9.9 high thrust oil light comes on and oil is full.

I have a 2012 high thrust 9.9 and it was submerged for over a month in fresh water. When I pulled it back out of the water I cleaned and drained everything except the leg oil. I sprayed seafoam in the crankcase and carburetor and put fresh oil in crankcase. It fired up and ran great on the stand. When I took it out the engine oil light came on after 5 minutes and the motor began to run extremely rough. I managed to limp back to shore and when I checked the oil, it was perfectly clean and at the correct level. I put it back on the stand, hooked up the water hose and started it. It ran fine for 5 minutes and once again, oil light and rough underpowered operation. What else did I miss cleaning and how do I clean it?

The oil light indicates low oil pressure. Has nothing to do with oil quantity.

I suspect that you have a T9.9 something or other.

Keep running the motor when it is in R/M reduction mode and low oil pressure will be the least of your problems.

Thank you for your reply. Yes, it is a T9.9 XEA. 2012 model year. Is this problem most likely due to oil pump failure or is it more likely sensor or electrical in nature? The motor has very low hours. If not those, then I would think further cleaning is needed. Being there is no oil filter, and if indeed it is an issue of gunk from being submerged, where would I most likely find the place it needs cleaning? Am I dreaming to think that I can fix this myself? I have lots of experience working on cars but not marine engines. Thank you in advance for any help you can throw my way.

No oil filter but there is an oil strainer. In the oil pan.

No sensor. Just a low oil pressure switch. A gauge could be plumbed to the oil pressure switch outlet so as to determine if there is insufficient oil pressure or not.

You will never know if you can fix the motor yourself until you try.

ok, thanks again boscoe. If the problem is not the pressure switch, seeing how you can replace it with an actual oil pressure gauge, then it would have to be the screen that is clogged up as my logic tells me, because when the motor is cold, so is the oil, which would make for increased oil pressure. The pump would be flowing just enough to not trip the light. However, when the oil warmed up and became less viscous, the pressute would drop and oil light comes on as well as motor going into reduced power mode. The pump itself should be fine as the motor is nearly new and never been run with low or dirty oil. Does my logic seem to make sense? Thanks again in advance for helping me. Can you also recommend my best option for obtaining a good online repair or service manual to find this screen and clean it?

Any Yamaha dealer can get you the service manual for your model.

You can also view the Yamaha parts catalog for free. www.yamahaoutboards.com

The pump and the screen was submerged for a month you say. I have not idea if either parts have been damaged or contaminated.