GMC T-Series 1999, Owner'S Manual, Page: 169 / 344

yellow blue
5-21
How to Add Coolant to the Radiator
1. You can remove the
radiator pressure cap
when the cooling
system, including the
radiator pressure cap and
upper radiator hose, is
no longer hot.
Turn the pressure cap slowly counterclockwise until it
first stops. (Don’t press down while turning the
pressure cap.)
If you hear a hiss, wait for that to stop. A hiss means
there is still some pressure left.
2. Then keep turning the
pressure cap, but now
push down as you turn
it. Remove the
pressure cap.