Help! Location of thermostat

Can anyone help me? I need to change the thermostat in my daughter's 1998 Grand Prix. When she's driving, the temp almost goes into the red zone, then it backs way down to almost nothing, all within a minute or two. This keeps happening the whole time she's driving. At the same time, when she tries to run the heater, when the car temp is higher (above 190 or so), the heater only blows cold air. I figure the thermostat is sticking and is causing both problems,but I'm not sure where it is to change it. Can anyone tell me where the thermostat is located? I appreciate any help.

Da.. what engine?

It's at the end of the top radiator hose towards the motor CLICK HERE (http://macgp.clubgp.com/howto/engine/tstat/tstat.htm) for instructions.

~Larry~

I was always told, "follow your top radiator hose. It's at the end".
http://img.photobucket.com/albums/v425/kustomkid54/1998PontiacGrandPrixGTP004.jpg

I have been experiencing exactly the same issue you described on your daughter's Grand Prix. I replaced the T-Stat and it got worse...I took it to a repair shop and they indicated the problem had to do with leaks in the Intake Manifold...they took it apart and replaced the upper and lower gaskets on the plenum...nothing has seemed to correct the problem....I would be very interested to know if anyone else has successfull corrected this problem....Thanks, Redgrandprix.