I have an 06 Triton TR 186 with 150 Opti. I have been contemplating on how the water got in my tank. Mechanic thought it may have been contaminated oil, but I use factory OEM DFI oil and put the full jug in every time. I understand the pressurized system and that if it had a major leak then it would stop transferring oil to the top tank. I did have an issue with this one time about a year ago. I topped off the top tank and monitored it. It stayed about 1" from completely full until it blew #6. This was after a year though. The water was in both tanks, so it had to be transferred up to the top

I'm thinking it was getting in around the external fill spout at rear of the boat. I'm capping the fill spout off and turning the oil tank half around. Then I'm putting a new cap on the tank and will fill tank from now on, directly into the tank inside the boat. Slight inconvenience, but a big piece of mind.

My question for y'all, is there anything I'm missing here. I know y'all are a wealth of knowledge and experience. I can't afford another power head.

My old Yamaha 2000 OX66 blew the power head, due to water contamination, the culprit was a small crack on top or side( can't recall) of oil tank.
Luckily it was warrantied. Do a fine inspection of oil tank.

Thanks. I will check it out.

You're on the ball. I despise remote fill oil tanks for Mercury. They always leak. Usually air. You understand the system. Put a cap on the tank and fill it with a funnel. Yes, a pain, but worth it.

Never had a problem with it until I did. Very expensive lesson learned. I just don't want to afford it twice..

Thanks for feedback.

If you had water in the oil that was ingested by the engine, you'd have more damage than one cylinder. It would show in rod and main bearings and cylinder wall.

I'm not sure on the bearings. We checked compression and #6 was 0 and 2 others were in the 90s with some metal on plugs. The rest were still at 120 though. It was trashing the power head.