Q: How to check and replace a malfunctioning thermostat?
A: If you suspect a faulty thermostat, test it out before you replace it. To test, submerge it in water heated to its rated temperature (typically 195°F). The valve should fully open at this temperature. As the water cools to about 10 degrees below this (around 185°F), the valve should close completely.
Q: How to remove and install the thermostat housing and Thermostat for Pontiac Fiero?
A: The thermostat housing is on the upper end of both the 2.5L four-cylinder and 2.8L V6 engines. To remove, twist the thermostat housing cap clockwise, then pull out the thermostat. Clean the housing and lubricate the O-ring with white grease. If replacing the housing or gasket, disconnect the radiator hose (expect some coolant spillage). Disconnect the coolant temperature sensor wire. If replacing the housing, remove the sensor with caution. Remove old gasket residue from the cylinder head. Check the housing for external damage or internal corrosion. Apply RTV sealant to the new gasket and position it. Install the housing, tightening bolts securely. Wrap the sensor threads with Teflon tape, reattach it, and reconnect its wire. Refill with coolant, install the thermostat and its cap. Start the engine and check for leaks.