60
Superior
Technology
Introduction to cooling system
While in a road vehicle the engine heat is given
off via the cooling water to the air drawn in on
the airstrain, the engine heat in a boat is
transferred to the seawater.
In order to keep the engine clear of aggressive
media such as saltwater, the Volkswagen Marine
boat engines feature a dual-circuit cooling
system.
In the same way as in passenger vehicles, the
coolant in the primary circuit is made up of
antifreeze, corrosion inhibitor and water and is
designed as a closed circuit. The heat is
transferred in a heat exchanger through which
seawater flows.
The seawater circuit (secondary circuit) is an
open circuit in which the seawater is drawn in
and after having flowed through the heat
exchangers, it is expelled again.
Overview of cooling circuit for SDI engines
The coolant circuit consists of
• Small coolant circuit (primary) – red
closed freshwater circuit
• Large coolant circuit (primary) – blue
closed freshwater circuit
• Seawater circuit (secondary) – green
Cooling system
MSSP_001_058
Seawater filter
Combined cooler
(gear oil and fuel)
Seawater pump
Exhaust manifold
Thermostat 80 °C
and coolant pump
Cooler assembly housing
Oil cooler
Coolant expansion tank
Exhaust header
Main heat exchanger
Summary of Contents for SDI 55-5
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