Other Key Items - Yamaha V-MAX SHO VF250 Maintenance Manual

ODDS and Ends

OTHER KEY ITEMS

There are a few other important things to keep an eye on. Check your
owner's manual for your particular outboard's schedule, and keep note
of when to check on them by watching your hour meter, or by using the
Yamaha Outboards app on your smartphone.
A telltale hole emits a small, visible stream of water after it has passed through the powerhead,
to help indicate that cooling water is flowing.
Tip: If water should stop flowing from the telltale hole on your outboard, or if the stream becomes weak, carefully
check the outlet tubing for obstructions. Mud daubers and other insects love to call these places home, especially
during periods of extended storage.
Tip: Not all outboards will emit waterflow from the telltale hole at idle speed, even when
operating normally. Once RPM increases a bit, however, you should see it. If you don't, keep a
close watch on your temperature gauge and listen for a warning horn. Additionally, Yamaha
outboards have an RPM reduction mode (as do most brands) which will limit the engine RPM if
an overheat condition is detected.
Tip: The rubber impeller is located inside a stainless steel cup, and uses the water for lubrication.
If this water is not present, the friction of the rubber on stainless steel will very rapidly overheat
and destroy the rubber impeller. This is why it's imperative NOT to operate, or even turn over, your
outboard without there being a proper supply of water to the outboard beforehand.
Time without use can lead to the impeller "taking a set", or becoming permanently deformed, due to
its off-center positioning inside the cup. This condition makes water flow much weaker. Additionally,
periods of non-use can cause the rubber to become more brittle, perhaps even breaking pieces off
and sending them into the cooling system. For these reasons, it's best to replace your water pump
impeller or the entire water pump assembly when servicing these items, and never rotate your
outboard's crankshaft or driveshaft in a counterclockwise direction.
26
Water Pump.
Your water pump is responsible for keeping
your engine cool. It's a simple system that
works very well. Cooling water is drawn in
through the intake grates on your lower unit,
up to and through a rubber impeller keyed to
the drive shaft on top of the lower unit, and
pumped up into the powerhead of your
outboard. There it circulates and eventually
exits back down through the propeller to help
keep it cool from the outboard's exhaust.
Volume Volume
Expanding Expanding
(Pressure) (Suction)
Pump Rotation