Cause of cooling impeller damage without water

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chickendog2010

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I have read the line below quite often but what is the cause? Overheating?

"It only takes 30 seconds without water to destroy your cooling impeller."
 
S

seahorse5

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Re: Cause of cooling impeller damage without water

friction and exhaust heat
 
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robert graham

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Re: Cause of cooling impeller damage without water

The rubber/neoprene impeller spins fast and tight inside the stainless steel pump body, without water to cool/lubricate it, just gets hot fast and melts. It's a good rule to NEVER run the motor without water, even for a few seconds. Even at idle, that drive shaft is turning in the 750RPM range and that's a lot with no water or lubrication! Good Luck!
 
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chickendog2010

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Re: Cause of cooling impeller damage without water

robert graham said:
The rubber/neoprene impeller spins fast and tight inside the stainless steel pump body, without water to cool/lubricate it, just gets hot fast and melts. It's a good rule to NEVER run the motor without water, even for a few seconds. Even at idle, that drive shaft is turning in the 750RPM range and that's a lot with no water or lubrication! Good Luck!
Click to expand...

I actually ran my outboard without water for a few seconds. :eek: I was running it in a tank and water was being pushed out and the hose wasn't making up for the lost water fast enough. But I think since it was already wet and i was just running slightly over idle speed, no major damage was done. I hit the red button as soon as i noticed no water comming out the pee hole.
 
8

82mustang

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Re: Cause of cooling impeller damage without water

Like you said, maybe cause it was already wet, and like the phrase says 30 secs, all depends. I would venture a guess that a new impeller would last longer than a something like a 5 year old one without water.

At anyrate, good thing you noticed that there was no water coming outa the tell tale and shut down. Keep in mind that you may have potentially caused some damage, and that it may still pump, but you may have some of the impeller dust in the cooling passages. I would replace the impeller, there cheap and supposed to be done yearly anyway. Nothing better than cheap insurace to keep from frying the motor. $15 vs couple of k to rebuild/replace.

Just my thoughts on it.
 
F

F_R

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Re: Cause of cooling impeller damage without water

It is probably ok since it was wet.

Ever see the smoke that comes up when somebody slams on the brakes on their car and slides the tires on the pavement? That is more or less what is happening inside a dry water pump.
 
Frank Acampora

Frank Acampora

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Re: Cause of cooling impeller damage without water

And your next logical question would be: Water is not a good lubricant. Why doesn't the impeller wear sooner?

Answer: At anything over idle speed, the water pressure inside the pump causes the vanes to bend backward away from contact with the pump wall. At this point, the pump is now acting as centrifugal, not positive displacement.
 
JustJason

JustJason

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Re: Cause of cooling impeller damage without water

I tell folks this.... Go out to your car, put it in first gear, 1 foot on the brake, the other on the gas. As soon as your tires start spinning, count to 30. After 30 shut her down and go look at your tires.... pretty, aren't they. Same thing happens to a water pump impellar.
 
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robert graham

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Re: Cause of cooling impeller damage without water

I doubt, based on what you said, that you did any real damage, of course the only way to know for sure is to remove/inspect pump. The pee stream is just an indicator and your cooling system could be just fine without it. I've cranked my motor up in the spring many times without a pee stream because the mud wasps built nest in the pee tube, a piece of wire to unplug it and it's peeing again!
 
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chickendog2010

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Re: Cause of cooling impeller damage without water

Thanks everyone for your reply! Looks like i should remove and check, just for the peace of mind. :) I am not so worried, since the outboard is brand new. I have only run it for 2hr at most. Haven't found time to take it to the river to do the break-in. I guess i will just get a 55gallon tote.
 
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Home Cookin'

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Re: Cause of cooling impeller damage without water

don't do your break-in in a bucket. You need to run it against a load. Go have fun, and explain that you "have" to.

Then when you go back for your 10 hour, get them to swith the impeller. But I doubt you need to. Although there are plenty of things you should "never" do, motors are pretty forgiving.
 
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chickendog2010

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Re: Cause of cooling impeller damage without water

Home Cookin' said:
don't do your break-in in a bucket. You need to run it against a load. Go have fun, and explain that you "have" to.
Click to expand...

Took it out for 2hr+ run yesterday. Used less than 1 gallon of 91 Shell fuel. Next time i can run full throttle for at least a few minutes. :) I am going to install the hydrofoil too. Check out my other thread (Aquamax Inflatable) for pictures.
 
kenmyfam

kenmyfam

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Re: Cause of cooling impeller damage without water

Outboard water pumps are designed to be run wet. That is why they sit in the water. Friction between rubber and steel will cause heat and rip the softest part to pieces and / or melt.
My 2 cents
 
T

tin knocker

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Re: Cause of cooling impeller damage without water

Consider that there is a difference in the density of water and air. In air the centrifical force pushes the impeller blades outward against the pump housing with a great deal of force. In water the density and resistance of water to the spinning blades of the impeller do not allow the blades to extend completely and there is very little pressure of the blades against the housing. At speed it is likely that the blades have no contact with the pump housing at all.
 
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