The surge tank has an inlet hose to the surge tank from the throttle body heater outlet hoses and pipe. During vehicle use, the engine coolant heats and expands. The engine coolant that is displaced by this expansion occurs in the surge tank. The surge tank is mounted higher than all of the other engine coolant passages, providing an air bleed from the system. A pressure vent cap is used on the surge tank to allow a slow build up of pressure in the cooling system. The pressure created raises the boiling point of the engine coolant. The engine coolant returns to the cooling system through the outlet hose that is connected to the water outlet housing bolted on the left (front) cylinder head.

Visually check the engine coolant level in the surge tank. The engine coolant level should not fall below the FULL COLD level during vehicle operation. Engine coolant should only be added to the surge tank. Refer to Draining and Filling Cooling System (3.5L Twin Cam V6 LX5).