ServiceManual

ToC
05 COOLING SYSTEM
SERVICE MANUAL MARINE ENGINES
05.00.02 Closed coolant from cooling circuit (internal 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 motorblock.
The belt pulley of the pump is driven from the back of the timing belt. The pump is maintenance-free.
The engine coolant in the closed circuit of the cooling system circulates as follows:
The circulating pump (ill.2/1) of the engine feeds the coolant through the oil cooler (ill.2/2) where
thermal energy is absorbed from motor oil.
Then the coolant flows through the water jacket (ill.2/3) into the motorblock. Coolant circulates around
the cylinders. Here, thermal energy of combustion is absorbed.
Then coolant reaches the exhaust manifold (ill.2/4), flows through the exhaust manifold in a separate
channel and absorbs thermal energy from exhaust gas.
For most of 6 cyl. marine engines (excluded 256H), coolant additionally flows through the exhaust
turbocharger (ill.2/5). Here, thermal energy is also absorbed from exhaust gas.
Then the coolant reaches the thermostat housing. By means of thermostat, depending on the engine's
operating temperature, the coolant is fed to the heat exchanger or directly to the engine coolant pump.
If the engine has not yet achieved the operating temperature of 80°C, the thermostat remains closed
and the coolant is fed via contact-channel directly to the intake side of coolant pump.
This circulating circuit (ill.2/A) is continued until the coolant in the thermostat housing (ill.2/6a) has
achieved the temperature (80°C).
As soon as the temperature of 80°C in the thermostat housing is achieved, the thermostat opens and
the coolant is partially (thermostat opens according to operating temperature) transmitted to the heat
exchanger (ill.2/B). Via the contact-channel the coolant partially arrives directly at the intake-side of
the coolant pump (ill.2/A).
Only after the coolant in the thermostat housing has achieved a temperature of 90-93°C, the thermostat
(ill.2/6b) is completely open. From this time, the whole coolant flows through the tube stake of heat
exchanger (ill.2/7) in the exhaust manifold housing. Here, the warmed up coolant releases thermal
energy to the raw water circuit, and the coolant is fed via engine water pipe to the centrifugal pump
again.
The heat exchanger is an integrated component of the aluminium exhaust manifold. This component
also includes the expansion tank (ill.2/9) with coolant reservoir, required for the pressure system.
Operating pressure is regulated via excess-pressure valve (opening pressure 0,9 bar) in the cooler
cap (ill.2/10).
Coolant temperature is measured by means of sensor (ill.2/11) on exhaust manifold next to drain cock
(ill.2/12) of coolant, and transmitted to the electronic management system. If during operation the limit
(107°C) is exceeded, the electronic management system will reduce the engine power to a perceptible
extent of up to 50%.
This disturbance is indicated on the instrument panel by an audible warner (2 times/sec.).
ATTENTION:
To avoid consecutive damages, occured trouble should be analyzed and eliminated
as soon as possible.
Page COOLING SYSTEM - 4 Z001019/0_6_July 2008