375 Freedom Issue / Question

[jlflynn1]

Yes, what i guessed and you wrote, the fuel cooler attached on the outside of the VST.
Not really a searious problem but a lot of work to remove the VST and then the cooler housing.
I fear you should check the rectifier cooler as well as it's possible that he is clogged too.
Just for curiosity, do you flush the engines correctly after you use them?
Chris

These engines are from 2016. I bought this boat new to me this year with 325 hours on them. I do not know what the daily care of the previous owner was. Moving forward I will flush the boat every time. More importantly i will use the boat more often than the previous owner. What is the rectifier cooler? I’ll have to ask my mechanic

 

[Sardinia306Canyon]

The clogging fuel cooler affects mostly Yamaha outboards and the reason why Yamaha is not clear, most likely the design and/or position where not all water inside drain and then evaporate inside leaving deposits.

There is one thing to consider regarding flushing.
While Salt deposits will quickly dissolve at next use any mineral deposits will not and continue building up.
Once a certain amount of clogging happened the water flow will be so reduced that no dissolving will happen.
My boat is slipped and i don't know how hard the water there is, but in my house the water from the well is very hard and i would not flush the engine with that water for the reason above. So you may check water hardness before you flush regularly.
Second, there are zillions of outboards never getting flushed, or just once before winterizing because the can't flush where boat is and they don't clog or have particular high corrosion issues.
However, if your water if not hard then i would flush your engines and maybe end of season run the outboards in a tank with Redlyme added to descale the water passages.

A rectifier is a component that converts AC current from the engine's stator into DC current to charge the battery, and it is often referred to as a rectifier/regulator.

Some outboards have one, some not and rectifier is air cooled, if water cooled it has the same type as the fuel cooler and it can clog same way. I am not sure if your F300 has a water cooled rectifier cooler or just air cooled, ask your mechanic.

Chris

 

[Sardinia306Canyon]

I don't know those engines well, at all, but... that's a lot of build up. Is the VST cooler more prone to buildup than other areas? The reason I'm asking is that I'm wondering if, after seeing that, does it warrant removing the head covers?

It is a common problem on Yamaha outboards, see for example this tread in THT
https://www.thehulltruth.com/boating-forum/1303529-crusty-vst-cooler-yamaha-f300.html

As i wrote above, my guess is that fuel cooler does not drain completely and remaining water evaporates inside and leave deposits. This may depend if outboard is immediately tilted up or left vertical to drain the cooler better and faster.
AFAIK, other areas are not affected by such bad buildup, however i saw a few months a go a few years old Suzuki 25HP mounted on a samll dinghy with same buildup but at thy cylinder cooling passages and obviously engine was throwing codes. I know the owner and he say that he flush the engine every end of season for half hour while running in a bucket.
I have no idea what was the problem with his Suzuki as this is definitively not common and most of this dinghy motors don't get flushed after every use.

No head cover removal, just removing the VST - what is not very simple - and the fuel cooler sit on the back of the VST and has a flat plate as cover.



Chris

 

[DennisG01]

Yes! Using the boat on a regular basis definitely helps eliminates issues... and is MUCH more fun than not using the boat

Looking at the picture of the fuel cooler, it appears it will drain very easily.... but Chris, you bring up a good point that I wasn't thinking about. I think you may be on to something where if the engien is tilted up right away, before giving it a few minutes to drain, then I can see how water will stay trapped in there. And the hot engine will quickly evaporate the water away leaving the salt.

This is just my opinion - but it may be worthwhile to at least remove one head and check the cooling passages. It's pretty easy job (just a couple hours) on my OX66 - but I don't know, one way or the other, on the engine we're discussing. Might be worth a little time to at least investigate that.

 

[Sardinia306Canyon]

but Chris, you bring up a good point that I wasn't thinking about. I think you may be on to something where if the engien is tilted up right away, before giving it a few minutes to drain, then I can see how water will stay trapped in there.

This is just a guess as clogged fuel cooler happen mostly on Yamaha F300 and only so some boaters.
So one explication would be that there is a substantial difference between other F300 and one of them could be that engine is tilted immediately and the flushed tilted up as in the manual leaving some water inside the motor.

I always dock the boat, then switch off the engines, unload and then clean the boat and latest is to tilt up the engines and switch the battery switches off just before i leave.
Every now and then i flush the engines and in the down position as i built a always connected quick flush hose system to flush both engines together.

Chris