water pump test?

I did a routine water pump impeller replacement on my 1999 Yamaha 90C a couple of weeks ago and everything went fine and motor is peeing like normal. Can I effectively test the water pump/cooling by running on muffs, in a barrel, or do I need to take the boat to the lake to be dead sure? We're dragging boat to Florida over the holidays and would like to just be sure my water pump job is O.K. so we don't get down there and the temperature alarm goes off. Thanks for any thoughts on this!

Re: water pump test?

You should be fine.

Re: water pump test?

So if I just let it run on the muffs for 20 or 30 minutes and it doesn't overheat, then it most likely won't overheat running down the river at 4000RPM's? Seems like a motor that's pulling under load(like when it's in the river)would tend to overheat quicker than when it's under no load(like on the muffs)? But I just don't know.

Re: water pump test?

When you are running towards WOT the veins of the impeller bend over and it is just the shear force of the water pressure at the intake grates that provide the cooling water passage. The impeller is mainly to provide adaquate water cooling at lower rpms.

Re: water pump test?

The impeller is mainly to provide adaquate water cooling at lower rpms.

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Where in the hell did you pick up that bit of knowledge? Repeating something from some other forum?

IF that was the case, please explain why an old pump impeller with vanes that no longer straighten out like they should, will cause a motor to overheat at higher rpm.

Re: water pump test?

jeffersondodson561 said:

. The impeller is mainly to provide adaquate water cooling at lower rpms.

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So you are saying that if you could run the boat only at high speeds you can leave the impeller out of the motor?

Re: water pump test?

The vanes on my old impeller were bent over a good bit and had some wear where they contact the stainless steel cup and wear plate, so from now on I plan to replace the impeller at least every couple of years, and the job really wasn't all that tough to do. I did remove some rough corrosion deposits from the inside passages of the aluminum pump body, so I can see how these passages could get plugged up and restrict water flow. I have no reason to suspect any problems with my pump or cooling system, but just wanted to double-check the geezer's work to be sure pump was cooling correctly before our trip to Florida. Thanks guys for your thoughts!

Re: water pump test?

The manual I have (Clymers) says
"The offset center of the pump housing causes the impeller vanes to flex during rotation. At low speeds,the pump operates as a displacement type pump. At high speeds,water resistance forces the vanes to flex inward and the pump becomes a centrifugal type pump." There are also a couple of pictures showing the difference in the vanes. As far as the difference between a centrifigal vs displacement pump I am somewhat confused even with the pictures.
I think if the motor is pumping water while on the muffs your fine.

Re: water pump test?

seahorse5 said:

So you are saying that if you could run the boat only at high speeds you can leave the impeller out of the motor?

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I don't know how you would do that but if you could some how cut the veins off so the impller makes a good seal around the driveshaft, I would say that 60mph of water movement on the lower unit would certainly provide enough water pressure to activate the pressure relief valve that opens at 12 psi.

Re: water pump test?

Don S said:

Where in the hell did you pick up that bit of knowledge? Repeating something from some other forum?

IF that was the case, please explain why an old pump impeller with vanes that no longer straighten out like they should, will cause a motor to overheat at higher rpm.

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So are you saying the impeller veins are in contact with the entire water pump housing catridge at all rpms?

Re: water pump test?

I think you are full of it.
I have seen too many water pumps with the impellers still in tact but wore out that cause over heating and even those that the cup and plate are worn causing overheat.
What about the small motors that are turning full RPM but not running but 10-20 MPH
But this is just my opinion

Re: water pump test?

When I put my new impeller inside the stainless steel cup the vanes were really in there pretty tight, and with motor running seems like centrifugal force would naturally force the vanes against the walls of the cup(a good thing), so I don't see much way for the vanes to come out of contact with the cup at any time, unless the impeller is totally shot. Anyway, my motor is peeing fine and i'm going to let it run on the muffs for a while and hopefully to be sure it's cooling O.K. Thanks guys!

Re: water pump test?

99yam40 said:

I think you are full of it.
I have seen too many water pumps with the impellers still in tact but wore out that cause over heating and even those that the cup and plate are worn causing overheat.
What about the small motors that are turning full RPM but not running but 10-20 MPH
But this is just my opinion

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Well their is always the possibilty that the housing was damaged and not just the impeller. I am just saying that when working at my old place the owner did his best to save the customer a buck, so this meant that replacing the water pump with the whole kit was "too expensive", so inspecting the housing was crucial. I have never seen an impeller no matter how distorted fail at high rpms (considering it was still malible), now I have seen the housing cause overheating, but if you are the guy who replaces the impeller with the whole water pump repair kit including housing, why would you look at the housing? If the impeller is doing all the work, why the need for low water pickups? And smaller motor impellers are capable of producing enough water pressure for all rpms, much less volume to prime.

Re: water pump test?

jeffersondodson561 said:

So are you saying the impeller veins are in contact with the entire water pump housing catridge at all rpms?

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They are either in solid contact or they have a thin layer of water between them, otherwise you wouldn't be able to run engines in a test tank with a test prop on it at WOT.
You sure don't have boat speed forcing water into the intake openings when in a test tank.

Re: water pump test?

As long as its peeing it should be fine.I change my impeller every two years,and if it pees im good to go. its also a 90 yamaha

Re: water pump test?

Impellers are designed to be in contact with the housing AT ALL TIMES except for what may be considered a microspacing where water lubricates the contact between the housing and the impeller.
You would notice that the hole in the housing is not centered. In each rotation of the pump each vane moves from fully bent to extended to the max allowed in the housing, as they move from the area where the hole is close to the walls of the housing toward the further area.
As the impeller rotates the vanes move from bent to extended, and the increase in the volume of the space between the vanes, creates the suction that causes the pump to suck in water. as it continues to rotate the vanes begin to bend as they go back into the smaller area, here the space is once again reducing, resulting in the water being squeezed out of the space.
AT NO POINT IN THE OPERATION OF THIS TYPE OF PUMP DOES THE IMPELLER WORK LIKE A CENTRIFUGAL FIXED IMPELLER PUMP.
If the impeller is realy old parts of it would remain in the fully bent position so no longer providing a seal against the housing walls to allow the suction or squeeze out effects, thus resulting in an inefficency in the pump. at this point the pump tries to act as a fixed vane pump, and since its housing is not designed for this method of operation, it is ineffective and the impeller must be replaced.

To the OP if you run on the muffs for a while with good water pressure it should indicate that you would get good performance in the water, as the rpm and associated heat creation increases so does the water supplied by the pump. however if the rpm is increased on the muffs, it would reach a point where the hose would not be able to supply the required amount of water for operation. Causing engine overheat.
this however is dependant on your proper inspection of the housing as per the manual and installation of the impeller likewise.

cheers
NO Fuss

Re: water pump test?

nofuss, Thanks for your input on this, and I just didn't notice that the impeller was mounted off-center from the stainless swteel cup to create a pumping effect, must be a slight amount, seems to be more to these seemingly simple pumps than I thought. I could stand a couple of weeks in Trinidad, but might forget to come home! Good Luck!

Re: water pump test?

nofuss, I just checked my old impeller and stainless cup, and it measures about 1/8" off center, so I just learned something here about these pumps! So the constant flexing of the vanes is what's pumping and not centrifugal force, like on an automotive water pump. Of course their impellers are steel and no flex or contact with pump housing! I guess a centrifugal type pump is not suitable for an outboard motor. Thanks for your explaination!

Re: water pump test?

jeffersondodson561 said:

Well their is always the possibilty that the housing was damaged and not just the impeller. I am just saying that when working at my old place the owner did his best to save the customer a buck, so this meant that replacing the water pump with the whole kit was "too expensive", so inspecting the housing was crucial. I have never seen an impeller no matter how distorted fail at high rpms (considering it was still malible), now I have seen the housing cause overheating, but if you are the guy who replaces the impeller with the whole water pump repair kit including housing, why would you look at the housing? If the impeller is doing all the work, why the need for low water pickups? And smaller motor impellers are capable of producing enough water pressure for all rpms, much less volume to prime.

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The Yamaha water pump kits I have seen do not contain the housing, just the impeller,cup,plate,bolts, and gaskets. And just cost a few dollars more than than impeller by itself. I would not buy just an impeller just because of that and the fact that the labor is a lot more than the parts.
Yes the housing has to be looked at to make sure they are not a problem with it, but that is true with any job that is done to see if any other problems need to be addessed.
I have seen cracked vanes, broken vanes, sheared off hubs from the vanes, and some even melted down to a rubber blob. If they will not or cannot stay in contact with the cup and the top and bottom sealing surface then they are not pumping water properly.
Low water pick ups are for getting water to the pump while most of the motor is out of the water while on plane. Without the suction from the pump they would not be able to pump the water properly.
Are you saying that the small motors have a different type of pump? not sure what"much less volume to prime" has to do with pumping water at high RPMs


Robert See what you started with a simple question

Re: water pump test?

I believe that the off-center, vane-flexing nature of these pumps means that they are in effect positive displacement pumps, although they do appear to be centrifugal in nature. Seems like a pretty neat design! Good luck!