Impeller Best Practices

Thought this deserved a separate discussion vs piggybacking on the "Stuck Impeller" thread.

Also, because these two impellers were easy to pull.

They are from the twin Lehman 135's on our Defever 44 and I discovered them this way after a 1,000-mile delivery trip from Florida to the head of the Chesapeake. I think there were 6 intact vanes on one and 5 on the other!



After seeing this and almost stroking out, I started collecting the bits of what I assume is neoprene downstream in the raw water system. You can see the debris from one of the damaged impellers below, alongside an intact impeller.



I learned a few things:

First, the Ford Lehman 135 must be one tough engine. Both engines were monitored routinely throughout the trip by a highly respected delivery skipper--via the temp gauges and regular direct infrared thermometer readings--and they never overheated. The exhausts were also checked hourly and no reductions in water flow were discernible. This was especially surprising after I found most of the neoprene pieces up against the tube bundles in the heat exchangers.

Secondly, I will never start a long cruise without new, or lightly used, impellers. The ones that came with the boat were likely rotated in and out of use to extend their service life.

Third, I'll probably chuck out impellers I replace even if they're intact rather than try to eek a few more months out of them. (I have already pulled them while the boat's laid up for the winter.)

Lastly, I'll check the impellers physically before, during and after trips. It was my bad that I assumed they were up to the trip . The new Speed Seal covers I just installed on the impeller housings should make that less of a chore.

If anybody has a better approach to impeller health, please share.

Better lucky than smart, I guess.

I've seen this countless times. Few blades left on an impeller and the engine doesn't even run warm at cruise rpm. Each time it confirms two things to for me, 1 the "Lehman's are prone to over heating" statement I hear from time to time is an urban myth. And #2, it's good to run your engine up towards full rpm once in a while and leave it there for a few minutes or so to see if the temps climb indicating a possible water flow issue.

I think checking impellers before every trip to be a bit extreme - especially considering how many other items could also bring one's trip to a quick stop. For example, how are the many hoses and clamps on the engines? How about the oil cooler hoses? Most owners don't touch these but they all have definite lives and a failure in any one could cause serious problems and/or engine damage quickly.

I think if one has "recent" impellers that have not be on the shelf for years, and some spares, you should be able to expect at east a couple hundred hours from them (and often much more). Impellers don't usually fail catastrophically and a yearly change is usually sufficient for most types of use.

Fortunately, the impeller "bits" are an irregular shape and so won't easily block the flow into a tube. Still, it IS amazing that those impellers were as bad as that and the engines operated normally.

I think the advice about bringing the engines up to full power occasionally is a good tip. My situation is a perfect example. I had one engine that would always run 10 degrees hotter than normal if pushed above 2000 rpms where the other did not. This winter I have completely gone through the cooling system and found the main engine heat exchanger on that side defectively built! These engines have 2 pass exchangers. At one end is a "separator" plate which forces the water to go up half the bundle one way and come back in the other half. Well on this particular heat exchanger that plate had NEVER been soldered to the sides OR the end plate that holds the tubes. This left about a 1/8" gap which I calculated at 7" long. Some of the raw water flow in/out could simply shortcut the path completely and not go down ANY of the tubes. I calculated that approximately 20% of the raw water flow would simply bypass through the exchanger and not provide ANY cooling. The amazing part is that this exchanger had been in the boat at least 9 years and the engine never overheated. But the clue was how it always heated up a bit at higher rpm as opposed to the other one. Considering its age, I replaced that exchanger with a new one and will keep it as a "get home" spare.

Ken

We change impellers yearly during our spring routine maintenance work. So they run ~ 200 h. We don't reinstall them regardless whether they look o.k. or not.



best regards / med venlig hilsen
wadden

MY solution has been to install Y strainers in line after the impeller pump.

This will catch all pieces and not restrict the water flow.

It is also quick to check if you think the sea cock or intake strainer is plugged.

Sendure makes excellent bronze units.

My guess is much impeller damage is caused by sitting....and dry starts.

I get easily 4 to 8 hundred hours out of my and assistance boat impellers..even in incredibly sandy conditions on the tow boat.

That's based on around 400 to 500 hrs per year...the impellers look great and are pumping with no temp issues.

My FL120 shut down last week on my way to the Bimini. 100% blockage of the strainer. The impeller was not damaged and looked fine after 1,100 hours.

Just out of curiosity what blocked your strainer so completely?

waddenkruiser said:

We change impellers yearly during our spring routine maintenance work. So they run ~ 200 h. We don't reinstall them regardless whether they look o.k. or not. best regards / med venlig hilsen wadden

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We also change/replace annually, on our schedule.

We had gone through a large patch of fine sea grass. The strainer was full and the seacock was jammed with grass. It took a good but of time to clear all the blockage. It didn't leave us enough time to get to Bimini before sunset do we came back to Miami.

I've been in the marine engine business for almost 20yrs. I understand just about everything about these beasts- except trying to understand impeller life. I have seen impellers at least 10yrs old with lots of sitting time- look perfect. I have seen others coming apart after 100hrs with very little sitting time.

A few patterns are noted: The Jabsco's on Detroits seem to last forever. Sherwood impellers on Cummins don't. Mine included. Not only is the pump arguably a POS, but the impeller on mine likes to load the aftercooler with vanes even with little sitting time.

Mine can go 200hrs, I change the AC zinc and there are vanes. Hmm, where did they come from??!! Change impeller, yep in rough shape. Go another 200hrs, no vanes in AC. Go another 200, no vanes, ok. Get ready for long trip, put new impeller in just to be sure. Old one has 400hrs, looks great. Go on trip, put about 200hrs on new imp, change zinc on AC. Vanes in there. Great. 200hr imp coming apart!! Get p'd, put the 400hr imp back in. I think I have put another 400 on it, so now about 800 total. Checked aftercooler, no vanes.

Getting ready for another trip. So roll the dice and run on the 800hr one, or roll the dice and put a new but iffy one in???

These are all new impellers in factory Sherwood packing, bought from same vendor.

Go figure.

They last forever until they don't.

My experience from the east coast where there is shallow water and sand is that some boats and how they are used will suck sand and destroy impellers in no time. Here in the NW impellers seem to last a lot longer. One grounding or near grounding in sand with motor use to get off and its time to check your impeller.

Not sure sand destroys them...though it wears wear plates and pump bodies.

I probably put 50 hrs a year 2 feet of sand slurry as I pull boats off of sand bars.

I still get 500 to 1000 hrs on impellers.....sometimes more.

Once I wore a hole in the pump body and ran around for several days that way till it was located and a new pump put on.

I guess I have to agree with Ski more than anything.....no rhyme or reason why some impellers or pumps just don't last.

I found some interesting information in my shop manual for the Yanmar 4JH3E which uses a Johnson pump. The owner's manual calls for impeller inspection annually or 600 hours. The repair manual pump specifications indicate the design durability for the impeller is 1500hr minimum. I replace annually and do not re-use the old impellers. I keep one backup aboard and use it for the replacement so that the backup is always relatively fresh.

Johnson now uses "a new impeller compound MC97 which has also resulted in an extended service life of the impeller compared to impellers in Neoprene." Nitryl is only recommended where the pump will encounter oil.

FWIW, many Johnson impellers have Jabsco equivalents so there might be some interchangeability with other pumps and engines. I have heard some mechanics state that Johnson impellers are more durable, but that is only here say.

psneeld said:

I probably put 50 hrs a year 2 feet of sand slurry as I pull boats off of sand bars.

I still get 500 to 1000 hrs on impellers.....sometimes more.

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You've said before the assistance boat is powered by a 454 gasser. Out of curiosity which pump and impeller do you run on that boat? I have a Jabsco on my 350.

That's interesting, Larry. I switched from neoprene to nitrile 300 hrs ago. I used to change theneoprene then nitrile impellers every 200 hrs, but went longer this last time b/c the nitrile still looked like new on the last 2 changes. This time at 300 hrs, my impellers still worked and looked great, but I still replaced them.

I just looked at what I put in my pumps this week. I learned that I messed up and bought the neoprene impellers by mistake. They're already in there so they can stay for the next 200 hrs, then I'll replace them with nitrile impellers for the next 300 hrs.

Now that I have SS knurled head allen screws in the pump plates instead of the standard screwdriver screws, the job is much easier. I can now replace both impellers in about a half hour if I don't remove the salon carpet and hatches. That's a huge improvement over my previous experiences.

CPseudonym said:

You've said before the assistance boat is powered by a 454 gasser. Out of curiosity which pump and impeller do you run on that boat? I have a Jabsco on my 350.

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Not quite sure...in FL instead of near my boat ....thankfully!!!!!!!! !

Pretty sure it is a typical Jabsco that bolts to the front of the crankshaft...nothing unusual about it.

just another example that there are too many worriers on the forum that need more practical experience.

psneeld said:

just another example that there are too many worriers on the forum that need more practical experience.

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Until some of us attain your level of experience, is it still OK to ask questions?

angus99 said:

Until some of us attain your level of experience, is it still OK to ask questions?

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Asking is fine...even my experience is limited compared to guys like Ski and some others..

People post what they feel comfortable with and that's OK too.....but some think that a few hundred hours a year on one or two boats is a "range" of experience....not!

angus99 said:

Until some of us attain your level of experience, is it still OK to ask questions?

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Many of us have less experience than some and some of us sound like we have all the answers when we don't.

I come to this forum for different perspectives on solving a problem:

1. Sound advice from those with much more experience than I have

2. Innovative ideas from those who think outside the mainstream box.

They are the folks I listen to, not those always banging their chest to reemphasize the importance of their presence here.

Many here try to provide lessons learned for our own stage in the learning process so others don't repeat our mistakes. Don't be bothered by the minority who poke holes in others while they prop themselves up for others to admire.

I appreciate your contributions and interest in sharing the passion we all experience on the water.

meridian said:

We had gone through a large patch of fine sea grass. The strainer was full and the seacock was jammed with grass. It took a good but of time to clear all the blockage. It didn't leave us enough time to get to Bimini before sunset do we came back to Miami.

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Interesting. I've only seen that happen at anchor with genset and A/C strainers, never underway to engine strainers. Usually when underway the grass just gets pushed aside and with the inlet for the engine strainer being several feet underwater not much grass finds its way in there. First time for everything I guess. Thanks for sharing.

Looked at the SpeedSeal website and that and the Speedseal Life look like pretty good products.

ktdtx said:

Looked at the SpeedSeal website and that and the Speedseal Life look like pretty good products.

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Our boat came with SpeedSeals on the mains and they're a great improvement over the stock impeller covers. Four large knurled thumbscrews instead of the usual 6 or 8 micro screws. Nice O-ring seal vs the flimsy paper gasket. Heavy-duty cover plate that puts strong, even pressure on the O-ring. Makes hanging over the starboard engine to swap impellers a much easier task. All in all, a well designed product IMHO.

(Correction to my original post for any careful readers out there: I did not install these; the PO did. Not sure where that thought came from.)

Capt.Bill11 said:

Interesting. I've only seen that happen at anchor with genset and A/C strainers, never underway to engine strainers. Usually when underway the grass just gets pushed aside and with the inlet for the engine strainer being several feet underwater not much grass finds its way in there. First time for everything I guess. Thanks for sharing.

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A few months ago my neighbors boat here at the Marina was put back in at Yacht services at to low of a tide, they wait for the tide to come up to start the egines but the mud sand and a little grass had been pushed into one of the intake it destroyed one of the impellers

But like you have never seen it underway but would normally be me to do it first

Yeah I could see that happening at that yard. Very shallow there.

On a side note, it's sad seeing what that yard has become knowing its previous history.

This thread prompted me to change the impeller on my Starboard CAT engine. My log indicates that it has about 1,000 hours on it after traveling the east coast from CT to FL for the past 2-years. Roughly 250 hours each way including some side trips. I was pleased to find the impeller in virtually new condition. Not a tear, crack, or deformation anywhere.

I replaced it with a new one and will keep the old as a spare. I will not change the port engine impeller as that pump was rebuilt last year. In researching impeller pullers, I found this information on the Seaboard Marine website thought it might be of interest:

Tricks & Tips to extract an Impeller


This is something that should and needs to be done with ALL impellers when you are removing them... Once the cover plate is removed, you need to spray WD-40 (or something similar) inside the housing and into the spline or key & shaft area (liberally) and then BUMP the engine. Then spray it one more time and bump the engine again... TWO times and now that impeller is ready to be removed.

Once you do that, it will "break" the dry bond that always seems to occur between the rubber and the housing and also loosen up the spline (or key). This is essential during any impeller removal and now the impeller will slide out EASILY.

When installing a new impeller, throw out all that crap about lubing - Use any common white lithium grease (or similar grease) and life becomes easy for all� Instant prime too. Be sloppy with it, coat all inside, shaft and impeller and I personally guarantee it with not hurt your impeller if you are planning to finish the job and test the engine within a few days or so... That old wives' tale has got to go - But, if this makes you squeamish, then go ahead and use a synthetic or silicone based grease made specifically for all types of rubber elastomers.

Also, all that crap about which way the vanes have to go is also just that - TOTAL CRAP... It makes ZERO difference as the split second the engine cranks, the blades will flip as needed. But of course, after any impeller replacement, do a test and check for leaks, etc.

Happy Fishin'����Tony

I ran a pair of sherwoods on Cummins for years in a low time sandy water situation. Rarely lost a vane but often had seal failures leading to bearing failures and leaks.


The seals just don't seem to like to sit.

What happens on the Cummins P17XX Sherwoods is that the carbon/ceramic face seal bonds while sitting. Then when rotated, the face seal stays bonded and the shaft spins inside the seal, where it should not. Then that wears things and it leaks there. On machines that don't sit long, the pumps are fine.

They have upgraded these pumps a few times. I don't know if they actually fixed the issue, but new ones I've installed have not had problems.

When changing the impeller, look at snap ring holding seal washer in place. If snap ring has polished the washer surface, shaft is spinning in seal and seal is not long for this world.

Replaced Impeller, need to prime pump

I have a Hirshine 37, with twin Watermota Sealion 120s. Using the boat the other day, the port engine died! It was running hot, smoke and the smell of burning rubber. I thought the worst, Oh no new engine!... The next day, i used a 24" bar with a socket on the crank, it moved freely. I thought okay, I dont need to repalce the engine. It started fine, no water coming out of the exhaust. Okay must be water pump. The impeller was completely shot! No splines on it at all. So, it was replaced. Now, I have to prime the pump.... Anyone have any suggestion as to how I force sea water back into the raw water pump?

Ours primes by itself since the impeller is below the waterline. Are you sure yours isn’t self priming? Crack the impeller cover plate with the seacock open and see if water comes out.