How the water may get into the engine oil? Oil gets a muddy-grey color and water test shows high content.
Most often, the lower rubber o-ring(s) of one or more cylinder liners are leaking. This can be confirmed from within the crankcase of the stopped engine. Keep FW cooling pump running and inspect liners for signs of leakage. Once the leaking liner is identified, it should be pulled up at first opportunity and o-rings replaced.
The other possible cause is the leaking LO cooler. In this case, water gets in a lubricating oil only at an idle engine. During the operating engine operation the opposite effect normally observed - oil gets into the cooling water and accumulates in the expansion tank. This happens because engine LO pressure is higher than FW cooling pressure. Conduct a pressure test of the LO cooler with disconnected/blinded LO pipes and opened drain valves. Once the leakage is confirmed, disassemble the cooler and replace defective parts.
In case of attached FW cooling pump (mostly, on auxiliary engines) it is also possible, that mechanical seal is leaking. If the respective drain is clogged, accumulated water may leak into the crankcase. Inspect the pump and repair as necessary.
