In order to keep a Toyota Highlander in top working condition, an owner must perform regularly scheduled maintenance. You can hire a mechanic to complete these tasks, but some, such as a radiator flush, are easy enough that anyone can do it. If you neglect this maintenance, the debris in the radiator can damage the coolant system.
Park the Toyota Highlander on a level surface and set the parking brake. Next, pop the hood and check the external temperature of the radiator. If it is cool to the touch, then proceed. If not, wait until it cools off before you continue.
Turn the radiator cap one revolution, take a few steps back, wait a minute or so and then completely remove the radiator cap. The pause allows the internal pressure from the radiator can to subside; otherwise, the hot coolant can erupt and severely burn anyone in the area.
Place a bucket with a 2-gallon capacity underneath the radiator and directly below the drain plug. The drain plug is usually on the passenger's side bottom corner of the radiator in a Toyota Highlander.
Open the radiator drain plug and allow the old coolant to drain completely into the bucket. Upon completion, pour the coolant into a sealable container for proper disposal. Be careful with the old coolant as it is very toxic to people and pets.
Shut the drain plug and fill the radiator with distilled water. Then, open the drain plug and allow the water to flow into the bucket. Repeat this process until the water runs debris free out the bottom of the Toyota Highlander's radiator. You can use tap water from a garden hose, but ordinary water may leave sediments behind that will damage the coolant system.
Close the drain plug and dispose of the radiator flush properly.
Pour fresh coolant into the radiator. Fill it within an inch of overflowing from the top of the radiator. The recommended coolant for the Toyota Highlander is Toyota Super Long Life Pink premixed coolant. You will need 2 or 3 gallons depending on the size of the engine.
Start the engine of the Toyota Highlander and allow it to run until the cooling fan turns on twice. Then, turn the engine off and check the coolant level. If it is lower than required, add more coolant. Otherwise, put the radiator cap back on and close the hood.
