Freshwater System; Coolant - Volvo Penta TAMD74A-A Operator's Manual

Maintenance: Freshwater system

Freshwater system

The freshwater system is the internal cooling system of the engine. This is a closed system and shall always be
filled with coolant which protects the engine from internal corrosion and from frost damage if the climate requires
it.
The circulation pump is responsible for circulation in the freshwater system. The thermostat begins to open at a
certain temperature and is fully open when the engine has reached its normal operating temperature. When the
thermostat opens, the hot coolant is directed through the heat exchanger, where heat is lead away via the sea-
water system (please refer to the next section).
In its standard version, the engine is fitted with an internal freshwater system. Volvo Penta also supply engines
with the cooling system prepared for external cooling, e.g. keel cooling.
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Coolant. General information
The freshwater system must always be filled with
coolant which protects the engine from internal corro-
sion and from frost damage if the climate requires it.
The corrosion protection additives become less effec-
tive as time passes, which means that the coolant
must be changed.
IMPORTANT! Never use water by itself as the
coolant. Change the coolant as recommended in
the maintenance schedule.
Water quality
The coolant must be mixed with clean water comply-
ing with ASTM D4985 to avoid any risk of blockage in
the cooling system. If there is any doubt about water
purity, use distilled water or ready-mixed coolant
ASTM D4985:
Total solid particles ................................... < 340 ppm
Total hardness .......................................... 9.5° dH
Chloride .................................................... < 40 ppm
Sulphate ................................................... < 100 ppm
pH value ................................................... 5.5–9
Silica ......................................................... < 20 mg SiO
Iron ........................................................... < 0.10 ppm
Manganese ............................................... < 0.05 ppm
Conductivity .............................................. < 500 µS/cm
Organic content, COD ........................... < 15 mg KMnO
Mn
/l
2
/l
4