Chevrolet 2010 Corvette Convertible Owner's Manual page 349

If coolant is needed, add the proper DEX-COOL
coolant mixture directly to the surge tank, but be sure
the cooling system is cool before this is done.
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.
6-37