wsm STW37 Workshop Manual page 77

STW34, STW37, STW40, WSM
2. COOLING SYSTEM
Bottom bypass system is introduced in 03-M Series
for improving the cooling performance of the radiator.
While the temperature of coolant in the engine is low,
the thermostat is held closed and the coolant is allowed
to flow through the bypass pipe and to circulate in the
engine.
When the temperature exceeds the thermostat valve
opening level, the thermostat fully opens itself to prevent
the hot coolant from flowing through the bypass into the
engine.
In this way, the radiator can increase its cooling
performance.
(1) Thermostat
1-M2
ENGINE
(A) Thermostat Closed
(B) Thermostat Open
9Y1211109ENM0002US0
KiSC issued 11, 2014 A