Directly from an Onan Manual
Section 5. Cooling
Throughout this manual, flotation water
drawn into the
for engine cooling
is called sea water Water recirculated
through the closed system will be called captive
water. Thus, confusion is avoided with other generic
terms describing water origin and use.
The MDL-series gensets use heat exchanger
The heat exchanger
is an integral part of the engine
system and is covered on the following page.
To adequately cool the genset under all conditions, the
system must be properly planned and installed.
Excess lengths of plumbing increases flow resistance
and results in reduced cooling. An air leak in the
sea water intake will reduce cooling, cause corrosion
and can even destroy the neoprene impeller in the sea
. The neoprene impeller must never be run
dry, and the pump
should be primed before initial startup
of the genset.
The water line should have a minimum inside diameter of
1 .O inch (25.4 mm) for MDL3 and MDL4 models; 1.25
inch (31.7 mm) for the MDL6 model. For runs over 20
feet (5.2 m), increase the line one pipesize for each additional
10 feet (2.6 m) of length. Water lines can be either
copper tubing or flexible hose. Be sure a length of flexible
hose is used at the genset to allow for movement,
and for noise
Because sea water cannot be relied upon to always be
clean, OnanQ recommends a water strainer or filter to
protect the engine coding system. See Figure 5-1.
Onan has a hull strainer (furnished with some muffler
kits) that can be used with a flush through-hull fitting. The
strainer (Figure SI), installed with the slots parallel to
, helps prevent pressure or vacuum when the
boat is underway. hays use aflush-type inlet with a hydrodynamic
FIGURE 5-1. SEA WATER INLET
Caution Restriction in the sea wafer Inlet line
can cause engine overheating
and shutdown. The
flush-type, through-hull wafer inlet must have an
opening at least as large as the wafer inlet line.
Stagger the genset water inlet so it is not directly in line
with other inlets. Not doing so can reduce the amount of
sea water available to the genset when underway and
. Never use scoop type water inlet fittings
with a hydrodynamic muffler
l-1 DO NOT US€ SCOOP TYPE WATER INLETS
WITH A HYDRODYNAMIC MUFFLER
Fonvard faclng scoops can develop sufficient ram
pressure to force wafer past the generafor set sea
. This can flood the exhaust
the engine cylinder. This happens when the generator
set is not running and the boat is underway. Rear faclng scoops develop vacuum which can Impede
cooling water flow.