One of three different types of cooling systems is used on a Series 53 engine: radiator and fan, heat exchanger and raw
water pump, or keel cooling. A centrifugal type water pump is used to circulate the engine coolant in each system. Each
system incorporates thermostats to maintain a normal operating temperature of 160-185° F (71-85°C). Typical engine
cooling systems are shown in Figs 18 and 19.
Radiator Cooling System
The engine coolant is drawn from the bottom of the radiator core by the water pump and is forced through the oil cooler
and into the cylinder block. The coolant circulates up through. the cylinder block into the cylinder head, then to the water
manifold and thermostat housing. From the thermostat housing, the coolant returns to the radiator where it passes down
a series of tubes and is cooled by the air stream created by the fan.
When starting a cold engine or when the coolant is below operating temperature, the coolant is restricted at the
thermostat housing(s) and a by-pass provides water circulation within the engine during the warm- up period.
Heat Exchanger Cooling System
In the heat exchanger cooling system, the coolant is drawn by the circulating pump from the bottom of the expansion
tank through the engine oil cooler, then through the engine the same as in the radiator and fan system. Upon leaving the
thermostat housing, the coolant either passes through the heat exchanger core
Figure 18. Typical Cooling System for In-Line Engines