Chevrolet 2002 Corvette Owner's Manual page 262

1. Park the vehicle on a level surface. 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 counterclockwise (left) 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. Then keep turning the pressure cap slowly,
and remove it.
3. Then fill the coolant surge tank with the proper
mixture, to the FULL COLD mark on the coolant
surge tank.
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