GMC 2002 Yukon XL Owner's Manual page 355

Coolant Surge Tank Pressure Cap
6-34
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. See "Engine
Compartment Overview" in
the Index for more
information on location.