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Old 12 May 2004, 08:01   #1
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Water Pump Impeller - change how often?

Hoping someone might be able to give some guidance on a sensible replacement policy for a water pump impeller - in my case for a Suzuki DF90.

I do the rest of the routine servicing myself, oils, filters, plugs, etc - no other problems as such to worry about so far - and I've always had a slight conscience about not doing this job. (Or more likely paying someone else to -unless anyone out there can convince me it's an easy job - I've changed car engines and gearboxes in the past but's that with the 'help' of e.g. a Haynes manual.).

On the other hand, I've been a member of a couple of dive clubs, and I'm not aware that the 3 RIB engines involved have had this job done at all in the last 5 years.

Occasional sandy beach use, but otherwise nothing too much which should be giving my impeller a particularly hard time. And 50 hrs per year absolute tops.
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Old 12 May 2004, 08:50   #2
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Hi Neil!
I've asked this question on a few different occasions and the response varies depending on who I spoke to.

There seems to be no hard and fast rule. Some replace the impeller every year after winter as a preventative measure. It's done after winter because this is when the impeller is more likely to deteriorate or will deteriorate most due to lack of use, becoming cold and brittle etc.

Others replace when necessary(when they can see the tell-tale weakening) which, if other potential causes for a weak tell-tale are eliminated e.g. blockage in passage leading to tell-tale, water intake blockage, thermostat problem etc.

I've got 2 books which refer to changing the impeller. RYA Book of Outboard Motors and Outboard Troubleshooter. The advice from shown is:

1)"So long as the engine is not started without cooling water, a water pump impeller should last many seasons. Nevertheless, some owners like to replace theirs as a preventative measure every season., while others wait for a reduced flow from the tell-tale as a sign that the impeller is starting to become worn."

One of the books does not advise as to when to change.

Hope that helps.
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Old 12 May 2004, 09:27   #3
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I asked a (Canadian) Mariner dealer about this recently and he said the following:

Check it once a year. If there is any noticable freying then replace it. Also, if you take it out of the casing and the impellor blades don't straighten within about 5 minutes then replace.

He seemed to use this as his own rule of thumb.

My local parts supplier is painfully expensive, but in the US or Canada things are a bit more reasonable. If I could source them cheap enough, I'd replace them yearly. Otherwise, a rule of thumb like the one above can be useful.
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Old 12 May 2004, 09:31   #4
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I told the dealer who serviced our engine that I was happy to replace it as a matter of course, but he inspected it and insisted that it was perfectly serviceable. I think that puts it on its third season now.
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Old 12 May 2004, 09:44   #5
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Water Pump Impellor

We change ours at the start of every season. As previously said they do become brittle over winter. It's about a 15 Minute job, and at a cost of around £15.00 for the impellor.Rather that than lose cooling 5 Miles out!
Trust this helps

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Old 12 May 2004, 10:04   #6
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Suzuki 50 (1982) - was running on its 2nd water pump impeller when I sold it last year.
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Old 12 May 2004, 12:29   #7
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Impellor changing

Hi Neil
I change impellers every year as a matter of course when i service a customers engine, would you leave your cam belt on your car cos it looks OK.???
I have had to strip quite a few engines to get the blades out of the water tubes and water galleries under the powerhead.
I have seen so many people run there engines before they lower into the water and lift the engine out while still running, i have read somewhere that an impeller will be damaged with as little as 15 seconds of running out of the water.
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Old 13 May 2004, 03:49   #8
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Neil

Always was my opinion to change the impeller every season as a matter of precaution. Most manufactures have now seem to have lengthened this to 300 hrs or every three years. Maintenance schedule should be in the owner’s handbook but I have a feeling Suzuki still recommend once a season.
The most important impeller change in the engines life is the first one; the engine manufactures never grease any of the studs or the drive shaft spines so hence important to do this on a newish engine. Quicksilver 101 is the best stuff I have found.
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Old 13 May 2004, 04:04   #9
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Thanks to all for the helpful advice.

On balance it sounds like this is worth doing - I think my plan is going to be to get a mobile engineer to come out and do it, so I can watch and pick of clues for doing the work myself in the future.
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Old 13 May 2004, 06:35   #10
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I have read somewhere that an impeller will be damaged with as little as 15 seconds of running out of the water.

When I did my PB2 I was told by the instructor that the night before any trip I should start up the outboard to make sure all was well, then again before leaving in the morning, then again before launching before finally trying her after launching. All apart from the last "dry"
Needless to say I didn't ever follow his advice and on the course his outboard seized
You get some strange ideas from folk , while I don't believe a short try of the engine is going to completely destroy an impeller in seconds, doing it again and again or running it for a any length of time will and it is not something you really want to be doing if you can avoid it.
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