How do I Replace My Thermal Relay & Thermostat?

The thermal relay sensor and the thermostat are very important components in the engine's cooling system. The thermal relay sensor is designed to operate the cooling fan when the coolant temperature reaches a certain temperature. The thermostat is designed to open and close according to the temperature of the engine coolant. Once the coolant temperature gets too high, the thermal relay sensor sends power to the cooling fan, enabling it to cool the engine. The thermostat opens when the coolant temperature gets too high and allows the coolant to circulate throughout the engine.

Instructions

Park the vehicle in a safe work location that has a flat surface and turn the engine off. Engage the parking brake and open the hood. Wait at least a couple of hours for the engine to completely cool down.

Check the temperature of the radiator cap once the engine has completely cooled off. Slowly unscrew the radiator cap and place it in a safe area.

Slide under the front of the vehicle and place the drip pan underneath the coolant drain plug on the bottom of the radiator. Loosen the drain plug and wait for all of the coolant to drain out of the radiator and the engine block. Re-tighten the drain plug.

Locate the thermal relay sensor. The round thermal relay sensor will be located at the head of the upper or lower radiator hoses. The thermal relay sensor on some vehicles is screwed into the radiator. The thermal relay sensor will have wires coming out of the end of it that send the temperature information to the cooling fan switch. Pull the wires off of the front of the sensor.

Unscrew the thermal relay sensor with an open end wrench by positioning the end of the wrench on the back side of the sensor. Turn the wrench counterclockwise to loosen the sensor. Once the relay sensor is loose, finish unscrewing it with your hand. Push the wires onto the front of the new sensor.

Wrap the Teflon tape around the threads of the new thermal relay sensor from left to right. This will prevent the tape from unraveling when screwing the relay sensor back into the head of the radiator hose. Screw the new thermal relay sensor in tight with your hand. Tighten the relay sensor with the open end wrench until the sensor is tight.

Follow the top radiator hose from the radiator to the thermostat housing port. Unscrew the hose clamp from the hose that is secured to the port with a flat head screwdriver. Pull the clamp back onto the hose with your hand. Twist and pull out on the hose at the same time to remove the radiator hose from the thermostat housing tube.

Unscrew the two thermostat housing mounting bolts on top of the thermostat housing with a ratchet and socket. Pull the bolts out and place them in a safe area. Pull the housing off and place it in a safe area. Pull the old thermostat out of the engine block and discard it. Install the new thermostat into the engine block with the thermostat spring facing inside the engine block. Scrape away any excess gasket from the base of the thermostat housing and the base of the engine block. Wipe away the excess gasket with a clean rag.

Apply a thin bead of the red high temperature silicone around the base of the thermostat housing. Apply the gasket onto the silicone with the holes of the gasket matching up with the holes on the thermostat housing. Lower the thermostat housing over the new thermostat and onto the engine block. Screw the two mounting bolts back into the housing and tighten with the ratchet and socket.

Push the radiator hose back onto the thermostat housing port and secure the hose clamp over the radiator hose and the thermostat housing port with the flat head screwdriver. Fill the radiator up with antifreeze and water until the fluid level stabilizes at the top of the radiator. Crank the engine and wait for the engine to reach operating temperature. Once the engine reaches its operating temperature, the thermostat will open and allow the coolant into the engine block. This will also cause the fluid level to drop inside of the radiator.

Continue adding antifreeze and water to the radiator with the engine running until the fluid level stabilizes at the top of the radiator and does not drop. During the time that the thermostat opens, the cooling fan should also come on. Screw the radiator cap back on and inspect the thermostat housing for leaks and check the thermal relay sensor for leaks. Turn the engine off and remove the drip pan from under the vehicle.