Raw water impeller replacement - maintenance interval.

[TomF]

This topic has been covered but I would like to hear from real life experiences on how long owners have gone before having an impeller failure or maintenance replacement beyond 200 operating hours.
Yanmar manual for my 4lha-stp is not concise and only talks about inspection - Check Impeller @ 125, 250 and 1,000 hours
I generally do not travel far from my marina and with twins could limp home on one engine, but certainly do not want to experience an impeller failure. Currently I have two years and 220 hours on my raw water impellers and trying to figure out when to replace them.
Thank you for your valuable insights.

 

[tiltrider1]

I have never experienced a raw water impeller failure on a propulsion engine.

I have experienced several raw water failures on generators. I use generators very infrequently and quite irregularly which means Many of those failures were low hours but very old impellers.

I have never gone longer than 5 years on a propulsion engine before my comfort level is exceeded.

 

[O C Diver]

If you're going to do it yourself and the cost is the impeller, pick how many years you want to go and do it as a spring commissioning job. The downside side of waiting to long aside from possibly overheating the engine, is that you may have to go in the transmission cooler or heat exchanger to retrieve the broken impeller blades.

If you're paying a mechanic, there is the cost to way versus breaking down away from the dock.

When I ran my charter boat, I did it annually to avoid loosing a charter.

With the trawler I installed transparent strainers down stream to collect the impeller bits. The added advantage is that every morning when I do my engine room check, I can see if the impeller is starting to fail.

Last thing I will tell you is that all impellers aren't created equal. My OEM Johnson impellers last multiple times longer on the main engine than Sherwood impellers. But the Sherwoods do pretty well in my Onan generator.

My last Johnson impeller went well over 1,000 hours before I replaced the pump. The Sherwood impellers rarely last 400 hours in the Onan.

Ted

 

[C lectric]

I fully rebuild and inspect my pump every 4 to 5 yrs. In the meantime the impellor stays.

I put on about 150 hrs to 200 hr yearly. My engine is run at about 1,800 -2,000 revs typically.
I , to date, have never seen any sign of impending impellor failure.

I suspect a lot also depends upon the speed/rpm the pump is spun at. My engine/pump ratio is about 3.5:1 so the pump is spun relatively slowly compared to many. Have a look at that as the actual revs of the pump will have an effect on the wear and tear. A smaller pump may be spun faster to get the water flow needed.

I've had my engine for now about 35 yrs for comparison.

 

[Bacchus]

My Yanmar 6LYA impeller failed the year I bought / launched. It was 5 yrs old but only 125 hrs on it. I had ordered one but yard hadn't received it when we took off.
I have done 4 years twice now W/O any issues and impeller looked decent.
I now no more than 4 years. We are in fresh water and usually put on between 75-150 hrs / year

 

[twistedtree]

I'm a bit more cautious - perhaps more than I need to be - but it's always been worth some extra effort for increase my odds of trouble free boating.



When I hauled my boats over the winter, I always installed a new impeller in the spring, regardless of hours. After sitting in one position for 4-5 months, the impellers always held their smooshed up shape, so I replaced them.


On boats that have been used at least to some degree year-round, I have been changing them every 2 years. If I swap an impeller and it's 100% intact, I might stretch the next interval by another year. And if there is any deterioration, then I'd shorten the interval next time around. It's much easier to change an impeller than to disassemble the cooling system to fish out broken fin bits.

 

[jleonard]

I always replaced mine after 2 seasons, regardless of hours.
That covers 3 different diesels over a period of 30 years.
Never had an impeller failure.

 

[danderer]

Replaced the impeller on the main engine a few days ago because one vane was starting to tear. That impeller lasted one year and 520 hours.

On previous boats I would replace them every 2 years/200 hours. Never had a failure.

My NL generator specifies 1000 hrs - that's above my comfort level.

 

[twistedtree]

In anything other than a commercial application, I think age is by far the determining factor, not operating hours. If you pull the impeller and the fins are starting to tear or crack, you clearly waited too long.

 

[TomF]

Thanks for all the real life comments. Still not sure what to do and still confused as to why Yanmar was not more specific on a maintenance interval.

 

[C lectric]

If you are still not sure and Yanmar does not cover this properly then do it every year.
Take good note of the impeller condition at the yearly interval.

If GOOD then go for two years. Since you seem to have done the two year interval then try 3 years or simply for comfort sake stay with two years which is not bad.

Better safe than sorry and stop worrying about it.

Part of the trouble for engine mfgrs. is some owners will put on hundreds of hours yearly, some will put on only dozens of hours, if that, yearly and it makes a big difference in the impellers life. So no matter what they suggest they could be criticized.

Cooling system problems can shorten an impellors life substantially.
Both to high backpressure and vacuum from clogs or deposits buildup in hoses or hardware for whatever reason can do that.

So they make it your problem to determine the interval based on your comfort level and your useage. Best to go short and learn.

And you will not likely get a categoric opinion telling you that you can go so many years or hours.
You have already seen this with our experiences.

 

[rslifkin]

With winter storage and antifreeze to abuse the impellers, I replace mine every 2 years regardless of hours. Beyond that there's a risk of them getting too stiff to prime if they get any air during winterizing or on startup in the spring. They're normally stiff, but intact, no cracking, and still pumping fine at replacement time.

If we were on a long trip without winter storage I'd probably let them go for around 500 hours before replacement. Depending on how they look at that point I'd adjust the interval. If we ran on plane a lot, I might pull and inspect at 300 hours to decide if it's time to replace or go for 500 hours.

 

[fgarriso]

On my mains I change them every year. The impellers don't cost that much and tearing down the heat exchangers is not fun if blades break.

 

[North Baltic sea]

Hi,

I am chek every yars and now 5 yars and about 2000 hours i replacement new impeller, only just as I wanted, for no reason.

The old one was in good condition (no cracks, etc.). I leave it in case I need to change it quickly at sea, its wings are already in a good position to do the job easily.

spray silicone everywhere and in a plastic bag to wait, I hope I don't need it out at sea as an emergency aid.

the impeller is Seaboard's own, for their excellent raw water pump that replaces the poor Sherwod pump in my Cummins qsb.

NBs

 

[rgano]

I change my Yanmar 6LPA-STP impeller every 2-3 years. For generators, I have found it advisable to change the impeller annually. Can't tell you how many have failed in forty years on boating on Onan and Nextgen gennies. Just not worth the hassle to go over a year, regardless of hours.

 

[Cigatoo]

Yanmar called for replacement every 600 hours under “normal” conditions on my 4LH. IE not sucking in a lot of sand and the like. As mentioned above all impellers are not created equal. The Yanmar Impeller is a big heavy impeller. I think 600 hours could be premature. I did mine twice or 3 times over the course of 16 years 1,000 hours. They looked like new when I replaced them. No cracks or any visible wear. If the boat is new to you maybe replace it and save the old one.

 

[kchace]

When I replaced impellers (with about 1K hours on them) on my new to me boat, one impeller had lost almost all blades, the other impeller looked perfect. Both had been replaced from the same batch at the same time. Go figure.

Ken

 

[rgano]

Yanmar called for replacement every 600 hours under “normal” conditions on my 4LH. IE not sucking in a lot of sand and the like. As mentioned above all impellers are not created equal. The Yanmar Impeller is a big heavy impeller. I think 600 hours could be premature. I did mine twice or 3 times over the course of 16 years 1,000 hours. They looked like new when I replaced them. No cracks or any visible wear. If the boat is new to you maybe replace it and save the old one.

My new Yanmar impeller lasted around two years before it had a cracked blade after less than 200 hrs; thus my about 2-year interval. 600 hours would seem like a ridiculous gamble to me.

 

[Fletcher500]

Main= 2 years. It always looks fine, but I am not willing to chance it.

Gen= 1 year.

 

[twistedtree]

It's sounding like others are finding that generator impellers don't last as long as main engine impellers. I generally see this too. My generators use Jabsco pumps, and from what I have seen Jabsco has gone down the toilet along with everything else that Xylem has acquired. So I don't know if it's



1) smaller impellers don't last as long,
2) Jabsco sucks,
3) generator usage patterns make impellers die faster,
4) something else.


Any opinions?

 

[rslifkin]

My generator gets less hours than the mains, but historically, the impellers seem to last quite a while before age gets the better of them. I remember 6 - 7 years being the limit. Not a clue who made the pump for Onan though, as none of the big pump makers list one that matches it (or an impeller for it).

That said, I'm getting ready to convert the gen to an electric seawater pump at some point. The OE impellers are now discontinued, so they're getting harder to find and the available stock is just getting older and older. Another victim of Cummins buying Onan and killing off parts availability for a lot of the legacy Onan units. I tried one of the 2 aftermarket options and it blew up (lost all but one of the fins) after a year and less than 50 hours. Only thing at this point is that I have to figure out a belt tensioner for the generator, as currently the seawater pump sets the tension (and I still need the belt for the coolant pump).

 

[motion30]

Lots of post here that say depending on condition. Who pulls the water pump apart just to look at the impeller and not replace it? That seems very silly to me

 

[rslifkin]

Lots of post here that say depending on condition. Who pulls the water pump apart just to look at the impeller and not replace it? That seems very silly to me

To me that would only make sense if putting on quite a few hours in a year. A couple of inspections may be worthwhile to see how it wears and ages so you can determine a good replacement interval. Once you've figured that out, just run to the interval and replace it. Ease of pulling for inspection will also depend on the design of the water pump. For some, it's pretty quick and easy to take a look, others not so much.

 

[C lectric]

You are right about the others, NOT SO MUCH. Mine requires the pump to be removed
and although I'm sure not as bad as some , it is not an easy job to get it back in place and adjust the belts. THe belt adjustment is itself a major pain in the neck.

 

[jleonard]

So I don't know if it's
1) smaller impellers don't last as long,
2) Jabsco sucks,
3) generator usage patterns make impellers die faster,
4) something else.

Any opinions?

I never had any issues using Jabsco impellers. But I only use them 2 years, then I replace with my onboard spare, then buy a new spare.

 

[sunchaser]

My Jabsco pumps and impellers have behaved impeccably with + 2 years on impellers and they come out looking new.

But, no sand, deep clean water, don’t store on the hard, rotate the engines frequently, pumps well below the water line and the vaunted DeFever sea chest play a big part.

 

[TomF]

This is an amazing group of expierienced captains with valuable insight. For me the net is change every two years is safe and three years and beyond a gamble. The enlightment is the generator. I have a NextGen 3.5 kw with three year old impeller and that one I will change now. Safe boating .

 

[Don L]

This topic has been covered but I would like to hear from real life experiences on how long owners have gone before having an impeller failure or maintenance replacement beyond 200 operating hours.
Yanmar manual for my 4lha-stp is not concise and only talks about inspection - Check Impeller @ 125, 250 and 1,000 hours
I generally do not travel far from my marina and with twins could limp home on one engine, but certainly do not want to experience an impeller failure. Currently I have two years and 220 hours on my raw water impellers and trying to figure out when to replace them.
Thank you for your valuable insights.

Longest I have gone is about 500 hours on my single engine. Now I mostly replace somewhere between 200-500 hours based on just when I feel it is a good time.

 

[Lepke]

I've been on the water, on my own boat since 1961. Where possible in my careers I lived aboard. I check my impellers yearly, more often on commercial boats doing many hours.
Time and heat damages impellers. I don't close my seacocks except for maintenance. So I never start water pumps dry. When I change or inspect impellers, I grease the inside of the housing and cover plate. This gives impellers more suction on their initial startup and keeps them from getting hot while dry.
I have no idea of my impellers age. If they show any sign of cracking or hardening, I replace them. I can't remember any impeller failure.
Spare impellers are stored, sealed in a food saver bag, in a cool place. I have found stored impellers left in the air to deteriorate over time.

 

[twistedtree]

Re inspecting impellers vs just replacing them, how do you thoroughly inspect the impeller without removing it? It seems to me you would have to remove it to really see its condition. My feeling is that by then you have done all the hard work - draining the water, removing the cover, pulling the impeller, and removing the pump to do all the above if required - so why not replace with a new impeller and be done with it. It's the cost of the impeller, which I admit can be $100 or more for a big one, but only $25-$30 for a generator.


I guess I'm showing my dislike of the job of replacing impellers. Just draining the system is a PITA because I don't want to just dump salt water all over the place. And larger impellers can be a real bear to get installed. So my preference is to go in, get out, not have to go back until some prescribed time later, and have a reliable boat in the mean time.