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Solved problems · Generator · Crew answer

Why does my boat generator keep shutting down?

Most marine generators shut down to protect themselves: low raw-water flow, high exhaust or coolant temperature, or low oil pressure. Read the fault, fix the cause, and watch for carbon monoxide.

Symptom

The generator starts but shuts off after a few seconds or minutes, or stops under load, sometimes with a fault code or flashing light.

Likely cause

Marine generators have safety switches for high exhaust temperature, high coolant temperature and low oil pressure, and some for raw-water flow. Westerbeke lists a clogged seawater strainer, a dirty heat exchanger and a clogged water injection fitting as common causes of overheating. Low oil, a worn impeller, fuel starvation, an overload on the AC side, or a fault in the safety switch or its wiring can also shut it down.

Stop now if

A carbon monoxide alarm sounds, anyone feels headache, dizziness, nausea or unusual sleepiness, or you smell exhaust inside. Shut the generator down, get everyone into fresh air on deck or ashore, open hatches, and call for help (911 or VHF 16) if anyone has symptoms. Don't go back below until the alarm has cleared, and don't run the generator until the exhaust system has been checked. Never silence or disconnect a CO alarm to keep running.

The fix, in short

  1. Read the fault. Note any fault code, blink pattern or warning light. Onan's operator manual, for example, lists blink codes for faults such as loss of raw-water flow and low oil pressure.

  2. Check raw-water flow. With the generator off, close the seacock and clean the strainer. Reseal the lid and reopen the seacock before you restart. Look for a strong flow of water at the exhaust within a few seconds of starting, and shut down if it doesn't come.

  3. Check the impeller and heat exchanger. Inspect the raw-water pump impeller and replace it if vanes are cracked or missing. A heat exchanger or water injection elbow clogged with scale also causes high temperature shutdowns.

  4. Check oil and coolant. With the engine cold, check the oil level and coolant level. Don't open a hot coolant cap.

  5. Reduce the load. If it shuts down only under load, turn off big AC loads and see if it runs. It may be overloaded or short of fuel.

  6. Test the safety switches. If flow, oil and temperature are all good, a dealer can test the shutdown switches and wiring. Never bypass a shutdown switch to keep it running.

  7. Keep CO alarms working. Fit a marine-rated CO alarm in every sleeping area, test it as the maker describes, and replace it by its end-of-life date.

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

Equipment involved

  • Generator: Marine diesel generator: raw-water cooling, exhaust, oil and coolant shutdown switches, control panel
  • Safety: Marine carbon monoxide alarms

Related guides

Sources

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

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