Volvo Penta D4 Series Operator's Manual page 86

Maintenance
84
Freshwater System
The freshwater system is the engine's internal cooling
system that ensures that the engine operates at the
correct temperature. It is a closed system that must
always be filled with a coolant mixture in order to pro-
tect the engine against internal corrosion, cavitation
and frost bursting.
IMPORTANT!
Coolant of a suitable chemical composition must be
used all year round. This applies even when there is
no risk for frost damage, so that the engine always has
complete corrosion protection.
The use of anti-corrosion agents alone is not permitted
in Volvo Penta engines. Never use water alone as the
coolant.
The corrosion protection additives become less effec-
tive over time, which means that the coolant must be
changed at regular intervals; refer to Maintenance
Schedule page 67. The cooling system must be
flushed whenever the coolant is changed, refer to
Freshwater system, Flushing.
Volvo Penta recommend "Volvo Penta Coolant VCS,
Ready Mixed" or the concentrate "Volvo Penta Coolant
VCS" mixed with pure water according to specifica-
tions, see Water Quality.
Volvo Penta Coolant VCS and VCS Ready Mixed are
based on organic acid technology (OAT). Using other
types of coolant, such as conventional or hybrid types,
can drastically reduce the heat transfer and result in
overheating of the engine.
47702599 12-2011