1998 Oldsmobile Intrigue Cassondra

That's not much to go on. First check the coolant level. If it's low, it won't circulate hot coolant to the radiator which will cause overheating, and it won't circulate hot coolant to the heater core, so you'll get unheated air in the car. The clue is to feel the upper radiator hose when overheating is indicated by the dash gauge. If it is cold, coolant isn't circulating.

If you installed a new thermostat, on some engines you have to burp the air pocket under it. There may be a bleeder screw on the thermostat housing, or you can unscrew a sensor near it. Thermostats don't open in response to hot air. They have to be hit with hot liquid. If that air isn't bled out, the thermostat won't open so the engine will overheat, although normally that hot coolant will still flow to the heater core and you'll get real hot air, not cold like you're getting.

I'm not sure if that's really a do-it-yourselfer project, plus, I'd want to know how someone came to that conclusion that a new water pump is needed. If you're sure you want to tackle this, get a copy of the manufacturer's service manual, then read through the pages of instructions. You can also get the information online by clicking on "Manuals" under the "Repair and Service" tab at the top of this page.

I'm up against a dying laptop battery so I have to be quick. It sounds more like you have a leaking cylinder head gasket. There's a fast and easy chemical test for that.

We have to discuss this battery issue further. GM has had a real lot of problems with their redesigned generators starting with 1987 models. If yours is defective, to prevent numerous repeat failures, replace the battery at the same time unless it's less than about two years old.