For 1990-2009 cars

The cooling system has a separate plastic, translucent coolant recover reservoir. The reservoir, also caller a recovery tank or expansion tank, is partly filled with coolant and is connected to the overflow tube on the radiator fill neck to the reservoir by the overflow tube. The coolant in the engine expands as the engine heats up. Instead of dripping out the overflow tube onto the ground and being lost from the cooling system completely, the coolant flows into the reservoir.

When the engine cools, a vacuum is created in the cooling system. The vacuum siphons some of the coolant back into the radiator from the reservoir. In effect, a cooling system with a recovery reservoir is a closed system. Coolant can flow back and forth between the radiator and the reservoir. This occurs as the coolant expands and contracts from heating and cooling. Under normal conditions, no coolant is lost.

An advantage to the use of a coolant recovery reservoir is that it eliminates almost all air bubbles from the cooling system. Coolant without bubbles absorbs heat much better than coolant with bubbles in it. Although the coolant level in the recovery reservoir goes up and down, the radiator and cooling system are kept full. This results in maximum cooling efficiency.