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Old 26-08-2010, 02:31   #1
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Impeller Lifespan ?

Hi,
Is there any rule of thumb as to how often the impeller in a saltwater cooling pump should be changed?
I don't want to make work for myself, but I don't want it to fail either as we run in and out of a fairly dodgy entrance.
The impeller on our Yanmar has been there for at least ten years ( not a lot of hours running though) but seems to be pumping fine.
There is not much point in inspecting it, as if I go that far, then might as well change it.
Should I change it, or should there be more life in it?
If impeller life is just a lotttery I will leave it but otherwise it will get changed.
Regards, Richard.
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Old 26-08-2010, 02:48   #2
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Yes!

I have been told all sorts of bull twaddle about impellors including they need to be changed every 150 hours - thats twice as often as oil!!!

The Yanmar book says 1,000 hours and thats fine by me


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Old 26-08-2010, 05:12   #3
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Thanks Mark, looks like it has some time to go yet! Regards, Richard.
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Old 26-08-2010, 05:39   #4
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Perkins reccomends the earlier of 12 months or 100 hours. I seem to recall the owners manual for the 2GM20F we installed in our old boat in 1986 had a similar instruction. We have had difficulty when not observing these guidelines.

FWIW...
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Old 26-08-2010, 06:15   #5
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Richard, as Mark points out 150 hours would be a season for us and thats not happening. However you have had a good run at 10 years and I would be tempted to change it because whilst engine hours will have an effect it is also subjected to salt water which if dries leaves sharp crystals of salt behind. We did ours last winter after owning the boat for 3 years but I don't know how long it had been there before that. I found an older used spare on board and ditched that as well. I will happily carry a spare, but want a new spare and gasket should the need to change ever arise.

The other point to think about is what happens if a blade breaks off. Not had that problem on a yacht engine, but watched a friend strip and rebuild a 200hp V6 Yamaha outboard 3 times trying to find the water gallery that was blocked and causing the engine to over heat after the impellor broke up.

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Old 26-08-2010, 06:31   #6
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Those little rubber guys get stiff and worn after a while. I wouln't let one go 10 years. I dont change mine every year either, but I've had them come out in pieces. Change it now, It's not as hard as it sounds.
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Old 26-08-2010, 06:35   #7
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Impellers are considered "consumable" items, just like an oil filter. I've seen them last a long time and also seen them die a short, self destructing death. Having employed a specially equipped shop vac (flexible, skinny wand) to fish out the remaining bits in coolant passageways, many times, it's just best to accept a simple set of rules on them. Change once a year regardless of how few hours are on them and 150 to 200 hours in regular, pleasure craft service. I've seen impellers fail that had 10 hours on them, because they sat, unused in an boat, for a number of years prior.
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Old 26-08-2010, 06:36   #8
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Having worked in boat yards and replaced MANY impellers with under 200 hours use that were missing one or many vanes, yet still "pumping" I now change every spring regardless of visible condition.

For the $17.00 and ten minutes I don't even second guess it. Engines replacements are 15k+ jobs these days and an impeller is less than an oil change for me.

Just replaced one last week with 166 hours use;

"It's pumping fine but I have a little steam and I know you told me steam was not good."

"Did you leave it in over the winter with the glycol?"

"Yes I forgot to pull it out."

"Have you plugged the raw water strainer this season?"

"No, just a little eel grass."

Well, that impeller was missing three vanes and instead of a simple $23.00 part, and ten minutes, it required an R&R of the hoses, HX and HX end caps which turned an $80.00 service call into a $300.00 service call. Found all three vanes but it cost him. A LOT more than changing it in the spring, or removing it in the winter and re-installing it in the spring.

I have seen them go a long time "still pumping" but often not cooling the engine well as flow was reduced. I have even seen pumps with only two vanes left still moving water, not much but still moving it.

Some Yanmar's can take as much as 30 minutes but on most engines this is a 10-15 minute job max. If you buy your impellers from the pump makers, not the engine manufacturers, they are a LOT less money..

For my engine my cost on the Johnson 810-B1 impeller is abut $17.00. The SAME impeller from Westerbeke is $40.00. For the cost of a twelve pack of decent beer I think I'll take the ten minutes and change it yearly..
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Old 26-08-2010, 06:41   #9
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My Yanmar book also says 1000 hours, so I let the first ones go 6 years before hitting that mark. One came out intact and the other had two blades missing. Next spring will be 3 years so I plan to change them then. I'll have less than 500 hours on them, but I would rather not have to pick impeller parts out of my heat exchanger. Depending on your engine it may be more trouble than you think. I decided to have my first change done by a professional and the first thing he did was pull the starters off my Yanmar 3JH3CE's. I would have struggled for hours trying to get them apart without doing that. There's not enough room to get the impeller puller between the starter and the pump on that engine. Removing 3 bolts is quick and much easier than struggling to get the thing out without doing that. Watch and learn.
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Old 26-08-2010, 06:45   #10
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In my experience, the environment the pump is located makes a difference. I have 3 engines that all use the same impeller. My genset sits ~20" above the water line, hence that pump works harder, whereas my main engines straddle the water line and the raw water pump is situated below the water line. I've gotten ~900 hours from impellers on the main engines and have replaced the genset impeller twice in 400 hours. I also have a check valve on the genset raw water hose.

In addition, if you let the engine sit for a long time (months), you'll notice not only more frequent impeller failure, but the lip seals will fail faster as well.
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Old 26-08-2010, 06:47   #11
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If you are changing the impeller at 1000 hours just because, I would change the lip seal also.
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Old 26-08-2010, 12:04   #12
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Quote:
Originally Posted by Captain Bill View Post
My Yanmar book also says 1000 hours, so I let the first ones go 6 years before hitting that mark. ...
My 4JH4 manual states:
1. Check earlier of every 250 hours and 1 year
2. Replace earlier of every 1000 hours and 4 years
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Old 26-08-2010, 12:41   #13
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Ahh, yes, some good points on how much you use the engine. Sea Life knocks over 1,000 hours in a year.

And we did 168 hours in one week a few months ago..... How many hours in a week?

Now we have the solar panels the engine stays in a happy state of "off" much more often!

I guess if its time based I will be doing mine every year
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Old 26-08-2010, 13:25   #14
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As many have said above, both time sitting unused and engine hours will eventually diminish the supple nature of the impellor blades, but other factors can cause even a new impellor to fail. For example, if you raise your anchor in the typical coral marl bottom of much of the Florida Keys or Bahamas and motor over the cloud of sediment before it settles, this course grit will quickley chew up an impellor. Another quick demise of an impellor would be when backing off a soft grounding and kicking up a lot of bottom sediment into your raw water intake. I tend to change my impellor on my Yanmar every 1,000 hours or two years, but I'm keeping an eye on my water temperature and uneasy about my impellor condition if I've motored through stirred up bottom sediments. Take care and joy, Aythya crew
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Old 26-08-2010, 19:00   #15
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Thanks everybody for your input. I will err on the side of caution and change the impeller.Have done it a number of times before. On the Yanmar 3JH is is a bit of a nuisance as you have to drop the starter first which is not a good design feature!
Regards, Richard.
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