Oldsmobile 1999 Aurora - Manual (Page 224)

yellow blue
5-16
CAUTION:
You can be burned if you spill coolant on hot
engine parts. Coolant contains ethylene glycol
and it will burn if the engine parts are hot
enough. Don’t spill coolant on a hot engine.
1. You can remove the coolant surge tank pressure cap
when the cooling system, including the coolant surge
tank pressure cap and upper radiator hose, is no longer
hot. Turn the pressure cap slowly counterclockwise
(left) about one
- quarter turn and then stop.
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 slowly, and
remove it.