Engine circuit breaker tripping

[RhodySailer]

Thanks Dave,
I spoke with a Westerbeke tech and he said that if the 20 amp breaker on the engine bracket was tripped, the motor should stop running, but ours kept on running both times. Maybe the problem is the 10 amp breaker on the fuel solenoid that supplies the heat up circuit. If that trips, the engine will keep running. Either way, our issue is apparent with longer run times and warmer engine area, but no problems when cold-stating (yet).
I ordered the two new CBs, but will look into others with higher temp rating.
Dave from Rhody

[Mickeyrouse]

Westerbeke uses pretty much the same circuit on all of their current engines, so what applies to one will probably apply to all.
I encountered extremely similar symptoms on our 55B4. Engine would shut off at unpredictable times. Always would re-start after re-setting the circuit breaker. I eventually changed just about everything in the circuit other than instruments. After the problem persisted even with both wiring harnesses replaced, I observed what the problem was: upon starting the engine and letting it run at idle at the dock, I saw a faint spark (arc) between the exhaust manifold and the main wiring harness. Sure enough, there was a worn spot in one of the wires in the harness where it sparked, thus shorting out the system causing the 20 amp breaker to trip. I insulated the wire with tape, enclosed the harness with wire loom (from any auto parts store) suspended the harness, and haven’t had that problem in the four years since. It was maddening to find, and eluded me for three or four years, including interrupting one two week cruise and canceling another. I checked the harness I removed and found a similar worn area.
That which doesn’t kill you will make you stronger and smarter.

[capt jgw]

Originally Posted by Ecos

That is not how I would set up a boat. You only need to energize a solenoid for a few moments to shut off the fuel to the engine. Then it quits. You don't need to rely on an energized solenoid for your engine to keep running. Stupid on a sailboat.

Some buyers want the engine to act like it was in a car. Turn the key to start, turn it the other way to stop. Not smart enough to push a button or pull a cable to shut it off. Convenient when it works, but that won't last long on a boat.

[RhodySailer]

Thanks, Mickeyrouse et al., for the info on the wiring wear and spark. I'l have a closer look.
But why would my engine keep running? The Westerbeke tech said the motor should stop if the 20 amp breaker was tripped. I see the instruments lose signal, but the motor continues to run. When I shut it off by the normal procedure, and try to restart, it appears dead. The circuit breaker is tripped, so I reset and it starts right up (only after the engine cools a bit). It may be the 10 amp breaker for the heat button. I will look for wire wear and replace both breakers, and see what happens.

[Mickeyrouse]

What’s supposed to happen is if the 20 amp circuit breaker is tripped, the effect is the same as the key being turned off, thus de-energizing the solenoid that keeps the fuel injectors/injector pump operating, in effect the same thing as pulling the manual fuel knob. Sounds like somehow the wiring for that solenoid has been re-routed if the engine keeps running. But if you pull the manual fuel knob which should immediately starve the fuel supply, thus killing the engine, and that still doesn’t stop it, then you have other issues.

[Scrimshaw4]

The circuit breaker will also trip when there is a Resistance load on the starter. This can be cause by a bad starter solenoid or a dead spot on the starter motor. Additionally the resistance is also caused by corrosion on the connections between the start / preheat buttons and the solenoid and circuit breaker. The spec for this breaker is 20 amps.

[RhodySailer]

Problem solved! The cause was similar to Mickeyrouse's issue. There was a normal wire junction hanging near the alternator that caused the short-circuit. When the engine was warm it would hang closer to the housing and cause a spark. The key to finding it: I tried to START THE ENGINE IN TOTAL DARKNESS, in a whim before leaving the boat after failing to track it down. I saw a flash next to the engine and multiple tries showed the same spark. The gremlin was identified. Some insulating tape restored all functions to normal. As before, the breaker was speaking up and the solution was a simple one.