Geo 1995 Prizm Owner's Manual page 182

6. Start the engine and let it run until you can feel the
upper radiator hose getting hot. Watch out for the
engine fan.
7. By this time the coolant level inside the radiator
filler neck may be lower. If the level is lower, add
more of the proper mix through the filler neck until
the level reaches the base of the filler neck.
8. Replace the thermostat, making sure it is properly
inserted, then replace the pressure cap. At any time
during this procedure if coolant begins to flow out of
the filler neck, reinstall the pressure cap. Be sure the
arrows on the pressure cap line up like this.
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