How many years on one impeller??

[KD4UPL]

I've got a '97 Mercruiser 5.7L with an Alpha 1. I put less than 50 hours a year on my boat; all in freshwater. The last time the impeller was changed was 6 years ago. The boat runs the same temp. it always has; about 160 degrees according to the gauge. Should I replace the impeller just because it's been so many years? Will the engine start to run a bit hotter when it's failing? When an impeller wears out does it just quit or give warning?
I know impellers are cheap but it's all the work in getting to it that I don't like.

 

[bspeth]

Re: How many years on one impeller??

Its very easy to do,I plan on doing mine every two years.I tink you should replace it.JMO.

 

[thumpar]

Re: How many years on one impeller??

We only put about 15 hours a year on the Alpha and I changed it every 2 years. It does not give a warning when it is about to go. It is really easy to do and you should be pulling the drive to check other stuff like gimbal bearing and u-joints.

 

[ziggy]

Re: How many years on one impeller??

on my mc-1. which if ya wanna call it, is a pre alpha. same impeller as alpha though. mc-1 thru alpha use the same impeller. imho these impellers are good for 2 years now. if ya don't abuse them once. i've been R&Ring mine yearly till last year. i stayed cool this year which was 2nd season on one impeller. i'm changing it this year and will post up a pic. all of my previous impellers had been abused at least once. all showed a curve to the blade. one had some melting due to low flow on the hose at my house.
the op has a genII. i've only seen a couple of them. but they sure look bigger and more robust. i'm near sure my buddy's been getting 4 or 5 years out of them. if not abused. the ones i've seen look pretty good even after that amount of time.
all that said.
the impeller is your first line of defense for not overheating. imho, it's not to be taken lightly. better safe than sorry. R&R it. imho.

genII and alpha impellers are totally different.

if ya wanna know what mercrusier has to say about it. go look at s/m #14 (genII drives). i'm sure it'd tell the proper interval for R&Ring the impeller. + the proper criteria for inspection. must say though. if yer lookng at it. might as well replace it. it's not that easy to go get.

 

[stonyloam]

Re: How many years on one impeller??

I do mine every 2 years. And for a 470 engine IMHO that should be the rule.

 

[achris]

Re: How many years on one impeller??

OP has a Gen II. Completely different impeller to the previous drives. The 'book' on them says 3 years or 300 hours.

At 6 years I would definitely be opening it up and having a look. And at only $42 for the impeller kit (impeller, all gaskets and a base plate), just replace it.

 

[generator12]

Re: How many years on one impeller??

I'm in no position to argue with any of you guys about this issue, but I'm curious as to why impeller degradation wouldn't be related to use. Most other rotating machinery components have service life rated in run-time, with possibly a time limit based on material decomposition. Exposure to corrosives or high temperatures or pressures would alter the equation, but it would still be based on run time.

Seems to me that impellers run in fresh water would be expected to outlast those run for similar hours in fresh water; and those run three or four times a summer would outlast those that operate every summer weekend.

Maybe someone could explain why there is a two-year replacement recommendation on these pump impellers regardless of use.

 

[thumpar]

Re: How many years on one impeller??

The impeller while in the housing is always flexed if used or not. I actually would expect those with more hours in clean water and not dry running to outlast those that are run less because they don't get a set to them.

If used in water impellers die when the cracks from the bend finally get too big and it destroys itself. I had it happen on my Bravo. For the price I would rather replace it every 2 years than be the one towed in.

 

[achris]

Re: How many years on one impeller??

I'm in no position to argue with any of you guys about this issue, but I'm curious as to why impeller degradation wouldn't be related to use. Most other rotating machinery components have service life rated in run-time, with possibly a time limit based on material decomposition. Exposure to corrosives or high temperatures or pressures would alter the equation, but it would still be based on run time.

Seems to me that impellers run in fresh water would be expected to outlast those run for similar hours in fresh water; and those run three or four times a summer would outlast those that operate every summer weekend.

Maybe someone could explain why there is a two-year replacement recommendation on these pump impellers regardless of use.

As Thumpar said, it's all about the 'set'. If the impeller sits unmoved, the blade get set a lot easier. The fact is, an engine used regularly will outlast one hardly used at all... When I had my boat shop, we had a fishing company as a client. Their engines got used for several hours every day... You know, those engines with a few thousand hours on were in better shape than the 15 year old 15HP evinrude that got taken out and used for about 2 hours on the christmas holidays....

Same goes for exhaust elbows. Use the boat regularly and the elbows actually last longer. My favourite saying... It's not using a boat that kills it, it's not using it....

Chris.....

 

[Scott Danforth]

Re: How many years on one impeller??

rubber starts to deteriorate due to age. as Chris mentioned, it also takes a set.

I use 2 years max on an impeller.

 

[ricohman]

Re: How many years on one impeller??

2 years eh? My new boat has 22 hours on it and next spring will be its third season. I may buy an impeller and swap it out during the season. Its so cold here rubber bits seem to last a very long time, but I sure don't want to cook a motor.

 

[achris]

Re: How many years on one impeller??

2 years eh? My new boat has 22 hours on it and next spring will be its third season. I may buy an impeller and swap it out during the season. Its so cold here rubber bits seem to last a very long time, but I sure don't want to cook a motor.

Good call.... Is a pretty easy equation... $42 impeller kit every 2 years, or save that and run the engine longer and risk thousands of dollars worth of damage.... Really, it's a no-brainer....

Chris....

 

[ricohman]

Re: How many years on one impeller??

Good call.... Is a pretty easy equation... $42 impeller kit every 2 years, or save that and run the engine longer and risk thousands of dollars worth of damage.... Really, it's a no-brainer....

Chris....

Yeah. I think next summer on a nice warm day this would be a good afternoon project. Since its -19 now all I can do is wish for next July.
I have a buddy that bought his boat new in 2003 and still runs the original impeller. Maybe I should invite him out and change his as well.

 

[Walt T]

Re: How many years on one impeller??

I know a guy who got 20 years out of his Merc impeller. Actually looked pretty good when I replaced it. Did the entire housing too. Doesn't mean you should leave yours in for 20 years, this is just one of those anecdotal things that I put up just for the heck of it. I replaced a customers battery once and the stamp on the side of it showed the battery was 10 years old. Customer said it was fine, always had been. I replaced it because I realized how old it was. Then there was the guy who never ever greased his trailer bearings. Gave me a blank stare when I asked him how often he did that. This is a guy who tows to Lake Powell from Denver several times a year, and goes water skiing locally pretty much every weekend. The bearings really weren't all that bad, just spotted a bit. Probably could have repacked them and let them go. Just odd how some folks equipment gives them nothing but trouble even though they follow all maintenance recommendations, and then some folks totally ignore those recommendations and have nary a problem.

 

[spdracr39]

Re: How many years on one impeller??

I know it's not a popular approach but I run off of a " If it ain't broke don't fix it" theory. I do not operate on big water or rarely at night when its lonely though so there are always options available to get back home. Creating a leak, misaligned something, or twisting off a bolt make it not worth the risk for me but that is just my way not saying it is the best way. I also am the only one that drives the boat and always watch the gauges.

 

[OldNBold51]

Re: How many years on one impeller??

I know it's not a popular approach but I run off of a " If it ain't broke don't fix it" theory..

I used to operate off that theory until the I suffered a $200 tow of shame because I let the impeller go too long. I also had to replace the exhaust flappers because i burned them up too.

I've changed my views on preventive maintenance. I think of my boat like a small single engine airplane. While I want to "take off", I do a pre-flight and am looking for reasons to stay on the ground. If I can't find anything wrong or near the end of it's service life, i take off.

 

[haulnazz15]

Re: How many years on one impeller??

I usually run 3-4 years on impellers for the MC-1 drive, running around 15-20 hours a year. I don't change lube more than every other year, either. Sure, it's against Mercruiser's recommendations, but the boat's been running fine for 35+ years so we don't change the regimen.

 

[FreeBeeTony]

Re: How many years on one impeller??

Good call.... Is a pretty easy equation... $42 impeller kit every 2 years, or save that and run the engine longer and risk thousands of dollars worth of damage.... Really, it's a no-brainer....

Chris....

I see where some of Don's sarcasm went..........lol

 

[phillyg]

Re: How many years on one impeller??

Six years is a long time; you're probably overdue. When they go there's generally no warning except your overtemp alert.

 

[achris]

Re: How many years on one impeller??

I know it's not a popular approach but I run off of a " If it ain't broke don't fix it" theory. I do not operate on big water or rarely at night when its lonely though so there are always options available to get back home. Creating a leak, misaligned something, or twisting off a bolt make it not worth the risk for me but that is just my way not saying it is the best way. I also am the only one that drives the boat and always watch the gauges.

By not doing the maintenance when it's due, you are almost guaranteeing that nuts and bolts will be seized and give you trouble. I think that's what is called a 'self-fulfilling prophesy'...

When I installed my engine new in 2006, I took each bolt out of the drive and put a liberal coat of grease on them, each and every one! Each time I do the service now, they all come out like they were put in yesterday....Same with my trailer brake caliper bolts. I put a good quality water-proof grease on them and 5 years later, when I needed to replace the pads, out they came, just like new....

Just saying...

Chris.........

BTW... Aren't we suppose to be helping people do the right thing here? Not telling them how great it is to avoid doing the maintenance? :facepalm: