DOE Expansion Tanks Are Manufactured to Original Equipment Standard.
Most vehicles have coolant expansion tanks. They are made of translucent, heat resistant plastic, which allows you to see the coolant level easily from the outside. Coolant levels must be kept between the MAXIMUM and MINIMUM levels indicated on the expansion bottle.
Expansion tanks are an integral part of the cooling system .
Expansion tanks become more brittle as they get older, and may develop hairline cracks. Cracks lead to leaks. You should visually inspect the expansion tank every time you check your coolant level, looking for any cracks or signs of leaks.
Important: do not remove the radiator cap, add coolant or do any work on the cooling system while the engine is still hot. Wait until the engine has cooled down.