Jeep 2004 Grand Cherokee Owner's Manual page 272

272 MAINTAINING YOUR VEHICLE
Cooling System Pressure Cap
The cap must be fully tightened to prevent loss of
coolant, and to insure that coolant will return to the
radiator from the coolant reserve tank.
The cap should be inspected and cleaned if there is any
accumulation of foreign material on the sealing surfaces.
WARNING!
The warning words DO NOT OPEN HOT on the
cooling system pressure cap are a safety precaution.
Never add coolant when the engine is overheated.
Do not loosen or remove the cap to cool an over-
heated engine. Heat causes pressure to build up in
the cooling system. To prevent scalding or injury, do
not remove the pressure cap while the system is hot
or under pressure.
Coolant Level
Check the coolant level at least once a month or more
often in hot weather. Check the level when the engine is
at normal operating temperature. Check the coolant level
only in the coolant recovery bottle. The coolant level
must be between the FULL and the ADD mark on the
bottle.