How to Change the Thermostat in a 1999 Eclipse GS

The 1999 Eclipse GS uses a thermostat to control coolant flow in and out of the engine, similar to a bouncer at a nightclub. When the thermostat goes out, it either lets coolant flow too much, which never allows it to cool down in the radiator, or it shuts closed and never lets coolant into the engine. Either way, it can result in an overheated engine, making thermostat replacement necessary.

Instructions

1

Wait for the engine to cool completely, at least four to six hours. Place a drain pan underneath the front edge of the engine. Locate the thermostat housing, which is at the front of the engine and is connected to a downward-facing radiator hose. Unbolt this housing from the engine using the ratchet.

2

Pull the thermostat off of the engine, noting where it is oriented in the housing. Dispose of the old thermostat. Install the replacement O-ring onto the replacement thermostat then install the replacement thermostat into the housing in the same orientation as the original thermostat.

3

Place the thermostat housing onto the thermostat and bolt it in place using the 3/8-inch ratchet and socket. Open the radiator cap. Fill the radiator with a 50/50 mixture of water and anti-freeze until the radiator is topped off.

4

Start the car and turn the heater controls to the "high" position then let the car run for 10 minutes. Turn off the car and let it sit for at least an hour. Open the radiator cap again and top off the radiator with any additional coolant if necessary.