Engine impeller change frequency

I seem to recall discussions from time to time regarding the frequency of raw water pump impeller changes, but could not readily locate a thread on it.

For my starboard engine I have changed the raw water pump at 2 or 3 year intervals due to failed seals, and thus changed the impeller.

Yesterday, during a 2000 hr engine service when we did a lot of things 'whether they needed to be changed or not', we changed the port engine impeller. Its raw water pump seals had not leaked, and since the engine was always at normal temp I had not checked or replaced the impeller.

So the mechanic was just as curious as I was to see what it would look like after 7.5 years and 2000 hrs of use. The pic is below. Sure, one vane was gone but otherwise it was working fine. But we changed it anyway!

I try to change mine every 3 years. They look almost new but do have a set to them. I would do it more often than 7+ years.

I pull my impellers at least once a year because I don't want them to come apart. I change the Detroit impellers at about 5 years. Generators a little sooner. If they have any cracks I change them.

Comodave said:

I try to change mine every 3 years. They look almost new but do have a set to them. I would do it more often than 7+ years.

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I will likely do it more often in future. But if getting water flow from the exhaust and normal engine temps then perhaps checking rather than changing might be ok. I suspect I'll get seal failures way less than 7+ years in future. The seal failure for the other engine averages 2.5 years.

Gotta find those pieces!!! Blow back through the cooler!!!
On my NL gen., replaced the impeller because of failure. Blow back, MANY pieces. Perhaps the PO just replaced the impeller and never did the 'blow back' procedure. Way too many small pieces to come from only one impeller IMO

I saw or heard, replace impellers annually, saving the one you took out for an emergency spare, if it looks good.

OldDan1943 said:

Gotta find those pieces!!! Blow back through the cooler!!!
On my NL gen., replaced the impeller because of failure. Blow back, MANY pieces. Perhaps the PO just replaced the impeller and never did the 'blow back' procedure. Way too many small pieces to come from only one impeller IMO

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Yes of course!

I did not fully explain. Part of the 2000 hr service was a barnacle buster flush of the heat exchangers, after which the HX end caps were removed, and replaced after a B Buster bath. As well as the impeller piece, and it pretty much was just one large piece there were a couple of bits of anode that had broken off when I was doing periodic checking of them.

I had tended to replace anodes after 2/3 was gone. But this meant that they were a bit crumbly or scaled up to a greater diameter than the threaded hole in the HX. Going forward I will be replacing anodes earlier, say once they are half gone.

Where I boat anodes last quite a long time, and when just buying the pencils to fit to the brass plugs the cost of early replacement is not that great. It will be better to have early replacement than to have pieces of broken anode in the end cap area where smaller pieces could subsequently block a HX tube.

We run 200 hours +/- per year and change annually. I’ve got quite a few spares as a result but better safe etc. Cummins 5.9bta, 330 HP.

I change every 2 - 3 years. If I go too long, I end up doing an emergency change during winterizing, as a slightly weak impeller will still seem to work fine until you feed it an air bubble while trying to pour antifreeze fast enough. Then it loses prime and that's that.

I usually change every 2 seasons. They always look fine. I never keep an old one for a spare. I buy a replacement for the new one I just installed.
Knock on wood in 30 years of boating I have never had to flush out pieces of impeller.

Every two to three years of moderate usage. I don't know if salt is bad for impellers but since it's bad for everything else I assume it is not a friend of impellers. I am in fresh water, which is generally pretty cold, don't know if that has any effect either.

pete

Every Feb during the annual service (by the mechanic).

Impellers work well, until they don't. I would not be comfortable running the boat with pieces of impeller vane partially blocking flow through the heat exchangers. We regularly run WOT and want the cooling functioning as designed.

Impellers are not expensive and, for most, changing is a DIY maintenance project. So for peace of mind I follow manufacturers recommendations:
-John Deere: 500 hours or annually, whichever comes first
-Northern Lights: 1000 hours or annually, whichever comes first

Do you remove your impellers in the winter if you are on the hard?

OldDan1943 said:

Do you remove your impellers in the winter if you are on the hard?

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Personally, I don't. Never heard of a good reason to. The antifreeze provides enough lube to keep them from sticking while sitting idle in the pumps and tearing on startup. Plus, on my engines, I have to pull the pumps to split them and get the impellers out, so if I were going to do that, I'd just change them every year.

Every year I replace impellers. 250-300 hours per year put on the engines. Have been told I could push to every other year but I simply like to avoid issues and err on the side of proactive maintenance.

I believe it is Ted (O C Diver) that added a strainer between his raw-water pump and heat exchanger. His set up is designed to catch broken pieces of impeller before migrating to the heat exchanger, etc. Ted?

Giggitoni said:

I believe it is Ted (O C Diver) that added a strainer between his raw-water pump and heat exchanger. His set up is designed to catch broken pieces of impeller before migrating to the heat exchanger, etc. Ted?

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I did that recently based on Ted's photo. Full project writeup here: Raw Water Impeller Strainer

We do ours annually on our schedule. Having a single, it’s not worth the risk for a 15 minute job plus I like working in a cool engine room while tied to the dock.

boathealer said:

I did that recently based on Ted's photo. Full project writeup here: Raw Water Impeller Strainer

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You and Ted are valuable assets to TF! You guys have designed my next project.

I've upgraded the original Sherwood seawater pump on our Cummins 6BTA 5.9 M3 to a Seaboard Marine SMX 1730 pump. Replaced the impeller every two years and 1600 hours. So far (two replacements) it has always looked OK. Thinking I might go to annually.

boathealer said:

I did that recently based on Ted's photo. Full project writeup here: Raw Water Impeller Strainer

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Excellent post! Thanks!!!

Mr Insequent,
This was my post on the thread you referenced:

Aboard Salty, I have spare RW pumps for each JD main and the generator. I rebuild the pumps (new seals and gaskets) as soon as I swap them out, and store them with a new impeller ready to install. I can swap out the entire pump as quickly as installing an impeller in situ. Also, the new seals only cost a couple bucks, and are cheap insurance against the inevitable.

We boat year round down here, so I usually swap out the pumps at 2 years.

I use plain, fresh stock impellers...never saw the need for the high$$ impellers.

Changed my impeller yesterday. I also have the Cummins 6BTA 330 hp and changed over to the SMX 1730 pump a few years ago. Nice pump, definitely better built compared to the Sherwood (stock one). The old impeller had 2 years of use, and almost 500 hours on it. On close examination, the old impeller looked "almost new".

During the winter, I don't use the boat. I store the engine with a mixture of freshwater and "salt away" in the raw water system. The local dock water is shut off to prevent freezing, so if I want to keep the saltwater out of my system, no running of the engine during the winter down time. So, I "bump" the starter every month to move the impeller to prevent it taking a set. This seems to be working??
I think I probably could go 3 years if I removed the pump cover annually to visually inspect the impeller condition. However, being somewhat conservative, I think I will do the annual inspection and stick to the 2 year interval.
Richard C., how long do you think (hours) before the pump might need a rebuild or are you going to wait for a visual signal (like a leak)?

I replace our impellers annually at the start of the season. At $22 each, and an easy job, its a no brainer for me.

Ken

Geez Ken,
My one impeller (basically same price for SMX brand or Sherwood equivalent) cost over $100!!
I know, not that bad on the scale of boat costs

Even well maintained impellers can fail with out warning and dump chunks of impeller in the system.

The only cure I know of is a Y strainer of the right size to collect the chunks etc after the pump..

Not very expensive , and if there is a cooling problem its only a few seconds to check the mesh basket rather than anything else.

Good points FF. Ted has suggested the strainer as well. Even though it adds another potential leak point (2 hose clamps and the strainer basket itself), if you have the room for it, the strainer does make sense should you suffer any kind of impeller damage.

FF said:

Even well maintained impellers can fail with out warning and dump chunks of impeller in the system.

The only cure I know of is a Y strainer of the right size to collect the chunks etc after the pump..

Not very expensive , and if there is a cooling problem its only a few seconds to check the mesh basket rather than anything else.

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Or.... on the newer popular Cummins models that end in "A", the A stand for "aftercooler"....and that is where you will find the pieces of impeller as they can't get past there.

True Baker, true.
But, disassembling the aftercooler (which really should be pressure tested when disassembled), or removing the hose and "fishing out" the small pieces through the opening, sounds like much more work than just opening a strainer and removing the bits. Now having the space to place a strainer between the raw water pump and the aftercooler can prove difficult, especially if on the Cummins 6BTA with an installed fuel cooler between the pump and aftercooler. I removed my fuel cooler and now there is probably room, so I am considering it, although so far, there has not been an impeller issue. Only takes once though.