231
COOLING SYSTEM
COMPONENTS
9
Adapter/Inner Exhaust Housing
• Adapts the cylinder/crankcase assembly (pow-
erhead) to the exhaust housing and the water
tube.
• Provides water passages which route incoming
and outgoing cooling water.
• Provides exhaust passages which connect to
the lower inner exhaust.
Pressure Relief Valve
A pressure relief valve is used to control water
flow and operating temperature at higher speeds
(above approximately 2500 RPM / 21 PSI). Pres-
sure relief valve activates or “blows-off the seat”
as water pressure increases. Spring tension is
used to set the “blow off” pressure.
Overheating: A restricted or faulty valve typically
results in HIGH SPEED overheating. (Minimum
water pressure at 3000 RPM is 21 PSI.)
Overcooling: Debris may prevent the valve from
closing completely.
Thermostats
Thermostats are used to control water flow and
operating temperature at lower speeds (below
2500 RPM).
Overheating: Restricted or faulty thermostats typ-
ically result in LOW SPEED overheating.
Overcooling: Debris may prevent the thermostat
from closing completely.
Refer to THERMOSTAT SERVICING on p. 233.
Block Venting
A fitting and hose from the top of the block allows
the constant movement of water and/or air from
the center water passage (top) of the block. Circu-
lated water flows through the EMM to the Vapor
Seperator and then overboard through the water
outlet fitting in the rear exhaust grommet.
1. Adapter/inner exhaust housing
2. Water tube(s)
005396
1
2
20 in. models
25 in. model
25 in. models
Pressure Relief Valve Components 005391
Thermostat 005392
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