XL-7 2WD V6-3.6L (2007)
Coolant Reservoir: Description and Operation
Surge Tank
The surge tank is a plastic tank that the pressure cap mounts onto. The tank is mounted at a point higher than all other coolant passages. The surge
tank provides an air space in the cooling system. The air space allows the coolant to expand and contract. The surge tank also provides a coolant fill
point and a central air bleed location. During vehicle use, the coolant heats and expands. The coolant that is displaced by this expansion flows into the
surge tank. As the coolant circulates, air is allowed to exit. This is an advantage to the cooling system. Coolant without bubbles absorbs heat much
better than coolant with bubbles.