Onan MJA Series Service Manual page 23

21
COOLING SYSTEM
given in the engine data section, Sect 3.
If
water flow is below
minimum, check pump operation and inspect the passages and
'water lines for
2.
Air leaks are
an
important cause of premature impeller failure.
To test for air in the cooling system, run the engine, insert the
cooling system outlet into a tank of water and watch for bubbles.
If
bubbles appear, inspect the cooling system thoroughly to find the
source.
3.1. 3 REPAIR
Whenever making repairs on the
cooling system, tighten all connec ­
tions thoroughly. Permatex or
use
thread sealing compound on
all threaded connections. This is
especially important because of
the damage air can cause.
All water lines should be 1/2"
inside diameter or larger. Long
runs of pipe or hose need larger
inside diameter to reduce resis ­
tance. Remember, the final test
is always correct water flow.
3.1.3.1 Thermostat. - A thermo­
stat is located on the side
g
e
~
of each cylinder head, connected FIG 3. 1. C - THERMOSTAT REMOVAL
by tubing to the water cooled
manifold. If the thermostat is damaged by corrosion or other causes,
replace it.
Check the thermostat operung and closing with a thermometer in a water
bath. The thermostat should start to open when the water temperature
reaches 145
0
F and be fully open at 165
0
F. Lift it out of the water and
it
should close in a short time.
If
the thermostat doesn't operate prop ­
erly, replace
it.
3.1.3.2. Water Pump. - The water pump is a positive-displacement,
rubber-impeller type located on the upper left corner of the gear cover.
This applies to pump having plain-type bearings.
A. Disassembly
1. Loosen the pump's end plate screws and remove the end plate.
2. Pull the impeller and shaft out with a pair of pliers.
3. Ii further disassembly is necessary, remove the pump from the
engine by loosening the 2 capscrews on its mounting base.