Chevrolet 1998 Lumina Owner's Manual page 220

How to Add Coolant to the Radiator
LOTICE:
Your engine has a specific radiator fill procedure.
Failure to follow this procedure could cause your
engine to overheat and be severely damaged.
-
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.
Then keep turning
the pressure cap, but
now push down as you
turn it. Remove the
pressure cap.
L -
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.
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.
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