Water Pump Question

[smoke33]

I have a 93 Johnson 25 hp with a new impeller. With the muffs hooked up I do not get any water coming from the tell tail. But, if I put the motor in a garbage can filled with water, water comes out of the tell tail as it should. Why is that?


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[MrGiggles]

I have a 93 Johnson 25 hp with a new impeller. With the muffs hooked up I do not get any water coming from the tell tail. But, if I put the motor in a garbage can filled with water, water comes out of the tell tail as it should. Why is that?


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My Suzuki is the same way.

Some muffs don't seal well to certain lower units. Supposedly the round style work better than the ones that are rectangular.

 

[DaleH]

Sounds like the OP might have poor water pressure from their hose. For muffs, I think the optimal design depends on the motor, like on V6s and above I use rectangular dual-feed muffs. On some smaller OBs the round cuff part seems to fit the best.

But I only use muffs to confirm it will start or not or pee ... but never diagnose anything whilst running on muffs. With the LU immersed in water you get the exhaust backpressure the OB normally operates at.

 

[smoke33]

Water pressure out of my hose is fine. I tried it turned up all the way as well as lowering the pressure.


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[Pappy]

By chance are you trying to use the rectangular shaped muffs? Talking about the single inlet ones.
If so, pitch them and purchase the round ones. Much better.
We have seen this with the rectangular ones too many times to count.
Also on some of the gearcases there are are two small aux cooling holes that are located just under the cav plate (in the radius) and above the water inlets. If you have low water pressure these will suck air and keep the impeller air bound.

 

[smoke33]

I do have the rectangular muffs and the hose line sends water to both sides. I will have to look at the inlets next weekend.


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[Pappy]

You did not answer whether or not you have a single inlet set of rectangular muffs.
The observation that water gets to both sides is not a "test" of whether they work or not.
The pump is not a self priming pump and needs both volume and pressure to get the water up to the pump in sufficient volume to prime the pump.
You are asking for answers and answers are being given.

 

[smoke33]

I guess my description wasn’t clear. The hose connects to a line that splits into two lines and each line goes to each muff supplying water to both sides which are rectangular.


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[Pappy]

Well.....
If you do get water coming out of the tell tale when the engine has the pump submerged (in a bucket) and no water coming out while on the muffs I would suggest changing out the muffs for the above reasons. They are cheap.

If the engine has not had a water pump recently you may want to consider changing it out. Running it un-primed can definitely affect the pump longevity.
Things to check for if you go down this road.
Grooves in the lower wear plate or upper cup. Change out the complete pump as these affect the ability to pump and prime.
Cup has signs of melting into the plastic housing. Change out the complete pump.
Purchase OEM parts, not aftermarket. The fit is much better.

 

[smoke33]

Thanks Pappy. Yes, I replaced the whole pump assembly and impeller.


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