Many thanks to those who have responded with suggestions.
We went on across Biscay. We had the right weather and crew was available, so we changed the oil and did the crossing. I thought I could get it fixed in NW Spain, La Coruna. Mechanic there said he didn’t have time and referred us to the regional distributor in Vigo further south.
On arrival in Vigo several days later the Yanmar service supervisor and his mechanic were aboard and did a 45 minute very thorough visual inspection of the engine. They looked at the oil on dipstick and did swipes of oil on the top of the valve cover. They could find nothing wrong with the oil, and no indicaton of oil in the coolant. (Recall the French mechanic called the oil “beautiful”, these guys felt the same way). They aid there was no (visual) sign that any liquids were in the oil. They traced the cooling system looking for leaks and found none. Their conclusion: there was nothing wrong with the oil, the coolant or the engine. I got the sense that if they were from NJ they’d have said, “Fuggetaboudit”!
“But what about the lab reports”, I countered. They took copies and said they would send their write up (I have a copy) and the reports to the Netherlands Yanmar European HQ for comments/suggestions. I’ve heard nothing so far.
So, we continue on our path south and are planning on changing the oil every 40-50 hrs and continuing the lab tests.
I’ve started a very close monitoring of the coolant levels and for the last four times we’ve operated the engine I’ve seen virtually no drop in the coolant bottle (maybe a 1/6th inch--about the thickness of the mark I made on the bottle.
I have all the parts we need to do a complete tear down of the block, but I can’t seem to find a Yanmar mechanic who wants to take my money. We’ll keep trying as we move south. We have a 10 day stop in Lagos in southern Portugal and perhaps we will have word from HQ gurus by then.
If we were in the US near the guys who installed the engine and had access to all the high tech tools/methods described in some of the posts above I’m sure with time and money we could nail this problem down, but for now, the realities of long distance cruising in foreign lands prevail and we just have to keep moving so we’re positioned in November for the trade winds crossing.
I’ve had a couple of ideas that you might comment on:
1/ the engine is turbocharged and has an air cooler (seawater cooled). A small leak there could put small quantities of seawater in the intake air. The water would be vaporized in combustion and salts left on cylinder walls to find their way eventually to the oil.
2/ the rough seas we sometimes experience could be sloshing water from the muffler up the elbow. I doubt this as the installation team at NEB Portsmouth are very professional and I doubt they would not have engineered the exhaust system correctly.
3/ I wondering if my operating methods have contributed....we have a Gori prop (with overdrive) that allows us, when motoring in flat seas, to reach near hull speed at 2200 rpm (vs say 2800-2900 with the normal pitch). I’ve used the overdrive a lot (when fuel is $8 / gal one looks for savings where you can find them). The lower rpm reduces the pressure in the exhaust system and may allow a larger quantity of water to remain in the muffler when the engine shuts down. Follow that with sailing in heavy swell / rough seas (with engine off) and we may get the sloshing up into and beyond the elbow????
Will continue with updates when available.
Thanks again for the help thus far.