Evinrude & Johnson E75DPLSCB, Service Manual

Page: 195 / 349

193
COOLING SYSTEM
OPERATION
10
OPERATION
All models use a two-stage cooling system
design. The cooling system is dependent on water
pump pressure and controlled by thermostat and
pressure valve operation.
IMPORTANT:
Restricted or inadequate water
flow through the outboard reduces cooling system
performance and may lead to severe powerhead
damage.
Cylinder Block / Cylinder Head
Cooling
The flow of water through the cylinder block and
cylinder heads is controlled by a thermostat and a
pressure relief valve. The pressure valve is
located in the top of the block next to the exhaust
cover.
The thermostat and pressure valve control the
flow of water entering the vertical water passages
of the cylinder head.
At low speed
, the pressure valve is against the
seat and the thermostat is closed. Warm water
from the cylinder block gradually migrates to the
thermostat pocket at the top of the cylinder head.
The thermostat opens when the water tempera-
ture reaches approximately 143°F (62°C).
When the thermostat opens, water flows down
through the cylinder head to a passage in the cyl-
inder block. Water flows through the block to the
exhaust housing and then out of the outboard.
At higher speeds
, water pressure opens the
pressure relief valve at approximately 1800 RPM.
Water flows through the valve to the cylinder head
and bypasses the thermostat. All water flows
through the cylinder head to the outlet passage of
the block and then exits through the exhaust
housing.
This pressure controlled water outlet circuit pro-
vides a “high flow” discharge of water during high
speed operation.
EMM
and Vapor Separator
Cooling
Cooling water is routed from the top of the cylinder
block to the inlet fitting of the
EMM water cavity.
Cooling of the EMM helps to stabilize the temper-
atures of internal components.
IMPORTANT:
Improper EMM cooling will acti-
vate service codes 25 and 29 and the Engine
Monitor warning system. Refer to the
EMM
Ser-
vice Code Chart
at the back of this manual for
specific service code information.
Cooling water from the EMM is routed to the water
inlet fitting of the vapor separator water cavity.
Cooling the vapor separator fuel chamber mini-
mizes fuel vaporization.
Cooling water from the vapor separator is routed
to the overboard indicator.
1. Thermostat
2. Pressure valve assembly
002441
1 2
1. Overboard indicator 002457
1