The thermostat on your Honda Civic is an effective component of the cooling system. However, once its thermal mechanism fails and stops regulating engine temperature, it needs to be replaced to prevent engine overheating or under-temperature operation. You can install a new thermostat with a few common tools.
Place a drain pan under the radiator drain valve and remove the radiator cap.
Open the radiator drain valve and remove at least 2 quarts of coolant. Close the drain valve.
Raise the front of the vehicle using a floor jack and safely support it on two jack stands.
Remove the splash shield from the underside of the engine with a wrench or ratchet and socket.
Disconnect the lower radiator hose at the thermostat housing on the engine side. Use a Phillips screwdriver, rib joint pliers or ratchet and socket, depending on clamp type used on your particular Honda Civic.
Unscrew the three thermostat housing mounting bolts with a ratchet and socket.
Remove the thermostat housing, thermostat unit and O-ring or rubber seal.
Set the new thermostat in place along with a new O-ring or rubber seal.
Install the thermostat housing and start the three mounting bolts by hand to avoid damaging the threads. Tighten the mounting bolts.
Connect the lower radiator hose to the thermostat housing and tighten the clamp.
Re-install the splash shield to the underside of the engine.
Refill the cooling system with a solution of 50 percent water and 50 percent antifreeze.
Replace the radiator cap. If your Honda Civic came equipped with a bleeding screw or valve on the thermostat housing, bleed the cooling system.
Start the engine and let it idle for three minutes.
Loosen the bleed screw on the thermostat housing with a wrench or ratchet and socket, just enough to let the air bleed through.
Tighten the bleed screw when the coolant begins to leak through the bleed screw.
Turn the engine off.
Wait about 15 minutes to let the engine cool down and add coolant to the reservoir tank. Make sure the level reaches between the "Low" and "Full" marks.
