Yanmar 1GM User Manual page 171

COOLING SYSTEM
HEAT EXCHANGER
Cooling tube
165
Seawater
outlet
Seawater
inlet
Side cover
Baffle plate
Gasket ,
Freshwater inlet
(from cylinder head)
Cooling
pipe
cover
Freshwater inlet
(to freshwater
reservoir)
Side cover
coolant travels to the heat exchanger, where the heat ab-
sorbed from engine operation passes through the parallel
copper tubes to the water in the seawater system.
Engine cooling is thus accomplished without seawater
entering the engine. This eliminates the corrosion, deposit
buildup and debris accumulation that occurs in a standard
cooling system, resulting in longer engine life-espe-
cially if the boat is used in saltwater.
Like an automotive cooling system, the freshwater sec-
tion is pressurized at 13 psi. This raises the boiling point
of the coolant to permit higher operating temperatures for
increased engine efficiency.
A thermostat controls coolant circulation. When the
thermostat closes, it prevents coolant from entering the
heat exchanger, rerouting it back to the engine circulating
pump. Once the thermostat opens, it closes offthe passage
to the circulating pump and sends the coolant through the
heat exchanger before returning it to the engine pump.
This provides quick engine warm-up and maintains a con-
stant operating temperature.
THERMOSTAT
The thermostat blocks coolant flow to the exhaust man-
ifold (standard cooling) or heat exchanger (closed cool-
ing) when the engine is cold. As the engine warms, the
thermostat gradually opens, allowing coolant to circulate
through the system.
CAUTION
Do not operate the engine without a thermo-
stat. This can lead to serious engine dam-
age.
Thermostats are rated according to their opening tem-
perature. The opening temperature value is stamped on
the thermostat. The thermostat should start to open at the
temperature stamped on the thermostat and should be
fully open at 25° F (14° C) above that temperature. Check
the thermostat rating after removing the thermostat and
compare it to the specifications in Table 2.