mystery question: water pump/impeller change

[TheShortAnswer]

early 2006 Yamaha f250. yes, i have reviewed HotSpots most excellent tutorial.

had a Yamaha tech do the change. first change out since new. the old one was in excellent shape and worked perfectly, but changed it anyway. took the boat and it did pee and no overheat problems. took the boat home and hooked up the hose attachment to rinse out the engine. problem is all the water gushes out the lower unit intakes. comes out about 10 times more than before. due to this, not enough pressure to send water up into the engine water jackets and out the pee hole.

the tech dropped the LU to check his work and all is fine, with no change in the problem. he is going to call Yamaha on Monday. Any ideas as to what the issue might be? really strange......we are stumped as to why the water is gushing from the LU which is why it won't bubble up into the engine. plenty of water pressure.

[cracker]

Please post the outcome as I am interested as I will be doing my first impeller change myself here very shortly...

[Florida R227]

That's really strange. I just got back from rinsing my engine (2008 F250) and I can hear the water travel up into the block then it starts to come back down, out the pee hole and then down to the lower unit. Or at least that's how it sounds. The water comes out of the pee hole on mine before it ever reaches the lower unit. Good luck finding the problem.

[TheShortAnswer]

i think i have a pretty good understanding of the plumbing and how it is SUPPOSED to work. suction (without air leaks) is the key to the thing working. yeah, you are right.......when it works the way it is supposed to, you CAN hear the water rising in the water tube and filling the water passages in the engine and coming out the tell tale (pee hole). essentially the garden hose fills the WP housing which doesn't drain as fast as it is filling and the water bubbles back up the water tube and into the water passages. somehow or another water is draining/gushing out the openings in the lower unit faster than it can rise in the water tube to make it back up into the engine. like poking a hole in the top of a can so it can vent......some how the water tube is venting and allowing free flow out the bottom of the LU.

i'll get this thing figured out.

[pmagrady]

Let us know what Yamaha tells your mechanic.

[TheShortAnswer]

finally got this thing figured out.

Yamaha.....no help.

Tech..........gave up........must be the T-stats (more $$)

i ended up putting my "plumber's hat" on and doing some detective work.......and no, i am not a plumber. i dropped the LU and tapped off all the drain holes. i filled the plastic housing with water and bingo.......problem found and corrected.

yes.....it very well maybe a Yamaha problem. a new o-ring vendor perhaps?

see the bigger of the 2 o-rings. there is a pretty good groove for the larger o-ring except near the bottom of the pic. at that point the groove is deep along the outer edge, but the lip of the groove is very shallow on the inner edge. the problem is the o-ring is just slightly too small. slightly too big would have been better.....but hey....it is what it is. you can use grease to stick it in place but the weakest point being the shallow groove it will pull out and into the cup before you can sandwich it to the wear plate. what i had to do was stretch the o-ring which gave me a couple of minutes to get the thing bolted down on top of the wear plate. as long as the o-ring is in the groove, the wear plate will keep it there when you tighten the bolts.

she pees like a race horse now.

[cracker]

I was wondering if it might be the o- ring after you posted this... That was the only thing I could think of that would such a malfunction. Glad you found the issue.

[autobaun70]

those odd shaped o-rings are a pain. I usually just put a really thin coat of silicon on the cup, and put he o-ring in it and let it set up before installing. Done that several times on my OMC as well as my brothers & parents 2 yamaha's with no problems.

[cracker]

One of tricks I have heard of is put a drop of instant glue on the corners.

[autobaun70]

One of tricks I have heard of is put a drop of instant glue on the corners.

This also works very well as long as the orings have not been soaked in oil for shipping. Super glue won't harm the rubber of most orings, or so I've been told.