CHEVROLET 1999 Cavalier - Manual (Page 222)

yellow blue
5-16
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) about two or two and
one
- half turns. If you hear a hiss, wait for that to
stop. This will allow any pressure still left to be
vented out the discharge hose.
2. Then keep turning the
pressure cap slowly, and
remove it.