Chevrolet 2002 Silverado 1500 Pickup Owner's Manual page 403

Coolant Surge Tank Pressure Cap
6-38
The coolant surge tank pressure cap must be fully
installed on the coolant surge tank.
NOTICE:
Your coolant surge tank pressure cap is a 15 psi
-
(105 kPa) pressure type cap and must be tightly
installed to prevent coolant loss and possible
engine damage from overheating.
Your vehicle may be
equipped with one of
the two caps shown.