1998 Pontiac Sunfire themostat

Trace the upper radiator hose to engine to find thermostat housing

REPLACEMENT

2.2L OHV Engines

Drain coolant (about 1 gallon) from the radiator until its below the thermostat housing
Disconnect the radiator hose from the thermostat cover
Remove the bolts and lift the cover off you may have to tap the cover with a soft-face hammer to loosen it
Note how its installed then remove the thermostat

2.3L and 2.4L OHC Engines

Drain the coolant from the radiator
Remove the exhaust manifold heat shield
Remove the cover that protects the outlet pipe on the thermostat housing by accessing cover bolts through the exhaust manifold runners
Raise and secure the car on jackstands
Disconnect the radiator hose from the metal outlet pipe
Remove the outlet pipe bolt and carefully separate the outlet pipe from the thermostat housing and the engine block
Note how its installed then remove the thermostat from the outlet pipe