Chevrolet 2010 Corvette Owner's Manual page 341

1. When the cooling system, including the coolant
surge tank pressure cap and upper radiator
hose, is no longer hot, remove the pressure cap.
Turn the pressure cap slowly counterclockwise
about one-quarter turn and then stop.
If you hear a hiss, wait for that to stop.
A hiss means there is still some pressure left.
2. Keep turning the pressure cap slowly, and
remove it.
3. Fill the coolant surge tank with the proper
DEX-COOL coolant mixture until the level inside
stabilizes at the FULL COLD mark on the front
of the surge tank.
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