The Scheduled Maintenance Guide states that the coolant needs to be replaced. But a chemical flush of the cooling system is an important part of the preventive maintenance necessary to prevent scale buildup in the engine. Several manufacturers offer cleaning agents with detailed instructions on the bottle. Always allow the radiator to cool before removing the cap, as the hot water and/or steam that escapes could cause severe burns. Follow local laws regarding disposal of the used coolant. Many municipalities allow coolant to be flushed down the septic system.
The radiator drain is located on the bottom of the passenger side. Remove the radiator cap, then turn the drain valve counterclockwise to open it, but not so far that it comes out of the threaded portion of the valve. A pair of pliers might be required to loosen the valve, just remember that it is plastic, so be gentle. Having a section of 1/4 or 3/8" hose to go on the hose barb will direct the flow into your drain pan. Once drained, close the valve, and add the cleaner to the radiator. Fill the radiator with distilled water and replace the radiator cap. Start the engine and turn your heater temperature control to maximum heat to allow the cleaner to flow through the entire cooling system. After cleaning, allow the radiator to cool, then drain it. Refill with distilled water and run the engine again to rinse out the system. Repeat rinsing at least one more time to be sure all the cleaner is out of the system. Plan on having about four gallons of distilled water to complete the flushing and filling. I have included these steps so you know what is involved in flushing. Please follow the instructions provided by the manufacturer of the cleaner.
To clean the overflow tank, remove the bolt holding the battery strap, and swing it out of the way. The tank will lift straight up and out. Rinse out the tank with tap water and re-install it. Since you're at the battery, this is a good time to inspect the terminals for corrosion and the caps for any leakage.
Use the red Toyota Long Life Coolant to refill the system, and the overflow tank. Start the engine with the cap off and continue filling while the engine warms up and the thermostat opens, bleeding out any trapped air. Once the thermostat is open, revving up the engine a little will help move any air pockets to the radiator. If the coolant you drained from the system is something other than the red coolant, consult with the dealer to determine which type of coolant should be used to refill your system. The system's capacity is 2 gallons for the I4, 2 1/2 gallons for the V6, and a little more when either one is equipped with the manual transmission. Toyota recommends a 50% mix for protection down to minus 31 degrees F., and 60% coolant for use down to minus 58 degrees.
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