GMC T-Series 1999 Owner's Manual page 171

7. By this time, the coolant level inside the radiator
filler neck may be lower. If the level is lower, add
more of the proper DEX
through the filler neck until the level reaches the
base of the filler neck.
6. Start the engine and let it
run until you can feel the
upper radiator hose
getting hot. Watch
out for the engine
cooling fan.
R
-
COOL coolant mixture
yellowblue
8. Then replace the
pressure cap. At any
time during this
procedure if coolant
begins to flow out of the
filler neck, reinstall the
pressure cap. Be sure the
arrows on the pressure
cap line up like this.
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