Chevrolet 1993 Astro Passenger Owner's Manual page 217

If the overheat warning continues,
there's
one more thing you can try.
You
can add the proper
coolant mix
directly to the radiator,
but be sure
the
cooling
system is cool
before you do it.
I
CAUTION
I I
A
Steam and scalding liquids from a hot cooling system can blow out
and burn you badly. They are under pressure, and if you turn the
radiator pressure cap-even a little-they can come out at high
speed. Never turn the pressure cap when the cooling system,
including the radiator pressure cap, is hot. Wait for the cooling
system and radiator pressure cap to cool if you ever have to turn
the pressure cap.
I
A
PO425
5-1
3