Terry McCoy of Gainesville, Florida, asks:
"After running perfectly for years, the diesel engine on our Beneteau 331 stopped running when we were backing out of the slip. It started right up, but then stopped again—and again. I changed the fuel filters and the engine ran without a hitch until one day we were returning to the marina and suddenly it quit again. Although it started right back up and ran without stopping, I’m becoming concerned. Any thoughts?"
Nigel Calder replies:
This sounds like a fuel supply issue, but there are lots of possible sources. The filter on the pickup line inside the tank might be getting fouled and then, when the engine stops and the suction pressure dissipates, clearing itself again. You should not be filtering fuel inside the tank, so if you have such a filter installed, I’d get rid of it.
I once had a mud wasp build a nest in my tank vent that created a vacuum in the tank that would shut down my engine. Then, after the vacuum cleared, the engine would run fine again. On another boat, I had a ball valve at the inlet to the primary filter inlet that became blocked periodically. It too would clear itself as soon as the engine stopped. Many boats have another filter screen at the inlet to the lift pump. If you have one make sure it is clean. Finally, because most engines shut down electrically via the solenoid, you might have a loose connection in the power supply.
Unfortunately, intermittent faults like yours can be tough to track down, so you need patience and persistence during your search.