No tell tale stream on 2014 25 hp 4 stroke

toleworks

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Aug 30, 2016
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1
Before this engine hit 20 hours the tell tale would only work intermittently. I took it to an authorized Tohatsu mechanic who replaced the impeller (not a warranty item) and it seemed to do the trick. The impeller he removed looked new, however. I ran the boat another 10 hrs over a couple of months and flushed the motor after each use. After sitting for two weeks, I went out to run the motor and again no tell tale stream. The last time I ran the motor it was fine. I use a large water filled drum to run and flush the motor. I removed the lower unit and the water pump and found an impeller that looked partially melted, like it had been run for a while without water. I ordered new gaskets, impeller, upper housing and liner and reassembled the unit. Cranked up the motor and no tell tale. Removed the lower unit and applied hose to intake screen and water flows ok. Also ran water up through the intake pipe in the upper unit and water flows freely out the tell tale
 

pvanv

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Apr 20, 2008
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Assuming your model is MFS25B. Year is irrelevant. You cannot run these motors on muffs unless you block off the sub water strainer on the underside of the antiventilation plate. If you use a barrel full of water, it needs to be a BIG barrel, say maybe 100 gallons. Otherwise, the exhaust can bubble into the water intake and you are trying to pump air (exhaust) instead of water. That will overheat the motor and burn up the pump.

If the pump housing and impeller were melted, there is the evidence that the motor was operated without cooling water. Always install a complete wp kit, not just the impeller. Comes with everything except the upper pump housing.

The 25/30B has an ECU that can tell you whether the motor overheated, and at what hour that happened. Your dealer can get a kit to connect a laptop to the motor to see the ECU memories. Many times, a telltale gets crud in it, and the motor is cooling fine (the telltale merely shows that the cooling system is pressurized)... but in your case, it's clear that the motor did overheat -- at least the water pump did.

So, if you apply water to the water pipe and the telltale flows, yet when you use the water pump it does not, it is clear that you are not pumping. That is the place to start. Is the drive key in the impeller? If that is left out, it won't pump, and the shaft turning inside the impeller can get it pretty hot very fast, melting the impeller..

Is this a long shaft model?
 

Sea Rider

Supreme Mariner
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Sep 20, 2008
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12,345
Did water tube aligned water pump round upper grommet when re installing lower leg ? What no one should do is flush an OB while sitting on a barrell for extended time periods, if barrel does not have a fresh water intake, say a garden hose filling barrel and a lower release port to maintain OB at a correct working temp. Never cool an OB with hot water...

Happy Boating
 

pvanv

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Apr 20, 2008
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Luis, Water pipe misalignment will not melt the water pump. Running without water is the only thing that will do that.
 

km1125

Chief Petty Officer
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Aug 10, 2016
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496
If you use a barrel full of water, it needs to be a BIG barrel, say maybe 100 gallons. Otherwise, the exhaust can bubble into the water intake and you are trying to pump air (exhaust) instead of water. That will overheat the motor and burn up the pump.

Never really thought about it but this makes perfect sense. I was running my NSF5A the other day in a bucket and noticed the stream wasn't as strong as I see out on the lake. Thinking about all that exhaust gas bubbling around now I see why. Seems kinda silly that they mounted the water intake right above where the exhaust gasses can leak out while idling (right in front of the prop). Underway I can see why this is not an issue.

Always install a complete wp kit, not just the impeller. Comes with everything except the upper pump housing.
What's the symptoms if you don't? I just changed the impeller because the liner looked fine.. no scratches or any evidence of wear. What can't you see on a bad liner?
 

Sea Rider

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Sep 20, 2008
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12,345
Paul,

My post has nothing to do with melted impeller, was reffering to : if having good pee while connecting water hose straight on lower water tube and no pee at all when assembling back water pump. As you mentioned forgot to install impeller key or had a unnoticed tube/pump mis alignment issue.

Could OB have picked some debris at lower leg on last outing and OP was not aware of this, if so, this will literally melt the impeller inside housing, how bad will depend entirely on speed and running time.

Have burned 2 impellers myself while boating with an Evi 15 HP, algae issues covering lower water intakes while running full hammer down, lots of powerhead smoke along liquified, near non existence impeller found inside liner.

Let's not mix 5 HP and 25 HP water issues on same thread as to follow OP's thread correctly..

Happy Boating
 

km1125

Chief Petty Officer
Joined
Aug 10, 2016
Messages
496
Paul,
Let's not mix 5 HP and 25 HP water issues on same thread as to follow OP's thread correctly..

If that was in response to my question regarding why to replace the whole kit vs just the impeller, then pretend I have the exact same motor. My question was pretty generic and it's a difference of quite a few $$ that adds up over a few years.
 

pvanv

Admiral
Joined
Apr 20, 2008
Messages
6,500
KM, The wp kit includes the plate and cup, as well as drive key, gaskets, etc. Microscopic clearances between the impeller, plate and cup can make significant differences in slow speed pumping. If working in cold clean fresh water, the pump is a likely 3-year service item, so cost is not that big an issue. If paying a mechanic to do the work, you will be in for $100 in labor, so again not that large a factor in wp work. If in salt, and doing annual work yourself, that's a different thing. In that case, check to see whether a hard-chromed cup and plate kit is available for your motor, as they will last about 2 to 1 over the standard ss parts.
 
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