The Toyota Tacoma 2.7 litre engine uses a mechanical thermostat to regulate engine temperature. As the temperature of the coolant rises, the thermostat opens up, allowing more fluid to flow past the cooling fans located in the radiator. This lowers the temperature of the radiator fluid and forces the 2.7 litre engine to run cooler. If the thermostat stops working, the engine could possibly overheat. If the engine overheats, the aluminium engine heads could warp and cause thousands of dollars in damage to the truck's engine.
Drive the Toyota Tacoma onto a set of ramps to lift the front of the vehicle off the ground. Block the rear tire with a wheel chuck for safety.
Remove the radiator cap from the top of the radiator to relieve pressure on the coolant system. Do not remove the cap if the engine is hot. Wait until the engine cools to prevent serious injury from steaming hot coolant mist.
Open the petcock located on the bottom left of the radiator and drain the coolant into a drainage pan. Close the petcock once the fluid drains from the Tacoma.
Trace the lower radiator hose to the location where the hose connects to the water pump. Remove the hose by squeezing the pressure tangs on the radiator clamp together. Pull the hose off the water inlet tube.
Remove the two bolts that secure the inlet tube to the water pump with a 12mm socket. With the bolts removed, the inlet tube easily falls off the water pump. The thermostat, o-ring and gasket are inside of the water inlet tube.
Discard the thermostat, gasket and o-ring. Place the new o-ring inside of the water inlet tube.
Put the spring end of the thermostat into the water pump and then place the gasket around the thermostat. Hold the two in place with your fingers while you adjust the water inlet tube over them.
Secure everything onto the water pump with the two 12mm bolts.
Reconnect the lower radiator hose by sliding the hose onto the inlet tube. Squeeze the pressure tangs on the clamp and slide it approximately 1 inch from the end of the hose and let go of the tangs.
Pour a 50/50 mix of antifreeze, also known as coolant, and distilled water into the radiator.
Start the Tacoma for a period of five minutes with the radiator cap off. This circulates the fluid through the engine and dispels air trapped in the system. Stop the engine, top off the radiator with a 50/50 mix of coolant and distilled water. Place the radiator cap back onto the Tacoma.