Expansion (Recovery) Tank
systems have a separate coolant reservoir or expansion tank, also called the recovery
tank. It is partly filled with coolant and is connected to the overflow tube from the
radiator filler neck. The coolant in the engine expands, as the engine heats up. Instead
of dripping out of the overflow tube onto the ground and being lost out of the system
completely, the coolant flows into the expansion tank.
engine cools, a vacuum is created in the cooling system. The vacuum siphons some of the
coolant back into the radiator from the expansion tank. In effect, a cooling system with
an expansion tank is a closed cooling system (fig. 6-13).
Coolant can flow back and forth between the radiator and the expansion tank. This occurs
as the coolant expands and contracts from the heating and cooling. Under normal
conditions, no coolant is lost. Coolant is added in this system through the expansion tank
that is marked for proper coolant level. NEVER remove the cap located on the radiator
unless you are positive the system is cold. If there is any pressure in the radiator, it
will spray you with hot steam and coolant. Use extreme caution whenever you work around a
closed cooling system.
to the use of an expansion tank is that it eliminates almost all air bubbles from the
cooling system. Coolant without bubbles absorbs heat better. Although
the coolant level in the expansion tank goes up and down, the radiator and cooling system
are kept full. This results in maximum cooling efficiency.