Impeller design

[mrbscott19]

Has anyone ever had an idea that could/would lengthen the life of your impellar? <br /><br />It just seems to me that in the 50+ years outboards have been built, someone would have come up with a better material/design to keep the impeller from needing replaced every year or 2.<br /><br />I'm not looking for things people are currently doing to prolong their impeller life. I just want ideas on how one could improve the design so it doesn't need replaced so often. Seems that impellers lasting 4+ years instead of 2 MAYBE 3 would be an awesome seller.<br /><br />Better yet, can anyone tell me why they use the material they use??

 

[WillyBWright]

Re: Impeller design

Neoprene turns out to be the best on the market, even after decades since it's introduction. There have been Urethane impellers, but they get really stiff in cold water. Neoprene isn't nearly as affected by cold or heat as urethane. The one thing Urethane has over Neoprene is it's ability to run dry longer. But it's not all that much longer.

 

[novicetech]

Re: Impeller design

When you htink about it that impeller is turning 5500 rpms most of the time. it is amazing that they last as long as they do. Just my two cents worth.

 

[JB]

Re: Impeller design

There have been some interesting waterpump designs that looked like they would last, Scotty.<br /><br />Most of the ones I have seen were positive displacement types that either wouldn't pump enough water at idle or loaded the engine too much at higher speeds.<br /><br />The beauty of the flexible impeller is that it operates as an adequate positive displacement pump at idle but changes to a relatively constant pressure pump as the engine speeds up and the vanes flex.<br /><br />The truth is that most neoprene impellers would last several years if we didn't change them first. Sort of like spark plugs; if you wait to change them until after they fail you are in a lot of trouble.

 

[rwcreigh1]

Re: Impeller design

some home water pumps wear bronze.

 

[roscoe]

Re: Impeller design

Change mine every couple years. Dad refuses to let me touch his motors. I bought his 15hp from him when it was 18 years old. It still had the original impeller and it worked well. I changed it and was amazed that it had very little wear, but the vanes had taken a set pretty badly.<br /><br />Instead of a new impeller or pump design, I would like to see one that didn't require dropping the lower unit to change it.

 

[Chinewalker]

Re: Impeller design

Other pump designs have come and gone. Metal ones had problems wearing from silty water, or corroding in salty water. Plunger types would foul up in silty water and wore out quicker if used in anything other than clean water. Force feed pumps require forward motion, so they don't pump on motors with gearshifts or when trolling. Fact is, the rubber vane waterpumps, to date, are the best compromise between durability and longevity for the widest range of applications and environmental conditions. Come up with something better and you've got your million dollar idea...<br />- Scott

 

[Paul Moir]

Re: Impeller design

Around here anyway, half the reason to replace the impeller is to excersize and reseal the l/u bolts and grease the driveshaft splines. The worst part of replacing a neglected impeller is beating the poor L/U off.<br />A remote water pump sounds like a great idea. Wouldn't it be nice if they could make one that drew all the way up to the engine compartment? But I suppose that wouldn't degrade as well as the submerged type. I mean, when it starts to wear out a pump mounted high like that would never prime at all, while your regular pump will still provide some water.

 

[Scali]

Re: Impeller design

I wouldnt put much if any grease on the driveshaft spline, it doesnt compress well, very, very light coat if any.<br />I agree with your point though, it's important to drop the LU every couple years..<br />After doing this one also learns how easy it is to change 2 out of the 4 seals { which usually does the trick in stopping gearcase water intrusion } & they need replacing eventually.<br />I just did my Mercs couple weeks ago & she's pumping like a SOB !<br />Important thing to do & I think the impeller designs are a good one

 

[Moody Blue]

Re: Impeller design

My dad has a 1992 15HP Evinrude that is still running the original impeller. He puts about 50-60 hrs/year on the motor and it just keeps pumping. Don't know if the lower unit will ever come off though. Is it REALLY necessary to replace the impeller every other year ? How do you explain the motors out there like my dads that have run year after year with the original equipment ? <br />Scali, I just finished re-doing my waterpump and replaced the 2 driveshaft seals as well because I was getting water in the lower unit. Are these the seals you were refering to ?

 

[Scali]

Re: Impeller design

Rod C,<br />yeah from what I understand more often then not that does the trick when the gear oil gets a little milky..<br />Rod, <br />How did you make out with the exhaust tube ?<br />That was an interesting situation, I was wondering if they were even used in that motor .<br />alan

 

[Moody Blue]

Re: Impeller design

Scali I have continued the post on the exhaust tube under Merc Repair forum. Don't want to hijack this post.<br /><br />Is recommended impeller replacement determined by age or hours of operation ? Example 10hrs/year for 10 years or 100hrs/year for 1 year. What other factors play a role in the impeller life ? <br /><br />Changing the impeller every year seems akin to replacing the tires on my truck every year just incase they might blow and cause an accident. I understand the preventative maintenance concept but replaceing a perfectly good part doesn't make sense to me. There must be signs to watch for to indicate when its time to change.

 

[roscoe]

Re: Impeller design

Running the engine/impeller dry will really shorten the lifespan of the impeller.

 

[jim dozier]

Re: Impeller design

Some engines have more marginal cooling capacities than others. If you have one with a marginal cooling capacity when everything is new, a 4 year old piece of rubber with cracked vanes with a bad set in them, may cause you some grief. You don't want to have to look for pieces of impeller that have "left the building". Murphy's Law states that they will lodge in the most damaging area that is hardest to remove. Some engines have more "room" in their cooling capacities and will work better with old pumps putting out less than "new" water flow. Some people can smoke cigarettes for years and not get cancer but that doesn't mean its a good idea.

 

[Chinewalker]

Re: Impeller design

Some of it has to do with where you live and how you use your motor. If you live in a salty or silty area, it's a good idea to replace it more frequently than if you're in a clear/fresh water area. Saltwater motors LIKE to be taken apart from time to time, as it allows one to keep the bolts from becoming one with the motor. Silty motors tend to chew up the pumps with sand and grit. I generally don't go more than 4 seasons on a pump (fresh, clear water area), but I've got some oldies that get less than regular use that I've let go longer than that....<br />- Scott

 

[Vlad D Impeller]

Re: Impeller design

Any thoughts on how a titainum impeller would perform?

 

[jim dozier]

Re: Impeller design

If its metal, titanium, stainless steel, or whatever, it either has to be a positive displacement or centrifugal. And as has been mentioned in the posts above there have been problems with both. The rubber ones are positive displacement at low speeds and centrifugal at higher speeds.

 

[Scali]

Re: Impeller design

also the rubber ones vanes flex @ higher RPM's hence creating a better flow & cooling

 

[geaz]

Re: Impeller design

what about having a cooling system that did not come from the water it sat in...like a car but just made to fit marine applications...should at least be a possibility on the 4 strokes.. but i know nthing so that's my -2 cents. it air coolong a possibility, fans or something for low speeds. just something to make me worry so much about my motor overheating. with my car, the radiator blows, or i hear it boiling or there's steam. don't just have to rely on guages that could be wrong. with a outboard...it's already to late after that.