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Solved problems · Electrical · Crew answer

Why does my boat engine click but not crank?

A single click with no cranking usually means the starter isn't getting enough current: a weak battery, a corroded or loose cable, or worn solenoid contacts. Here's how to test it safely.

Symptom

Turning the key gives one click, or rapid clicking, but the engine doesn't turn over. Lights may dim when you try.

Likely cause

The small control circuit is reaching the starter solenoid, which clicks, but the heavy current path to the starter motor isn't delivering enough current. The usual culprits are a discharged or failing start battery, corroded or loose battery or ground cables, a high-resistance battery switch, a poor crimp, or burned contacts inside the solenoid. A starter motor that is seized or worn can do the same.

Stop now if

A cable, terminal or battery switch gets hot, you smell burning, or the battery case is swollen or hissing. Stop trying to start it. Also stop if the engine feels locked and won't turn even by hand with the wrench on the crank pulley, since water in the cylinders can do that.

The fix, in short

  1. Check the battery first. With everything off, a charged 12 V lead-acid start battery reads roughly 12.6 V. Charge it fully before going further, because a flat battery makes every other test misleading.

  2. Measure voltage at the starter while cranking. Have a helper turn the key while you read volts between the starter's main terminal and a clean spot on the engine block. Yanmar's starter test treats less than about 9.5 V here as a sign of voltage being lost between the battery and the starter. Keep hands, hair, loose clothing and meter leads clear of belts and pulleys while it cranks, and be ready to stop the engine if it starts.

  3. Find the voltage drop. Still cranking, measure across each part of the circuit: battery post to starter terminal on the positive side, and battery negative post to the engine block on the ground side. A healthy cable run loses only a fraction of a volt. Large readings point to the connection or switch to clean.

  4. Make the circuit dead before you clean it. Turn the battery switch off and remove the negative battery cable before unbolting any starter or battery connection. The starter's main cable is usually unfused, and a dropped wrench can arc and burn.

  5. Clean, tighten and protect connections. Take each lug off, clean it and the post to bright metal, refit it tight, and protect it. Replace any crimp that is green, loose or swollen under the insulation.

  6. Send the starter or solenoid out if the voltage is good. If full voltage reaches the starter while cranking and it still only clicks, the solenoid contacts or the motor are worn. Have it rebuilt or replaced.

Written by Sailor Cruiser crew. General guidance, not an inspection of your boat.

Equipment involved

  • Starting circuit: Start battery, battery switch, cables, engine ground, solenoid and starter motor

Related guides

Sources

Background reading we checked while writing this answer. The wording above is our own.

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