GMC C series 2002 Owner's Manual page 200

4. With the coolant surge
By this time, the coolant level inside the coolant
surge tank may be lower. If the level is lower, add
more of the proper mixture to the coolant surge tank
until the level reaches the COLD FULL mark.
tank pressure cap off,
start the engine and let
it run until you can feel
the upper radiator hose
getting hot. Watch out
for the engine fan.
5. Then replace the pressure cap. Be sure the arrows on
the pressure cap line up like this.
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