If your 1998 Ford Escort has not been warming up properly, it's most likely due to sludge buildup around the mechanical thermostat. The sludge causes the thermostat to fail in a "safe" position; in other words, it will fail in the open position, letting fluid flow freely through the engine. This prevents the engine from heating properly. Although this is better then overheating, it can get rather cold inside the car during the winter.
Locate the thermostat housing by tracing the radiator hose to the location on the the intake manifold where it connects. The component the hose connects to is the thermostat housing.
Remove the radiator hose from the housing by loosening the band clamp that holds the hose onto the housing. Push the clamp farther onto the hose to prevent losing it while changing the thermostat. Pull the hose off of the housing and push it off to the side. Plug the hole in the radiator hose with a shop towel to prevent fluid from leaking onto the engine.
Remove the two bolts that hold the thermostat housing to the intake manifold of the Escort. These bolts will be used again so they should not be discarded. Once the bolts are removed, the thermostat housing can be lifted off of the intake manifold.
Remove the old paper gasket that was sandwiched between the housing and the manifold. Pull the old thermostat out of the intake. The thermostat sits on a machined lip inside of the intake and is not bolted into place.
Place RTV gasket maker on the machined surface of the intake manifold where the old gasket was. Allow 5 minutes for the RTV gasket maker to "skin" over or firm up.
Place the new thermostat into the intake manifold. Pay attention to the top end. This end must protrude from the intake manifold or the thermostat will not work properly.
Place the thermostat housing onto the intake manifold and bolt it back into place using the old bolts. You'll notice some RTV gasket maker squeeze out. This is normal and should not be removed. It will assist in the sealing process.
Pull the shop towel out of the radiator hose and reconnect it to the housing with the band clamp. The clamp should be very tight to prevent leaking.
