The battery box
The underhood fuse block
DESCRIPTION AND OPERATION
COOLING SYSTEM DESCRIPTION AND OPERATION
Coolant Heater
The optional engine coolant heater (RPO K05) operates using 110-volt AC external power and is
designed to warm the coolant in the engine block area for improved starting in very cold weather
-29°C (-20°F). The coolant heater helps reduce fuel consumption when a cold engine is warming
up. The unit is equipped with a detachable AC power cord. A weather shield on the cord is
provided to protect the plug when not in use.
Cooling System
The cooling systems function is to maintain an efficient engine operating temperature during all
engine speeds and operating conditions. The cooling system is designed to remove approximately
one-third of the heat produced by the burning of the air-fuel mixture. When the engine is cold, the
coolant does not flow to the radiator until the thermostat opens. This allows the engine to warm
quickly.
Cooling Cycle
Coolant flows from the radiator outlet and into the water pump inlet. Some coolant flows from
the water pump, to the heater core, then back to the water pump. This provides the passenger
compartment with heat and defrost capability as the coolant warms up.
Coolant also flows from the water pump outlet and into the engine block. In the engine block, the
coolant circulates through the water jackets surrounding the cylinders where it absorbs heat.
The coolant then flows through the cylinder head gasket openings and into the cylinder heads. In
the cylinder heads, the coolant flows through the water jackets surrounding the combustion
chambers and valve seats, where it absorbs additional heat.
From the cylinder heads, the coolant flows to the thermostat. The flow of coolant will either be
stopped at the thermostat until the engine reaches normal operating temperature or it will flow
through the thermostat and into the radiator where it is cooled. At this point, the coolant flow
cycle is completed.
Efficient operation of the cooling system requires proper functioning of all cooling system
2007 Hummer H3
2007 ENGINE Engine Cooling - H3