)overheating

Your water pump went south. And you need a radiator.

Check the exhaust for white smoke, and check the oil to see if it is getting over full. May be a head gasket.

Just curious, the water pump has metal vanes, not a rubber impeller, and is not leaking. How would the pump go bad, vane broke from shaft?

Yes, but the impeller and shaft are 2 parts--- it is possible that it separated---

Thanks for the help. Will be changing the water pump and radiator.

I wish I would have changed the water pump when I had the heads off... I left it because it is only 8 months old.

Sounds like the water-pump was not you problem, never the less the engine overheated and now you have a bad head gasket or a cracked head.

Definitely the Radiator. Sounds stupid, but first check to make sure the Radiator Cap is airtight. Alot of times when you're able to squeeze your hoses, you might have to change them. There's just 2 going to the Radiator. Top & Bottom.check that the Overflow Tank isn't cracked. If you check all of that and still leaking, you're going to have to get a new Radiator.

One other possibility is if you did not purge the cooling system from the air pockets when refilling with coolant. Also make sure the fans are working properly.

Just to be clear, after motor overheated, the cylinder heads, head gaskets, intake gaskets and thermo stat were changed. The motor is still getting hot, but I am watching it and stopping before it overheats. It has not gone in the red since heads have been changed, It is not being driven, it is sitting while I troubleshoot. I do run it to test things and can see it getting hot, then stop. I hope the cylinder head/gaskets are not bad again. That back head is not a fun swap...

Rowefast has an excellent point-- did you burp the coolant system when you changed the heads??

I had drained the entire system, radiator and block. I refilled it, not sure how to burp it. I ran it, it consumed what I had initially put it, I continued to add until it did not take any more. How do you burp it?

I did open the bleeder on top of the Thermostat housing and let air out until it was just fluid coming out.

What side is the coolant reservoir on? Lift that side of the car with a jack, open the reservior and let the car idle. As it is running squeeze the upper radiator pipe untill all of the air has escaped from the coolant system