1997 GMC Sonoma Owner's Manual - Page 216

. I Steam and scalding liquids from a hot cooling system can blow out and burnyou badly. They are under pressure, and if' you turn the radiator pressure cap even a little they can come out at high speed. Never turn the cap when the cooling system, including radiatorpressure the cap, is hot. Waitfor the cooling systemand radiator pressure cap to cool if youever haveto turn the pressure cap. -- --