Impeller Longevity

[Gary Mc]

I know this is a 4 year old thread but it fits perfectly with some thing I have been concerned about.
My dock mate has a mid 80s Yanmar 2GMF just like mine. Last year his recirculating water pump, the one with the metal impeller failed.

The bearing had disintegrated and destroyed the pump.A new pump from Yanmar was $600 cnd!
It would be much cheaper to rebuild this pump and install a new bearing before it fails and damage's the shaft etc.
Is this a fairly common failure? It seems like replacing a 35 year old bearing would make sense.
I did the fresh water pump using an $85 dollar kit from Yanmar. it worked much better after that.
This is what it looked like.

[kmacdonald]

I used the search function with "impeller life" and it brought me here.

[Dockhead]

Originally Posted by kmacdonald

I used the search function with "impeller life" and it brought me here.

Cheers. There's nothing wrong with reviving old threads, when they are still relevant.

[Dockhead]

Originally Posted by Gary Mc

I know this is a 4 year old thread but it fits perfectly with some thing I have been concerned about.
My dock mate has a mid 80s Yanmar 2GMF just like mine. Last year his recirculating water pump, the one with the metal impeller failed.

The bearing had disintegrated and destroyed the pump.A new pump from Yanmar was $600 cnd!
It would be much cheaper to rebuild this pump and install a new bearing before it fails and damage's the shaft etc.
Is this a fairly common failure? It seems like replacing a 35 year old bearing would make sense.
I did the fresh water pump using an $85 dollar kit from Yanmar. it worked much better after that.
This is what it looked like.

Those are fresh water pumps -- a very different animal.


I carry spares of those for both main and generator. I would not mess with rebuilding them, personally -- you can get aftermarket fresh water pumps pumps for reasonable cost.

[Compass790]

Berth neighbour has had his impeller in for over 7 years, Probably does about 100 hrs per year. Our current one has done about 400 hrs but I have a strainer after the pump to sieve out vanes if it busts. Probably better to replace on schedule though.They can fail at awkward times.

[kmacdonald]

Originally Posted by kmacdonald

My 2 and a half year old Kubota with Jabsco raw water pump has 720 hours on it and no sign of any problem. I'm just starting to think of replacing it. Maybe next year.

It has 840 hours now and no sign of any problem. I'm going to hold off on changing it.

[wingssail]

It's long been my practice to change the raw water pump impellor only when the flow becomes noticeably reduced (actually when we can hear the reduced "whoosh" in the exhaust).

I know this will be looked upon as bad maintenance habits, but there it is.

However, we've often found when we changed the impellors that the pump was working (keeping the engine cool) even with most of the blades gone. Once I found only one blade left on the impellor (out of 12) yet the motor was still running at normal temp.

This on our cruise we thought the sound and the flow was indicating an impellor problem. I changed the impellor. It was actually OK, a few cracks but all blades still there. I don't mind that we did it, because I checked my maintenance log and found that I'd last changed it in 2017, 1200 hours ago! That seems long enough. (I believe that the water flow changed because I modified the intake screen during the last haulout)

In fact looking back 18 years I see that the hours between impellor changes have varied from 325 hours to the most recent, 1200 hours. The average has been 600 hours, about every 3 years.

I have never burned one up by running it dry. I only close the through hull when I'm going to be gone, and I've always remembered to open it. And the "whoosh" I mentioned is so prominent that we are instantly aware of it if it is absent (as when something blocks the intake).

Lucky us, I guess.

BTW, I know where to find the "lost" blades, and I always count them and match the pieces to make sure I have them all.

[Dockhead]

Originally Posted by wingssail

It's long been my practice to change the raw water pump impellor only when the flow becomes noticeably reduced (actually when we can hear the reduced "whoosh" in the exhaust).

I know this will be looked upon as bad maintenance habits, but there it is.

However, we've often found when we changed the impellors that the pump was working (keeping the engine cool) even with most of the blades gone. Once I found only one blade left on the impellor (out of 12) yet the motor was still running at normal temp.

This on our cruise we thought the sound and the flow was indicating an impellor problem. I changed the impellor. It was actually OK, a few cracks but all blades still there. I don't mind that we did it, because I checked my maintenance log and found that I'd last changed it in 2017, 1200 hours ago! That seems long enough. (I believe that the water flow changed because I modified the intake screen during the last haulout)

In fact looking back 18 years I see that the hours between impellor changes have varied from 325 hours to the most recent, 1200 hours. The average has been 600 hours, about every 3 years.

I have never burned one up by running it dry. I only close the through hull when I'm going to be gone, and I've always remembered to open it. And the "whoosh" I mentioned is so prominent that we are instantly aware of it if it is absent (as when something blocks the intake).

Lucky us, I guess.

BTW, I know where to find the "lost" blades, and I always count them and match the pieces to make sure I have them all.

Another impeller slacker here. My father taught me to change them every year, like clockwork.

I accumulated like that a box of immaculate impellers. Yanmar says 750 hours. Now I'm doing every 2 or 2 1/2 years, generally 300 or 400 hours,, and the old impellers are still immaculate.

YMMV. I think a big role in impeller life is played by whether or not the raw water pump is below the waterline. My main engine pump is, so it never starts up dry. My genset, on the other hand, is above the waterline, and the impeller explodes immediately if I forget to open the seacock. That one I change every year if I get through a year without a seacock accident I'm clearly more forgetful than Wingsail and my exhausts both have underwater drains, so no 'whoosh' for checking water flow.

[Joli]

We replace annually. The engine is about 20 years old with 800 hours. So I guess we change them every 40 hours? We did have the fresh water pump fail with 700 hours on the engine, the shaft broke in two.

[kmacdonald]

I finally changed the impeller in my Jabsco raw water pump. It had 1040 hours on the pump and impeller. All fins were still there but there was some cracking at the base of the fins. There was also some visible wear at the tips of the fins. The book suggests changing at 500 hours but 750 wouldn't be a problem I don't think. Keep in mind it was the original impeller in the new pump. A replacement impeller in slightly worn pump may not last as long. There were no pump seal leaks.

[Jim Cate]

A replacement impeller in slightly worn pump may not last as long.

Seems like with a worn cam the vanes don't flex quite as far, so maybe it would last longer than a new one? I dunno!

We've found that a change at around 1000 hours has avoided vane loss, FWIW (Johnson pump)

Jim

[Fore and Aft]

A client of mine told me last week he got 1007 hours out of his last impellor fitted to a Yanmar diesel.
Cheers

[rslifkin]

Originally Posted by Jim Cate

Seems like with a worn cam the vanes don't flex quite as far, so maybe it would last longer than a new one? I dunno!

We've found that a change at around 1000 hours has avoided vane loss, FWIW (Johnson pump)

Jim

If the typical failure mode is vane loss, then yes, a worn cam will likely give slightly longer impeller life. But if it's just the impeller getting stiff, wearing on the edges and losing the ability to prime, it probably won't matter. And if there are any grooves worn into the pump housing, I'd expect the impeller to wear faster and possibly have priming problems.

[Bycrick]

Once I had on hand a $3 digital thermometer. Rather than store it, I installed it on the exhaust elbow of my Westerbeke Genset. Over a several year period, I discovered that this was an almost exquisitely sensitive measurement. I could easily tell whether the sea water temperature had changed. A single cracked vane in the pump would produce a several tenths of a degree rise in temperature at the exhaust elbow. Next to oil pressure, it turned out to be the most useful measurement on the motor.

You can’t really tell the "age" of the impeller. If they’ve been sitting on the dealer's shelf, or in your spare parts stock, for a few years, they’re old before you ever install them.