Tohatsu outboard impeller replacement interval
The water pump impeller is the rubber rotor inside your Tohatsu outboard’s lower unit that pushes cooling water through the engine. It is small, cheap, and one of the biggest reliability items on the whole motor. When an impeller wears, hardens, cracks, or takes a permanent “set”, cooling flow drops and overheating risk climbs fast.
The water pump impeller is the rubber rotor inside your Tohatsu outboard’s lower unit that pushes cooling water through the engine. It is small, cheap, and one of the biggest reliability items on the whole motor. When an impeller wears, hardens, cracks, or takes a permanent “set”, cooling flow drops and overheating risk climbs fast.
Recommended interval (practical rule):
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Inspect every year, especially if you boat in saltwater or shallow, sandy areas.
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Replace every 1 to 2 seasons (or 100 to 200 hours) as preventative maintenance for most owners.
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Replace immediately if you do not know the history of a used engine, or if you have any cooling warning signs.
Why impellers wear out:
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Heat and friction slowly harden the rubber vanes.
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Dry running (starting without water, blocked intake, muffs not sealed) can damage it in minutes.
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Silt, sand, and debris abrade the vanes and wear the pump housing.
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Long periods sitting can flatten the vanes, causing weak flow at the next start.
Warning signs to act on: weak or intermittent tell-tale stream, higher engine temperature, steam, alarms, poor idle cooling, or a tell-tale that stops at higher revs.
Best practice is to fit a complete water pump kit (impeller, key, plate, gaskets, seals), not just the rubber rotor, and always use new sealing washers.
