1999 Pontiac Grand Prix Thermostat

MRHAGGIS

MEMBER
1999 PONTIAC GRAND PRIX
6 CYL
FWD
AUTOMATIC
140,000 MILES

I would like to replace the thermostat to see if that corrects a problem with really poor heating (meaning not much heat). Fluid levels are optimum, the hoses are relatively new and sound, the radiator is a little bit cruddy inside. The car is in excellent condition and running order otherwise.

What seems to be the location of the thermostat is on the side of the engine and is buried under all manner of parts, cables, covers, pipes, wiring, hoses, and so on. I can just see it with a trouble light and some effort. There is, however, another housing which also somewhat resembles a typical thermostat housing, located higher up at back of the engine.

My experience with changing thermostats is limited to Olds and Ford, they were quickly accomplished. This seems like it might take somewhat more work - if I can identify which is the right housing! IS there a particular sequence of removal for all the parts to get at the thermostat?

Thanks!

1 Reply

MERLIN2021

MECHANIC
17,250 POSTS

Follow the upper radiator hose, goes right to it.
Try warming the Vehicle, then carefully feel the heater hoses, are they both hot? If one is cooler than the other, You need to flush the core, or do a replacement job on the heater core. Also if the system has a heat control valve on the heater hose, make sure it is working! Also check the thermostat, and the temperature blend door, thats under the dash, in the heater plenum. You can flush this yourself, buy the prestone flush kit and install the tee in the heater return line. Disconnect the heater hose at the waterpump, clamp the hose in back of the tee you installed and back flush till it runs clear.20 mins or so. Where you say the radiator is cruddy inside, I would get a flush kit and some fast flush, follow the directions, and do a good flush of the entire cooling system.