GMC C-Series 2001 Owner's Manual page 199

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.
5-32
4. With the coolant surge
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.