The cooling system in your Toyota Corolla uses a mixture of distilled water and coolant to drop the temperature in the engine. The system is regulated by the thermostat, water pump and radiator. The coolant will pick up sediment and rust from the engine; it should be drained and refilled occasionally for optimum effectiveness. In this case, the project vehicle is a 2001 Toyota Corolla, but the process is similar for other vehicles as well.
Place a drain bucket underneath the bottom of the radiator. Locate the draincock, a white plastic knob located at the bottom of the radiator. Turn it counter-clockwise to open it up and allow the coolant to empty from the radiator. Once it's empty, reinstall the draincock.
Loosen hose clamp that secures the lower radiator hose to the radiator using the flathead screwdriver and pull the line off of the radiator to allow it to drain into the bucket. Once the coolant is drained, reinstall the line using the flathead screwdriver.
Open the radiator cap on top of the radiator and fill the radiator with the Toyota pre-mixed coolant. Reinstall the cap and allow the engine to run for 10 to 20 minutes with the climate control set to high heat.
Turn off the car and allow it to cool down for 20 minutes. Open the radiator cap again and top off the radiator with additional coolant.
Reinstall the radiator cap and open the cap on the coolant overflow reservoir. Fill it with coolant until it reaches the black fill line marked on the side of the reservoir.
By using pre-mixed coolant, you will avoid having to mix coolant and distilled water 50/50 as was done in the past. If you can't find pre-mixed coolant, get distilled water as well. Mix the two together in a 50/50 ratio when you pour it into the radiator.
Allow your engine to cool before you start to work on the cooling system, otherwise you risk burning yourself.