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Old 03 November 2014, 04:38   #1
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Country: UK - England
Town: Newcastle Under Lyme
Make: Mercury Quicksilver
Length: 5m +
Engine: Outboard Yamaha 50hp
Join Date: Aug 2014
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Engine testing Yamaha 50hp 4 stroke

Hi all... so I constructed a test stand for my Yamaha 50HP outboard, connected up all the controls, rigged up a fuel tank from an lawnmower, battery etc... and after a bit of cranking it fired up. :-)

Couple of problems or observations

I fitted the water intake muffs & connected the hose pipe, it seemed to take a minute or so for water to pee out of the weep hole when the engine started, is this normal ? I already replaced the water pump impeller last weekend, so this was the first time the engine has been running for about three years or so.

After a couple of minutes, the engine alarm sounded & the high temperature indication came on the digital tacho.... I'm thinking stuck thermostat ???? I'm going to look at it tonight. Obviously I stopped it straight away... it didn't feel too hot though.

When trying to raise the revs in neutral, its got a misfire I can hear it coughing and spitting back through the air intake, I'm thinking that this is most likely that the carbs are gummed up with stale fuel... as I've replaced the plugs & serviced the engine.


Otherwise I'm well happy that my test stand has worked

Mat
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Old 03 November 2014, 11:53   #2
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Country: USA
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Is the impeller installed the right way round?

Slow to pump and engine overheat points to an issue with the impeller first IMHO.
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Old 03 November 2014, 13:01   #3
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Country: UK - England
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Is the impeller directional..... it didn't seem to be ?

The old one was deformed in the clockwise direction, but the new one looked identical both ways up and round ???


Thx
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Old 03 November 2014, 16:22   #4
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Country: UK - England
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It's the thermostat... removed the housing and it was completely encrusted in crud & scale...

I de-scaled it and then boiled it in a pan, after about 10 mins it opened, then stuck open and wouldn't shut even when cold, I can press it closed and if boiled it will open, but then sticks.

I'm going to run it on the test stand with no thermostat for a while to flush all the crap out, then fit a new one.... one problem solved :-)
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Old 03 November 2014, 17:12   #5
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Country: UK - Scotland
Town: Aberdeenshire
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Make: Ribcraft 4.8m
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You might want to run the engine in a tank or a barrel without muffs so you can add vinegar and make sure the salt build up is thoroughly removed. From what I've read on US sites, they're using around 4 gallons. Only downside is disposal, as I'm sure this would need to be bottled up, not simply flush into watercourse.

Fit a new gasket with the thermostat and don't over-torque the bolts.
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Old 03 November 2014, 17:45   #6
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Yeah just been reading about using vinegar... might give it a go

Yep, going to get a new stat & gasket. :-)
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Old 03 November 2014, 19:09   #7
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For only 4 gallons, as long as it wasn't some sort of special high potency vinegar, there would be no special disposal considerations, it can go in the regular sewage. Its readily degraded in sewage treatment works.

If you are on septic, you might consider neutralizing it a bit with baking soda prior to flushing it down the toilet. When it stops fizzing its close enough to neutral.



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Originally Posted by spartacus View Post
You might want to run the engine in a tank or a barrel without muffs so you can add vinegar and make sure the salt build up is thoroughly removed. From what I've read on US sites, they're using around 4 gallons. Only downside is disposal, as I'm sure this would need to be bottled up, not simply flush into watercourse.

Fit a new gasket with the thermostat and don't over-torque the bolts.
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