Why are impellers....fragile?

[paulspaddle]

I didn't want to hijack that other thread, but for a part this so integral to a motor, why do they make impellers so fragile?

From my understanding it's not exactly 'easy' to get to, they can burn out in an instant, needs replacing either annually or every two years.

If it fails, you are stranded.

I'm sure they don't make very much money off of them so that can't be it.

For someone who knows little about the i/o this seems like a flaw in engineering.

 

[bruceb58]

Re: Why are impellers plastic....fragile?

Re: Why are impellers plastic....fragile?

They aren't plastic, they are rubber. They have to have flexible vanes in order to provide enough suction to get the water up the sterndrive, through the engine and out the exhaust with enough flow.

 

[paulspaddle]

Re: Why are impellers....fragile?

They aren't plastic, they are rubber. They have to have flexible vanes in order to provide enough suction to get the water up the sterndrive, through the engine and out the exhaust with enough flow.

Ah ok, I've never actually held one, just looked at pics.

(edited title)

Are they the same today as they were 20 years ago?

To me it still seems like something that could be re-engineered.

Sorry if I sound like a complete noob asking ridiculous questions...just curious.

 

[Fishermark]

Re: Why are impellers....fragile?

To me it still seems like something that could be re-engineered.

Actually I believe some company has in fact re-engineered them. Or at least is using a different material that supposedly is more durable and less likely to fail due to running dry.

I don't remember much about the company... I'm sure a forum search or internet search would find it pretty easy.

As to "why?" I'm sure the reason is the same as always - cheaper to manufacture the part with materials that are handy - and ensures regular maintenance. Is that a good reason? Well, I guess that's open for debate.

 

[intrepid]

Re: Why are impellers....fragile?

They probably should be , I think the volvo ones are easier to be to thru a hatch on the side of the motor .

But then you need a design that works back into the old units and that might costs lots.

This was something the original designers were not worried about. They just wanted it to run

 

[Rocky_Road]

Re: Why are impellers....fragile?

Fishermark...they are made by Globe:

http://www.globecomposite.com/pages/products_impeller

Happy boating!

 

[Fishermark]

Re: Why are impellers....fragile?

Yep - that's the one I was thinking of Rocky. I have never used them - but they are intriguing.... I may try one next time myself.

 

[lowkee]

Re: Why are impellers....fragile?

It has always seemed odd to me as well. My pool pump is able to run dry without becoming toast, why not a water pump for an outdrive? Is it an engineering issue or just a "this is cheaper" issue? As if cost was an issue, you would think a 3rd party would sell a permanent drop-in replacement pump by now. Maybe some uber-creative type on here?

 

[rbh]

Re: Why are impellers....fragile?

No impeller, regardless of the material its made of will last forever.
The problem being that your always going to pick up sand, gravel, mud ETC
and this just leads to wear, the nice thing about a rubber impeller is it is more forgiving than any other material in the short term, as well, cheaper to replace in the long run.

 

[izoomie]

Re: Why are impellers....fragile?

A pool pump uses centrifugal force and is not a positive displacement pump. The impeller does not touch anything, it just spins in space. That's why some of them need to be primed. The impeller needs to be immersed in water in order to push on something, that creates low pressure on the inlet side to draw in more water.The seal is the only thing to worry about in those. Your "run dry" pump has a seal that does not need the water to cool it.

The impeller in these motors contacts the walls of the cup and needs water to lubricate and cool the soft impeller material.

I agree that they should at lease be positioned in a way that they can be maintained without taking the motor apart.

It's a good thing there is lot's of advice on this site to walk anyone through it that wants to tackle it.

 

[Aviator5]

Re: Why are impellers....fragile?

You don't have to take motor apart to replace them,
they don't fail if properly used.
By the way, why don't they re-engineer engines to run them without oil?

 

[izoomie]

Re: Why are impellers....fragile?

Ok, it's not the motor, but imagine if you had to remove the transmission in your car every time you had to change the water pump.

I think we're just saying that something so important should be a little easier to replace.

Looks like us northerners are pining for spring.......I know I am.

 

[Expidia]

Re: Why are impellers....fragile?

I agree with the posters question as I wondered it myself. I can understand the material that an impeller is made of not being easily damaged by sand etc.

Then as mentioned in another post above why not just engineer it with a door that the user can just open and swap out with a new one every two years. Kinda like replacing your autos oil or air filter.

The reason is probably to keep the dealers shops income up would be my guess.

Here is an example: Several days ago I called the dealer where I bought my rig in 2007 and asked how much it would be for him to replace my impeller. He said around $200

I called the next certified merc dealer listed on mercs website nearest my zip code and he said about $30 for the impeller kit and another $40 labor. Said it will take him about 30 minutes to do and to bring the rig by on Sat!

I asked him to use the OEM Merc kit and he said no problem.

Moral is if you want to save a few bucks check around before you just bring it in for an impeller. I tried to do it myself and had a hard time getting at the clip on the legs connecting rod so for the extra $40 it's well worth it for me to have a dealer do it.

But, I agree, it should be more accessible for owners that would prefer to do it themselves! We own 3 merc outboards and I'd prefer to work on them myself.

 

[Aviator5]

Re: Why are impellers....fragile?

It will take not more than an hour for a handy person to change it by himself.
Sorry, I just don't see the issue here. To add a few thousands to a cost of outdrive for the sake of somebody, who burned his impeller, be able to switch it in 10 minutes?

 

[izoomie]

Re: Why are impellers....fragile?

Ok, Aviator5. You win. We'll leave it as it is.

 

[bruceb58]

Re: Why are impellers....fragile?

They should all just be like the Volvo and Bravo have it...in the engine compartment so no drive has to be taken apart.

 

[Aviator5]

Re: Why are impellers....fragile?

They should all just be like the Volvo and Bravo have it...in the engine compartment so no drive has to be taken apart.

Then how will I get 50 bucks from my neighbor every time he wants his one replaced?

 

[crawleym]

Re: Why are impellers....fragile?

I think the "other thread" was mine. Turns out I did not damage the impeller. I had to drain the oil/lube, separate the lower unit from the upper and inspect the pump/impeller. It did not take all that much time. I've been wanting to learn how to do so because I'd like to change the impeller myself the beginning of each season. The boat shop wanted $320 for parts in labor but that included some other stuff because they wanted to remove the upper unit as well. Now I have experience in replacing the impeller so if it breaks at the lake, I'll have a chance of salvaging the day/weekend.

 

[Don S]

Re: Why are impellers....fragile?

It did not take all that much time. I've been wanting to learn how to do so because I'd like to change the impeller myself the beginning of each season. The boat shop wanted $320 for parts in labor but that included some other stuff because they wanted to remove the upper unit as well.

There is a reason why they wanted to pull the complete drive for "Other things" that really need to be done. You should also be doing the impeller in the fall during winterizing, etc. etc.
Might want to start a new thread about what you want to do to find you are missing a lkot of what really needs to be done to your boat,
Let's not hi-jack this thread about it.

 

[DavidW2009]

Re: Why are impellers....fragile?

"From my understanding it's not exactly 'easy' to get to, they can burn out in an instant, needs replacing either annually or every two years."

The impeller on the Cobra outdrive is relatively easy to access. Remove the rear cover and it's right there. Don't have to drop a lower end.