The 1998 Honda Civic uses a mechanically operated thermostat to regulate engine temperatures. As the fluid flowing through the engine heats, it causes a spring inside of the Civic's thermostat to compress. Once compressed, more fluid flows through the engine. This results in a reduction in the coolant temperature. When the thermostat malfunctions, the spring fails to compress and the engine ultimately overheats. When this happens, your must replace the thermostat in your 1998 Honda Civic.
Drive the Honda Civic onto a set of ramps and secure the parking brake. Raising the front of the Civic allows more room to work under the engine.
Place a drain pan under the petcock located on the bottom of the radiator. Open the petcock by placing a 1/4-inch ratchet driver onto the petcock and turning it counterclockwise. Drain the coolant into the plan. Close the petcock once all of the fluid drains from the radiator.
Follow the lower radiator hose from the bottom of the radiator to the point where the hose connects to your Civic's engine. The hose connects to a small metal housing, which holds the thermostat inside the engine block.
Remove the radiator hose from the thermostat housing by squeezing the two metal tabs together with a pair of pliers. This releases the clamp's pressure on the radiator hose. With the pressure released, pull the hose off the housing.
Remove the two bolts that secure the thermostat housing to the lower block by using a ratchet and 12mm socket.
Pull the thermostat housing off the lower engine block. The thermostat and thermostat gasket come off with the housing. Remove the used thermostat and gasket.
Scrape the bottom of the thermostat housing and the mating surface of the Civic's engine block with a wire brush or metal scraper until both are clean.
Place the spring end of the new thermostat inside the engine block, and hold it there with one hand.
Place the thermostat gasket over the thermostat, and hold both in place with your hand.
Place the thermostat housing over the gasket and thermostat, and secure it with both 10mm bolts.
Slide the radiator hose back onto the thermostat housing, and secure it with the radiator hose clamp.
Remove the radiator filler cap located on top of the radiator. Pour the coolant back into the radiator. Put the radiator cap back on.
