Yanmar 3JH4E Service Manual page 43

(5) Check the impeller of the cooling water pump (seawater pump).
1) Remove the seawater pump cover and take out
the O-ring, impeller and wear plate,
2) Inspect the rubber impeller, checking for splitting
around the outside, damage or cracks, and replace
if necessary.
Depending on the use, the inside parts of a
seawater pump may deteriorate and the discharge
performance may drop. At the specified interval or
when the discharge volume of seawater is
reduced, inspect
accordance with the following procedures.
3) Loosen the seawater pump cover set bolts and
remove the cover.
4) Illuminate the inside of the seawater pump with a
flashlight and inspect.
5) If no damage is found, reassemble the cover
6) If any of the following problems are found, take out the O-ring, impeller and wear plate. If necessary,
replace with new one and reassemble the cover.
• Impeller blades are cracked or nicked. Edges or surfaces of the blades are marred or scratched.
Note: The impeller must be replaced periodically (every 1000 hrs or four years whichever comes first).
• Wear plate is damaged.
7) If a large amount of water leaks continuously from the water drain pipe beneath the seawater pump
during engine operation, check the oil seal inside the seawater pump.
[Notice]
The seawater pump turns in the counterclockwise
direction, but the impeller must be installed by turning
in the clockwise direction. If the impeller has been
removed for any reason and must be reassembled,
be very careful not to make a mistake and turn it in
the wrong direction. Additionally, if the engine is being
turned manually, be careful to turn it in the correct
direction. Incorrect turning will twist the impeller
blades and damage it
(6) Replace the fresh water.
Be sure to replace the fresh water every year. When the long life coolant is used of the specified type,
the replacement period of two years can be obtained.
Use clean soft water and be sure to add the Long Life Coolant Antifreeze (LLC) to the cooling water in
order to prevent rust built up and freezing.
Cooling performance drops when cooling water is contaminated with rust and scale.
Even if antifreeze or antirust is added, the cooling water must be replaced periodically because the
properties of the agent will degenerate.
1) Open the three cooling water cocks for fresh water and extract the fresh water.
Note:
One drain cock is behind the belt cover. Remove the belt cover and open the cock.
the seawater pump
Cover
in
(Sea water pump)
Direction of impeller
Impeller rotating direction
27
2. Inspection and Adjustment
O-ring
Impeller
Wear plate
Pump body
Impeller