Volvo Penta D4 Operator's Manual page 64

Maintenance. Seawater system
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Cleaning seawater filter.
WARNING! Risk for water penetration.
Screw off cover (1) and remove seal plate (2). Lift out
and clean the insert (3).
IMPORTANT! If the boat is used in water that
has a lot of contaminants, seaweed etc. the filter
must be checked more frequently than indicated
in the maintenance schedule. Otherwise there is
a risk the filter will clog and the engine will over-
heat.
Draining the seawater system
Use a suitable receptacle while draining.
Open the drain nipple (1) by carefully screwing the
nipple. Use a no. 17 block spanner if the nipple sticks.
Drain all coolant and screw in the nipple by hand.
Move the hose and then continue to drain the coolant
from the drain nipple (2) and (3).