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BRUNTONSAustralia

Symptom diagnosis

Boat engine overheats at high RPM

Fine at cruise, hot at the top of the range: that pattern says the load is outrunning the cooling. The cooling system gets the blame; the load side deserves the first look.

  1. 1. Over-propped engine at sustained high load

    common

    Lugging below rated RPM means maximum fuel and cylinder pressure with reduced cooling flow (pumps turn with the engine). The thermal margin vanishes exactly when you ask for everything.

    Do thisConfirm with the WOT test — an engine that can't reach rated revs is overloaded, and heat is one symptom.

    Run the WOT test →

  2. 2. Raw-water side: impeller, strainer, growth in the intake

    most likely

    The boring answer is usually the right one — a tired impeller or a half-blocked skin fitting shows up first at high demand.

    Do thisImpeller, strainer, intake, exhaust elbow — in that order, before any propeller conversation.

  3. 3. Heat exchanger scaling

    worth checking

    Years of salt scale shrink the exchanger's capacity; high load finds the limit.

    Do thisService per engine schedule; then retest under load.

Before you spend money

This one is engine-first: do the cooling checks before thinking about bronze. But if the WOT test also falls short, treat over-propping as a contributing load — fixing it drops sustained cylinder load everywhere.

Other symptoms

Engine won't reach max RPMBlack smoke under loadVibration at cruising revs

Want the numbers checked properly?

Tell the Builder about this symptom — it screens for it, and an engineer reviews every recommendation before anything is supplied.

Build my prop spec0418 327 403