What is the expansion tank in your car?

Answer 1

The expansion tank retains coolant in a reservoir that's been forced out of the car's radiatior under pressure. As you run your car, the temprerature of the coolant circulating through the water jackets naturally increases causing increasing pressure in the cooling system. When the pressure builds to a high enough point, the radiatior cap allows that pressure to escape into the coolant reservoir through a small black rubber tube, called an overflow tube connected by the neck of the radiator to the expansion tank. Most of the coolant that is forced into the expansion tank returns to the radiator naturally after a few hours or when the engine is cold. If you had no expansion tank on your car, then the coolant that was released under pressure would spill out onto the road. It also helps by dissipating air bubles that have accumulated in the system. If you keep having to fill the expansion tank with large amounts of coolant every day, more than a cupfull, then there is likely a small leak somewhere else in the system. That could also be due to a faulty radiator cap (which you should always replace first before worrying youself stupid), a faulty radiator (blockage), water pump or hoses or in the worst case scenario-a blown head gasket or cracked block. If in doubt, have the radiator pressure tested at 15psi to determine where the leak is coming from, also have the radiator coolant tested with a special plastic tube contaning blue liquid that sticks in the radiator neck to measure whether exhaust gases are mixing with the coolant. It takes seconds to do and turns yellow if the result is positive leaving you with a very expensive repair for a new head gasket. If not, thank your lucky stars.