1999 Cadillac Eldorado Owner's Manual - Page 231
1999 Cadillac Eldorado Manual
Page 231 highlights
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 cap, but now push down as you turn it. Remove the pressure cap. 5-17