Impeller Change Interval

I put about 100 hours per season on my 820's. I change my impellers about every 3 years. And when I pull them they are like new. If I saw damage/wear I'd change them sooner. But for 20 seasons now, knock wood, I've never had an impeller issue. I have a dock box filled with used but perfectly fine impellers

Do you think any body opens the back plate and does an inspection? If everything looks good leave 'em in?

I have 820 Mans as well and I do them every 2 years. Once went 3 years and there were no issues and the impellers appeared fine.

Probably the cheapest item to maintain AND the most important.
For the mains-Low hours every two years. High hours every other oil change.
Gen-sets, every other oil change.

This schedule works perfect four our big trip every two years.
Yes, the main impellers are good but hard before we deploy.
Gen-set impellers are usually gone. We rotate 2 gen-sets.

Now outboards and stern drives, They pick up more silt and sand.
Every year for sure.

I have Detroit mains and a Onan and Perkins generators. I pull mine once or twice a year. When I install, I grease the inside housing and end plate. It's that way in old Detroit manuals. I change mine every 5 years. At least 500 hours on the mains, probably a lot more. Even then they look ok, no cracks or heat damage. I save some as emergency spares. Never had a failure. The wp grease doesn't last long, but I figure it helps on the first start.

I'm about the same on my little 6-71s.
But I'm on the Great Lakes and I'm a good year with 80 hours. So I think that has a lot to do with it. Biggest issue is mine are a PITA to get to
Viking did a great job packing 10# of s*"t into a 5# bag. There is zero room at that end.

I run Volvo D-6 mains and average 100 hours per year. Generally change out every 2 years. Once, I went 3 years and the impellers looked great when I replaced them. I'm more comfortable with every 2 years just to be on the safe side. I always keep the most recently removed units as spares in case I lose one.

On my Onan gen set which has Yanmar power, I change out every other year even though it receives very light use. I'm more concerned about a loss of flexibility in the vanes.

I changed mine on my MAN 1550's at 2yrs and 150hrs or so. They needed to changed. Some nicks in the a couple of the blades on each one.

Great post thank you all! At 100hrs per year , I'm in the two to three year on DD mains and two years on the smaller generator. And the Jabsco belt driven DD impellers always look fine.

I did my Spring sea trial to check the numbers and get the baselines. The mains with the new impellers were 2° cooler with similar water and air temps.

I do not know if it is feasible in large engines, but I have seen transparent caps of impellers, would be methacrylate or something similar.
and I found it very accurate.
with a quick glance you had a good idea of what was inside.

That's a great idea all the pump builders should do, makes great sense ! Here that Jabsco, Sherwood , Johnson ....etc. would save on a lot of unnecessary impeller changes....but they want to sell you over priced impellers, it's a big part of their business right?

There's more to impeller inspection than verifying the presence of vanes. Impellers can "set" to the point that the vanes bear no pressure on the bore and bypass the water instead of moving it along to the cam. One pair of 3406 Cats I worked on, had impellers that were 100% intact but weren't pumping sufficient water to cool the fiberglass exhaust, causing it to deform and leak. The vanes were permanently bent due to the direction of rotation. The vanes should be very nearly straight out axially, similar to new, to pump effectively, when inspected.

The see through is a good idea for day to dayquick inspections, but it doesn't tell you anything about the structural integrity. Could be skipping on its hub for all you know aside from the other problems mentioned. Change 'em every 2-3 years - heat is a diesels worst enemy

That's true , but knowing I changed the impellers recently ,it would still be nice to at lest have a visual on them with out disassembly . They should still be changed 500hr or so intervals , just my opinion .