Thermostat Installation in a 1985 MR2

Like many vehicles, the Toyota MR2 has a water-cooled engine in which the coolant temperature is regulated by a thermostat. Unlike most vehicles, the MR2 has a rear-mounted engine and a radiator at the front of the car. Although in theory the cooling system and thermostat work the same, the procedure to replace a faulty thermostat and bleed the cooling system afterwards is a bit different than the process to repair a more conventional front-engine vehicle.

Instructions

1

Remove the pressure cap from the coolant fill location in the engine compartment at the rear of the car. Place a clean drain pan under the white plastic drain valve near the bottom of the radiator at the front of the car. Twist the valve with a pair of pliers in a counterclockwise direction. Allow the coolant to drain into the pan. Close the drain valve and remove the drain pan from under the car.

2

Follow the bottom radiator hose to the water inlet housing mounted in the trunk compartment. Squeeze the tabs on the hose clamp at the housing with a pair of pliers. Slide the clamp along the hose a few inches and release the tabs. Loosen the hose from the water inlet on the housing by twisting it back and forth by hand. Pull the hose straight of the water inlet and push it to the side.

3

Remove the two retaining bolts from the water inlet with a wrench. Pull the inlet away from the water inlet housing. Pry the inlet away from the housing carefully with a flat blade screwdriver if it will not come off by hand. Avoid scratching or gouging the mating surfaces of the inlet and the housing with the edges of the screwdriver, as a leak can form.

4

Remove the water inlet gasket from the backside of the inlet. Pull the thermostat out of the water inlet housing. Clean any gasket residue from the mounting surfaces of the water inlet and the inlet housing with a rag. Push a new water inlet gasket onto the backside of the inlet.

5

Insert a new thermostat into the mounting hole in the water inlet housing with the spring facing inward. Position the water inlet over the housing and align the mounting holes. Replace and tighten the water inlet retaining bolts. Push the lower radiator hose back onto the water inlet until it is fully seated. Squeeze together the tabs on the hose clamp with pliers and slide it into its original position on the hose. Release the tabs.

6

Push a three foot length of clear tubing over the coolant bleed valve near the driver side of the radiator. Push a like length of tubing over the bleeder valve near the heater core located on the firewall. Hang the opposite ends of each of the lengths of tubing with a piece of wire so that they are higher than the coolant filler opening at the rear of the car.

7

Open the bleeder valves three turns by twisting the knob on each valve. Place a funnel into the coolant filler opening in the engine compartment. Pour the coolant from the drain pan into the funnel until it can be seen in the clear hoses hung at the front of the car.

8

Remove the funnel and twist the cap onto the coolant fill opening one click. Start the engine and allow it to reach operating temperature with the heater adjusted to maximum temperature. Turn the engine off.

9

Remove the cap and add more coolant to the coolant fill opening in the engine compartment. Repeat as many times as necessary until the air bubbles have been expelled. Close the bleeder valves and remove the plastic tubing. Fill the coolant reservoir tank to the full mark with coolant.