Saturn 2007 Ion Owner's Manual page 303

Notice: In cold weather, water can freeze and
crack the engine, radiator, heater core and
other parts. Use the recommended coolant and
the proper coolant mixture.
CAUTION:
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You can be burned if you spill coolant on
hot engine parts. Coolant contains
ethylene glycol and it will burn if the
engine parts are hot enough. Do not spill
coolant on a hot engine.
1. You can remove the coolant surge tank
pressure cap when the cooling system,
including the upper radiator hose, is no longer
hot. Turn the pressure cap slowly
counterclockwise about one-quarter of a turn.
If you hear a hiss, wait for that to stop.
This will allow any pressure still left to be
vented out the discharge hose.
2. Then keep turning the pressure cap slowly,
and remove it.
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