Pontiac 1993 Sunbird Owner's Manual page 138

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 to the left 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 cap, but now
push down as you turn it. Remove
the pressure cap.
3. Fill the coolant surge tank with the
proper mix, up to FULL COLD.
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