What could cause fuel dilution and an oil leak? (Ford Lehman 2712E)

Question

My father bought a boat with a Ford Lehman 2712E engine, and has been battling fuel dilution all last summer. Most recently he checked the fuel rail and high pressure injection pump with the help of two mechanics. It seemed like the issue had been solved, but no. After a couple hours running the oil level had increased again.

Now after we put the boat away for the winter, and cleaned the bilge, it was black with oil after being away for a week. The boat is on land so the engine has not been run at all. Maybe the boat is on an incline compared to being in the water, and the oil was old and now flowed to the bilge. But in any case, it could only have come from the engine.

Given this new information, is there any single issue that could explain both fuel dilution and an oil leak?

Answer 1

Just a few ideas for you --

Has anyone checked and compared the temperature of the exhaust manifold at each of the four cylinders? If one cylinder is misfiring or not firing at all, diesel fuel will leak past the rings into the engine oil.

By any chance, is this engine currently filled with multi-viscosity oil such as 15W-40? This particular engine calls for single-weight diesel motor oil, and it's important for this engine to use the correct weight for the temperature range. Multi-vis becomes too thin and leaks right past the seals.

The injector pump uses its own separate supply of single-weight motor oil. Some models over the years had upper and lower plugs for filling and draining, but on some the upper hole was open to the air with a metallic gauze screen. If the oil in the injector pump is becoming diluted with fuel due to seal leaks, it would overflow through that vent and contaminate the bilge.

Side note: Just a caution not to get stuck on the idea that there has to be one single cause for both conditions. It's equally possible that oil dilution and an oil leak can each have its own cause.