1999 Cadillac Catera Owner's Manual - Page 223

yellowblue 1. 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) until it first stops. (Don't press down while turning the pressure cap.) 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. 5-15