STEYR MOTORS Marine Engine 2012 Series, Service Manual

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Cooling System
Z001138-1_2013-02-01 4/21
05.00 Functional Description Engine Cooling Circuit
In the closed (primary) cooling circuit of the engine, the coolant circulates by centrifugal
pump (circulating pump) mounted at the front of engine block.
The pulley of the pump is driven from the back of the timing belt. The pump is maintenance-
free.
The engine coolant (SMO Z011785/0) in the closed circuit of the cooling system circulates as
follows: The circulating pump of the engine feeds this 1:1 Glycol mixture through the coolant
distribution manifold into the engine block. The coolant flow is split up to each cylinder in this
distribution manifold.
The coolant circulates around the cylinders, absorbing the thermal energy from the
combustion, passing through ports inside the cylinder blocks to the upper deck portion
collecting at the front outlet manifold. In the outlet manifold a cooling sensor is mounted to
inform the engine management system about the operating temperatures and conditions of
the engine. Part of the coolant flows from the distribution manifold directly into the engine oil
cooler and back to the outlet manifold.
Depending on engine operating temperature, the coolant is circulated to the thermostat and
at low temperature returned to the coolant pump starting its circulation through the block
system again.
As operating temperature increases the thermostat will gradually/proportionally reduce the
flow through the short circuit pipe. As this happen the coolant flow will decrease in the short
circuit pipe and coolant will start to flow through the radiator returning to the thermostat back
to the circulation pump.
During high load and full load operation the thermostat will completely close the short circuit
pipe and the entire coolant will circulate over the radiator back to the thermostat and coolant
pump.
The thermostat is mounted in a separate housing on the intake manifold side of the engine.
The thermostat operating temperatures are 80-95 °C. the thermostat is completely open.
From this time, the whole coolant flows through the radiator. Here, the hot coolant releases
thermal energy via the radiator.
The expansion vessel serves as a continuous bleeding system for the coolant circuits and
provides sufficient volume for the expending liquid. The expansion vessel is equipped with a
filler cap capable to maintain proper pressure in the system. Operating system pressure is
regulated via excess-pressure valve (opening pressure 1.5 bar) in the pressure cap.
Coolant temperature is measured by means of sensor on the water pump (thermostat)
housing, and transmitted to the electronic management system. If during operation the
temperature limit exceeds 107°C, the electronic management system will reduce the engine
power to a perceptible extent of up to 50%.
ATTENTION: To avoid damages on the engine, occurring trouble must be
analyzed and eliminated immediately.