I had the local Yanmar diesel mechanic to the boat today, to look at why the engine was losing oil. Great news, the problem is relatively minor. The crankcase oil is cooled by seawater, and it is common for a leak to develop in the oil cooler. Since the oil pressure is greater than the seawater, oil leaks out into the seawater cooling circuit and goes out the seawater exhaust.

I was concerned that the oil consumption was via another route, past the piston rings, but thankfully that is not the case.

The mechanic also noted that the valves needed to be adjusted and the turbocharger needed to be rebuilt. Since we're in Mexico, all of this work is relatively cheap.

It feels great to know that the engine will be solid and reliable going forward.

One thing I learned, is that Yanmar engines like to run at a high RPM, around 3000 or even higher. It turns out, that our boat reaches hull speed at 2700 RPM, which indicates the prop has too much pitch. When running at a lower RPM like 2000, the engine builds carbon deposits that will shorten the engine life.