Yamaha Water in Engine ....indicator light back on

[Viking 1]

I have a 335 Freedom with 2 Yamaha 350's. Light came on last month on starboard engine that water was present.. Water was definitely observed and replaced all the filters. After several hours of running same problem came back..Light just came back on.I live Florida where we have a lot of rain and service tech thinks this could be causing problems.He told me to check the gasket on gas cap which could be the source. Freedom gas cap doesn't have a gasket and appears to sealing properly.
Any suggestions of where water is coming from. I am going to open up the pie cover plates to gas tanks tomorrow and wash. Just read that this should be done 2 times/year. Haven't been doing this.
Only 50 gallons of fuel left so probably won't have the fuel polished. I don't want fill up and have this problem ocagain.

 

[seasick]

If you have water in the filters, replace them and have water again relatively soon, it usually means you have water in the tank. The not rinsing the tank has nothing to do with the problem and in fact could make it worse if it turns out that the sender gasket ( gas tank level sensor) is leaking. With only 50 gals of gas in the tank, gas may not leak out but water washing over the tank might leak in.
Did you replace the on the motor filters AND the water separator filters? You need to do both but if the tank has water, right now that will be a waste of money. The best way to check is to have the tank 'sticked' with a water detector paste. That entails unscrewing the sender from it's flange and sticking a stick coated with water detection paste in the tank till it hits bottom.. If there is water, There will be an obvious color change on the paste. In that case, the water form the bottom of the tank has to be pumped out. That assumes the gas above it is good but I suspect it is since the moors run after changing the filters.

I don't know what make and model fuel filler you have but all the ones I am familiar with have o-rings. Remove the gas cap it and look under the top flange on the main threaded section. There is usually a rubber o-ring. If there isn't one but the threaded portion of the cap has a groove near the top of that tube, it should have an o-ring but doesn't

 

[Viking 1]

Thanks for the quick reply.Good advice..especially about the sender gasket.I did replace both the motor filters and the water separator filter. I will double check my gas cap again to see if there is a grove where a o-ring should have been This actually happened on my fresh water filter last year. Small o-ring fell off and I never realized it and spent weeks trying to trouble shoot the air leak. Never heard of water detector paste but will bring it up with the service tech next week.
Service manager told me they have had over 10 different boats come in with similar problems..He says they all had gas cap gasket issues that let in water.
Haven't ruled out bad gas yet...I have my gas delivered directly to my boat from a fuel truck..