I have a 6 cyl. boat with a inboard,outboard motor,merc-cruiser. The boat has been sitting for 3 years,run a few times a summer.I changed the oil and it looked like milk. After I put it in the water runs great but the oil is going someplace,I don't see it in the water and no smoke so my ? is where is it going and what is the problem and how can I fix this?