Yamaha 25hp 2stroke 2005 Water pump question.

[mark mcconnell]

25MSH/6L2K Yamaha25 bought new PERFECT maint. schedule. Just changed w.p. impeller. Yamaha kit #6L2-W0078-00. (do so every 100hrs). Does not pump water ! Spins correct, reassembled twice. WTF am I doing wrong ? This is not difficult. note; did not "burn" it. pulled that one 20yrs ago. Ideas ?

Worked perfect beforehand just time to replace (100hrs is my replacement point)

Reinstalled old impeller. It did not work. (no left-over parts post assembly--had to mention that in case dad reads this)

[99yam40]

what makes you think it is not pumping water?
tell tail maybe plugged up if that is what you are using for an indication

[rodbolt17]

the tell tale passage on the 2 stroke 25 is rather small and prone to corrosion/sand blockage.
loosen the T stat housing and see if water leaks out.
if it does then try to work wire or compressed air up the tell tale hole.

[mark mcconnell]

Good guess, blocked "pisser". But no they are clear (checked w/air&water). Just ordered new pump housing. Arrives wed. It's something simple, but nothing else for me to miss.

[99yam40]

with lower unit off hook up a water hose onto the pipe heading up to power head , turn on the water and see if water gets to everything it should or leaks out somewhere

Maybe left out grommet sealing pump housing to the pipe or missed the pipe when stabbed

[robert graham]

Did you replace that stainless wear plate that the impeller sits on top of?...it might have some wear/grooves in it?...

[mark mcconnell]

with lower unit off hook up a water hose onto the pipe heading up to power head , turn on the water and see if water gets to everything it should or leaks out somewhere

Maybe left out grommet sealing pump housing to the pipe or missed the pipe when stabbed

Did it (hose). Flow excellent. Replaced grommet. Proved connection by coating the grommet with silver grease, replacing lower unit then removing it. silver grease coated tube.

[mark mcconnell]

Did you replace that stainless wear plate that the impeller sits on top of?...it might have some wear/grooves in it?...

Replaced it. I know this is unbelivable. There's no more to go wrong

[robert graham]

Maybe remove/check/clean/replace thermostat and/or pressure control valve?...

[TownsendsFJR1300]

Can you put the LU in a tank of water(off the engine), hook a drill to the verticle shaft (that would go to the engine) and spin it? See if there's any water pumping out?

Obviously be careful with electric and water (or use a cordless drill)


Double check the SS cup inside the housing for correct placement, o-rings, etc..

[99yam40]

Maybe remove/check/clean/replace thermostat and/or pressure control valve?...

Come on now Robert you should know the 25 does not have a PCV and that the stat has no affect on the water pump flow into the block.

The cup is the only thing I can think of also to make sure it is in properly set. If it is not it will block off the holes and flow

[mark mcconnell]

Replaced it. I know this is unbelivable. There's no more to go wrong

Robert---Replaced thermo 1st thing.

Townsend--Checked it w/ tank of water and drill exactly as you described. Did before I wrote any of this.

99---Replacement done w/kit (1st thing). Notches and tabs place it correctly.

I've replaced thermo before discovering pump problem. while system open checked water flow, up and down, "es goot". (replaced thermo of course and it can NOT go in upside down).

New casing for pump arrives today. This little aluminum devil won't beat me.

Thanks guys. ANY ideas, ANY, are welcome. This is not a complex replacement. Getting a tattoo "WTF".

[mark mcconnell]

Robert---Replaced thermo 1st thing.

Townsend--Checked it w/ tank of water and drill exactly as you described. Did before I wrote any of this.

99---Replacement done w/kit (1st thing). Notches and tabs place it correctly.

I've replaced thermo before discovering pump problem. while system open checked water flow, up and down, "es goot". (replaced thermo of course and it can NOT go in upside down).

New casing for pump arrives today. This little aluminum devil won't beat me.

Thanks guys. ANY ideas, ANY, are welcome. This is not a complex replacement. Getting a tattoo "WTF".

Hey ! Even spun the impeller blades the opposite way (desparate). I know you can't bend them wrong-key slot on bottom of impeller-well you can but you know what I mean (tested w/drill rig).

Last clue ! Picture this. Pump assembled--looking down into the pump (through the rubber grommett) Spin the drive shaft. You can see the impeller blades turning. Correct ? Must be. cup is placed by metal tab.

[99yam40]

just make sure tab is in correct place

Housing have any signs of melting?

[mark mcconnell]

99, By tab I assume you mean the small metal tab projecting upward from the metal cup which is inverted within the housing (whew !). Yes it is in it's notch. The housing shows zero signs of melting, but I'll install new one this afternoon. It's the only thing I haven't replaced (why, don't know).

As I said this is now a personal challenge. Thanks for the ideas. Will publish results. My only real fear is the damn thing will just "start" working and I won't know why. Can't accept that one. I'll solve it.