Plastic radiator overflow tanks or expansion tanks hold extra antifreeze to supply the radiator with in the event of small leaks. Adding too much antifreeze to a radiator or expansion tank builds pressure that can crack the tank. After several years of use, a plastic tanks needs replacement due to the plastic drying and cracking, letting the antifreeze drain out of the bottom. Replace expansion tanks that have small cracks, holes or a lid that does not close securely to forego expensive repairs on an overheating engine.
Turn the vehicle off, open the hood and let it cool completely.
Locate the plastic radiator tank. Follow the small hose near the radiator neck on the fill area. Follow the path of the small hose to the radiator tank.
Place a screwdriver in the hose clamp on the top radiator tank hose. Turn the screw counterclockwise to loosen and pull the hose off. Place a drain pan under the bottom of the vehicle under the tank's bottom hose. Remove the bottom hose on the tank in the same manner. Any excess coolant in the tank will drain out of the bottom hose into the pan.
Place an adjustable wrench on each mounting bolt on the tank. Turn each bolt counterclockwise to loosen and pull straight out to remove them. Most vehicles have one bolt on each side of the tank.
Pull the expansion tank out of the engine compartment.
Align the new plastic tank with the bolt holes. Replace each bolt and turn them clockwise with an adjustable wrench to tighten them.
Push the top hose on the bottom of the tank. Turn the screw in the hose clamp clockwise to tighten the hose in place. Repeat this process for the top hose clamp.
Remove the radiator cap in a counterclockwise direction. Fill the radiator with 50 percent water and 50 percent antifreeze.
Start the vehicle and let it idle to obtain the normal operating temperature. Refill the radiator to the bottom of the neck. Fill the radiator tank with the same coolant mixture to the "Hot" mark on the tank. Snap the tank lid closed and replace the radiator cap.
