Education on impellers

[Augoose]

Thanks to all for the assistance on my other ongoing thread - another question....

I was replacing my impeller today. When I pulled the water pump body and looked at the impeller it appears to be off-center. Why would it be designed this way? It seems to cause the fins to bend only on one side.

 

[Bondo]

Re: Education on impellers

It seems to cause the fins to bend only on one side.

Ayuh,... That's how they work....

Look at the porting on the lower plate, it might make it more clear, on How it works....

 

[Don S]

Re: Education on impellers

As the vanes expand out while the impeller is turning, they create a little bit of suction which pulls the water up into the pump through the lower pump base. Then when they squeeze down, they force the water back out through a different port out of the top of the pump housing.

 

[Augoose]

Re: Education on impellers

thank you Don and Bond-o. I was having a problem with the engine overheating (200 + degrees F) at idle. Any speed over idle the engine cooled right down (160-165 degrees F).

 

[Don S]

Re: Education on impellers

One other thing. those vanes are supposed to straighten out when removed from the housing. if the vanes don't straighten out, it will overheat. PS. they also should be replaced every other year to prevent problems.

 

[Augoose]

Re: Education on impellers

One other thing. those vanes are supposed to straighten out when removed from the housing. if the vanes don't straighten out, it will overheat. PS. they also should be replaced every other year to prevent problems.

I think that is my issue - its been sitting on the bench for about 6 hours and some of the vanes are still bent over. The PO said he had just replaced the impeller when I bought the boat from him last April, but you never know....

 

[Bondo]

Re: Education on impellers

Ayuh,... Also,... Any scrapes, 'n gouges in the bottom plate, or top cover ruins the flow...

 

[Augoose]

Re: Education on impellers

Ayuh,... Also,... Any scrapes, 'n gouges in the bottom plate, or top cover ruins the flow...

Regarding the severity of scrapes, ones that are similar in depth to grooves on a record - are those significant enough to warrant replacing the cover?

 

[wire2]

Re: Education on impellers

Technically speaking, it's not a true impeller, it's a variable displacement pump.
A centrifugal pump has an impeller. So does a turbo. But no matter.

Have the scratches taken any material off the vane edges? If so, some water will bypass, reducing efficiency, especially at lower rpm's.

 

[Augoose]

Re: Education on impellers

It doesn't appear so. The scratches are very shallow and hardly noticeable- most I can't even feel with my finger. I do not believe they are deep enough to trap enough water to keep the engine from cooling.

 

[frank246]

Re: Education on impellers

When replacing the impeller be sure it can float up and down on the shaft after the key is installed so it sets in center between the pump halves. When the impeller can not free float on initial install they wear out quicker causing scrapes.
Good luck!

 

[wire2]

Re: Education on impellers

Then the case is probably fine.
But if the vanes don't straighten when out of the case, as Don S suggested, it's time for a new one.
In fact, I have my outdrive off and in the basement to check for the same thing before spring.

 

[Augoose]

Re: Education on impellers

Thanks all - I'm definitely replacing it once I figure out what to do about the broken teeth on my vertical drive shaft.

 

[Fireman431]

Re: Education on impellers

When you replace the impeller (I do them once a season or every 100 hrs), squirt a little liquid dish soap in the housing after the impeller has been inserted. When initially starting the engine, this will keep the impeller from getting hot and destroying it until water circulates through.

 

[Augoose]

Re: Education on impellers

Great hint Fireman, thank you