CHEVROLET 1999 Corvette - Manual (Page 242)

yellow blue
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CAUTION:
Steam and scalding liquids from a hot cooling
system can blow out and burn you badly. They
are under pressure, and if you turn the coolant
surge tank pressure cap
-- even a little -- they
can come out at high speed. Never turn the cap
when the cooling system, including the coolant
surge tank pressure cap, is hot. Wait for the
cooling system and coolant surge tank pressure
cap to cool if you ever have to turn the
pressure cap.