Yamaha f20 intermittent weak water flow

[lukewhiting]

Hi guys,

I'm wondering if anyone's dealt with similar before.

Weak water flow/none. The engine will pump better at lower revs or when you let off the throttle but still weak. Tell tale gets almost too hot to touch.

So far I have-
Fitted a non genuine water pump
Then a genuine Yamaha water pump
Run it without thermostat (thermostat tested okay)
Blown out all passageways with water and air (no blockages found)

Im suspecting it's an exhaust gasket issue? But never experienced it before.

Exhaust note is definitely deeper and abit louder than I'd expect for that engine. (2006 4 stroke)

If anyone's got some knowledge on this that'd be great! Would love to get the boat useable now the nice weathers here!

[Fenlander]

Is this a new to you motor or one you know the history?

Last year I scrapped a new to me similar age Johnson 15hp after a terminal overheat. I'd flushed it all ways with gearbox off and stat out but it turned out there were unseen fine silty deposits throughout the motor which even hose pressure cold water didn't shift. Then under maximum load seems these deposits shifted round to block passageways.

So I'd be wondering as a first attempt about running yours in a container with Rydlyme in case it has a similar buildup.

[lukewhiting]

Originally Posted by Fenlander

Is this a new to you motor or one you know the history?

Last year I scrapped a new to me similar age Johnson 15hp after a terminal overheat. I'd flushed it all ways with gearbox off and stat out but it turned out there were unseen fine silty deposits throughout the motor which even hose pressure cold water didn't shift. Then under maximum load seems these deposits shifted round to block passageways.

So I'd be wondering as a first attempt about running yours in a container with Rydlyme in case it has a similar buildup.

That doesn't sound good!

Yes it's a new to me engine, (November last year)I bought it knowing it wasn't pumping (nothing at the time) and assumed it was just the impeller.

I stand corrected on the age, it's actually a 2013 not 2006. I've run it in a tub for a good while with a strong mix of salt away just incase. Even when taking the stat out and cleaning it there have been no signs of deposits so far.

I may remove the outer exhaust cover on the side of the engine where the water pipes exit the block, maybe there will be signs of something in there

[Easedalenovice]

Here is a video I made about a weak tell tale. This might help

https://www.youtube.com/watch?v=iTxzUcsPmFI

[Easedalenovice]

And another one that should help

https://www.youtube.com/watch?v=OFbP0GJGOb8

[Easedalenovice]

And a better system for pumping

https://www.youtube.com/watch?v=wowDWWOqqs8

[Easedalenovice]

There is no finer way however than to remove the cooling jacket on the side usually of the outboard and scrape away the crud. Only do this if the bolts holding the jacket on will remove and not sheer off

Hope these videos help

[Fenlander]

>>I may remove the outer exhaust cover on the side of the engine where the water pipes exit the block, maybe there will be signs of something in there

Yes I think that was the area my deposits waiting like a time bomb were lurking... the thermostat area was quite clean. I'd flushed through the block mounted plug too and the hose water seemed to run through every area without issue. The only clue in hindsight, and it was minimal, all might not be well is when bucket testing during the post purchase service a couple of times the tell tale weakened or stopped only to restart after stopping the engine and prodding about.

[lukewhiting]

Originally Posted by Fenlander

>>I may remove the outer exhaust cover on the side of the engine where the water pipes exit the block, maybe there will be signs of something in there

Yes I think that was the area my deposits waiting like a time bomb were lurking... the thermostat area was quite clean. I'd flushed through the block mounted plug too and the hose water seemed to run through every area without issue. The only clue in hindsight, and it was minimal, all might not be well is when bucket testing during the post purchase service a couple of times the tell tale weakened or stopped only to restart after stopping the engine and prodding about.

Ill have a gander inside there tomorrow and come back with an update, thanks!

[lukewhiting]

So I had a quick look this evening, all clean and clear behind that cover. Didn't have much time but blew some wd40 through the passages, dribbled out the intake and exhaust happily.

Will try have a further look tomorrow but looking fine there so far....still stumped