OK Diesel engine gurus, I have a puzzle...
I have a 1987 Universal M25 with unknown hours, but the hour meter was installed about 395 hours ago. When I bought the boat, four years ago, it showed 175 hrs. The engine has a tendency to drop oil pressure when warm (drops from 45 to 10 PSI after several hours of running), but never overheats, and oil pressure never goes low enough to set off the alarm.
I recently installed three new injectors, and all seemed well until yesterday.
Yesterday, there was little wind on Narragansett Bay, so we motored for about 4 hours down the West Passage to Wickford. We had a nice lunch, then motored out, and raised the sails, as the wind had piped up... After making our way back up the East Passage, and passing Bristol Harbor inlet, the wind died again, so I fired up the engine again.
We ran the engine for about an hour at 2700 RPM, when suddenly it started knocking. I quickly throttled down, and the knock changed frequency. All the gauges looked normal (Oil @20 PSI, Water temp @180, Voltage @14+) I popped it into neutral, and the knock persisted. I looked over the transom, and noticed smoke (white - possibly grey) out the exhaust. I went below, and opened the engine compartment, but could not locate the source of the knock, so I shut it down.
I checked the oil - warm but the level was OK, looked for leaks - none, looked at the coolant overflow - OK. There was some oil that had escaped from the breather tube, but not a lot, and it really isn't that unusual. Because I could find nothing amiss, I started the engine again, and the knock was gone! We safely motored back to the pumpout, and then the slip (about another hour) without a problem.
What should I look out for?