Volvo Penta AD31 Owner's Manual page 29

COOLING SYSTEM
INHIBITING FRESH WATER COOLED ENGINES
Regular maintenance and servicing of the cooling
system is an effective way of preventing damage
from overheating. It is also important to inhibit the
cooling system for the lay-up season in order to
avoid frost damage and corrosion.
Work on the cooling system is best carried out
on land. Otherwise there is a risk of water getting
into the boat.
The fresh water cooled engine has two cooling
systems. The engine block and cylinder head are
fresh water cooled. But the oil cooler, heat exchanger
and, on some engines, exhaust pipes, are sea water
cooled and should be inhibited in accordance with
the section on sea water cooled engines.
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