COOLANT SYSTEM
Thermostat Components and Functions
12/05
6LY3 Service Manual
7-17
© 2007 Yanmar Marine International
THERMOSTAT COMPONENTS
AND FUNCTIONS
The thermostat opens and closes a valve according
to changes in the coolant temperature inside the
engine. This controls the volume of coolant flowing
to the heat exchanger from the cylinder head and,
in turn, maintains the coolant temperature in the
engine at a constant level.
The thermostat is a bottom bypass type. It is
located in a position connected with the cylinder
head outlet line at the top of the coolant pump unit.
When the coolant temperature exceeds the
opening temperature, the thermostat opens and a
portion of the coolant is sent to the heat exchanger
and cooled by seawater. The other portion flows
from the bypass line to the coolant pump intake.
The bypass line is closed off as the thermostat
valve opens and is completely closed when the
coolant temperature reaches 81.5°C (179°F). The
valve lifts 4 mm (0.16 in.), sending all of the coolant
to the heat exchanger.
Figure 7-19
Figure 7-19
The thermostat used in this engine is a wax pellet
type, with a solid wax pellet located in a small
chamber.
When the coolant temperature rises, the wax melts
and increases in volume. This expansion and
contraction is used to open and close the valve.
0006217
(1) (2)
(3)
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(5)
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(8)
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(14)
(7)
(9)
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(11)
(15)
No. Item Measurement
1 Date of Manufacture —
2 Jiggle Valve R21.5 or more
3 Valve Open Temperature —
4 Adjustment Fittings Ø8 mm (0.314 in.)
5 Stopper Ø14 mm (0.551 in.)
6 Piston Ø6.4 mm (0.251 in.)
7 Pellet —
8 Valve t0.8 mm (0.31 in.)
9 Seat t1 mm (0.39 in.)
10 Attachment Frame t1 mm (0.39 in.)
11 Spring Ø3 mm (0.118 in.)
12 Helper Springs Ø1.8 mm (0.070 in.)
13 Bypass Valve t0.6 mm (0.023 in.)
14 Pipe Ø15 mm (0.590 in.)
15 E-Snap Ring E9
Thermostat Specifications
Opening Temperature 69-73°C (156-163°F)
Full Open Temperature 85°C (185°F)
Valve Lift at Full Open 10 mm (0.393 in.)
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