Pontiac 1999 Firebird - Manual (Page 233)

yellow blue
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3. Fill with the proper DEX - COOL
R
coolant mixture.
4. Continue to fill the radiator up to the base of the
filler neck.
5. Rinse or wipe the spilled coolant from the engine
and compartment.
6. Start the engine and allow it to run in idle for
approximately four minutes. By this time, the
coolant level inside the radiator will be lower. Add
more of the proper mixture through the filler neck
until the level reaches the base of the filler neck.
7. Shut the engine off and replace the pressure cap.
Be sure the arrows on the cap line up like this.