A plastic surge tank connects to the cooling system with two hoses. During vehicle use, the coolant heats and expands. The coolant displaced by this expansion flows to the surge tank. The tank mounts at a point higher than all of the other coolant passages in order to provide air bleed for the system.

The surge tank contains a coolant level sensor at the bottom of the tank. When the coolant in the system falls below the recommended level, a message of CHECK COOLANT LEVEL displays on the Driver Information Center (DIC).

Caution: With a pressurized cooling system, the coolant temperature in the radiator can be considerably higher than the boiling point of the solution at atmospheric pressure. Removal of the surge tank cap, while the cooling system is hot and under high pressure, causes the solution to boil instantaneously with explosive force. This will cause the solution to spew out over the engine, the fenders, and the person removing the cap. Serious bodily injury may result.

The surge tank uses a plastic pressure-vent cap to allow a buildup of pressure in the cooling system. The cap allows the system to operate at a higher than atmospheric pressure. This pressure raises the boiling point of the coolant.

The pressure-type cap contains a blowoff (pressure) valve (2) and a vacuum (atmospheric) valve (1). The cap protects the radiator by relieving any pressure that exceeds design limits.

In order to prevent radiator collapse, caused by vacuum as the engine cools, the vacuum valve prevents excessive pressure differences from occurring between the cooling system and the atmosphere.

The surge tank cap has a new threaded design to allow for easier and safer removal. Do the following In order to safely remove the cap from a cool system:

Caution: If there is evidence of steam, do not open the hood until the steam is dispersed as bodily injury could occur.

1. Slowly rotate the cap counterclockwise ¼ turn and then stop, do not press down.
2. Allow any residual pressure, indicated by a hissing sound, to be relieved.
3. After the hissing stops, continue to rotate the cap counterclockwise until the cap is removed.

There is no specific orientation of the lettering on the cap versus the cap being tight. Retighten the cap using hand tight pressure.