Engine, electrical systems and maintenance
Engine and electrical questions reward practical knowledge: a symptom, the likely cause, the immediate action.
Four-stroke and two-stroke
Four-stroke outboards have a sump and separate oil: check the level, never overfill. Two-strokes mix oil into the fuel, commonly 1:50 (some 1:100 - follow the label); running without oil seizes the engine within minutes. Petrol containing ethanol absorbs water and degrades; use fresh fuel, a water-separating filter and a vented tank.
Cooling and fuel
A weak or missing tell-tale means no cooling water: stop. Causes are a blocked intake, a worn impeller or a stuck thermostat. Never run an engine out of the water without muffs. Fuel problems show as rough running or stalling: check primer bulb, tank vent, filter and connection before suspecting the carburettor. On petrol inboards, run the blower for four minutes before starting.
Propeller and drive
Propeller pitch sets the load on the engine; a damaged or wrong-pitch propeller causes over-revving or sluggish planing. Ventilation (air drawn down) and cavitation (bubbles from low pressure) both feel like slipping: slow down and check for weed or damage.
Electrical
12 V systems: fuses belong close to the battery, and the main switch should isolate everything except the bilge pump. Batteries in series add volts, in parallel add capacity. Never disconnect the battery while the engine is running - the alternator can be destroyed. Keep terminals clean and greased, and charge lead-acid batteries fully to avoid sulphation.
Corrosion and lay-up
Sacrificial anodes protect the drive and hull; renew them at roughly half wastage. For winter lay-up: flush with fresh water, fog the cylinders, stabilise the fuel, remove the battery and store it charged, grease the linkages.
Worked example
After ten minutes at high speed the overheat alarm sounds and the tell-tale is only a trickle. Stop, shift to neutral, switch off. Ashore, check the intake for weed or plastic, then inspect the impeller - a torn vane explains both the weak tell-tale and the heat. Pressing on to harbour would have cost a head gasket.
Traps
Revving a cold engine; ignoring the tell-tale; mixing oil by eye; disconnecting the battery with the engine running; forgetting the anodes.