Water pump impeller failures

[cj88]

Just wondering why some people seem to constantly have water pump failures while others can go years/hundreds of hours and theirs still look like new?

[Lepke]

If you look in an old Detroit Diesel manual, and find instructions on replacing an impeller, use a finger full of waterproof grease and grease the inside of the housing, cover plate, shaft and key. The grease helps seal the vanes to the housing making for better suction of the first startup and stop the overheating of vanes from rubbing on the inside before water is drawn into the pump. If you look closely at damaged impellers, usually they show heat damage as hard areas and cracks.

Greasing the shaft and key makes pulling the impeller easier. I've been doing this since the 1950s when my dad, a chief engineer, taught me. I change my impellers every 5 years whether they need it or not. That could be 5 trips from Astoria to Alaska and other excursions. I inspect the impellers every year and regrease. That includes 2 Detroit Diesels, A Perkins 4108 and Cummings 3A1-7 on generators.

[svHyLyte]

I'm not sure whether it's correct or not but I have been told that the amount of sediment in the water one's motoring through most often will have an effect on the longevity of one's impeller. We don't take chances with the issue, however, and replace the impeller annually or at 100 hours, whichever comes first. And use a good coating of water-proof grease as noted above!

FWIW...

[Sailmonkey]

We do nothing special, our home waters are milky with sediment, but our engine impeller is about 2’ below the waterline.

Another thing that may help us is impeller speed. Our water pump is driven off of the injector pump cam drive. So at most it’s spinning at half of engine speed (1500 rpm in our case). But more often than not closer to 750-900 rpm.

[cyan]

Probably should add that non-petroleum grease is safest. (silicone or glycerine) Some impeller materials are attacked by petroleum grease and some aren’t. It’s hard to determine if you just bought a nitrile impeller when it’s in an unmarked ziplock bag on a shelf in a dusty little shop on an island, in my experience.

[JOHNMARDALL]

Impeller failure is usually caused by the impeller running dry, frequently after the engine has not been run for a while, although the constant flexing as the blades meet the cam plate will eventually cause fatigue at the blade roots. We recommend installing a new impeller at the start of each boating year, as cheap insurance against burning the exhaust system and other damage caused by reduced raw water flow.
As I don't like to use petroleum based grease on rubber parts, I pack the pump body with non-pumice gel hand cleaner after installing a new impeller, knowing that the hand cleaner is a good lubricant that will be washed away in the first few minutes of running the engine.


I hope this helps.


John Mardall
Vetus Maxwell Boat Equipment

[JD-Odyssey]

I replace the impeller on our engine about every two years. It usually looks in pretty good shape when it gets pulled but I'd rather err on the side of caution. However, after my NL genset ate two impellers in less than 5 years and I had to dismantle and dislodge the pieces out of the heat exchanger, I decided to change that impeller yearly. I also bought a Speedseal for it. The Speedseal has a Teflon bearing that aids to reduce any friction.
JD

[a64pilot]

My pump is under the water line, so even the first start it’s full of water, it never had a dry start, normally an impeller will last a long time, I have only had one fail.
Contrast that say to some Catamarans whose generator is well above waterline, it seems they have many impeller failures and often as well, it’s the dry starts in my opinion.

As far as a lubricant, don’t use petroleum products, however we all have at least dish soap available.
I don’t bother lube mine, but as I said, it’s below the waterline and is full of water when I open the seacock.

[Mike Banks]

It is because some people set their hoses so that there is always some water in the pump at all times--and have the inlet to the raw water system not TOO far below the heeled waterline so that when the engine starts it draws water into the filter BEFORE all of the stale smelly water in the pump and hoses has been expelled.

Now--I do not know how all systems work, but mine used the warm sea water from the heat exchanger to cool the exhaust. If you have a dry exhaust, you need to have your pump outlet from the heat exchanger above the height of the raw water inlet, and preferably using a siphon-breaker.

[s/v Jedi]

1. cover (=wear plate) and cam damage. this rips up the impeller so sand the cover smooth and polish up the cam so there are no burrs or sharp edges.

2. running dry: the hose from the sea strainer should attach to the pump from above... i.e. arrive at the pump higher than the pump inlet. This makes sure that when the motor is stopped, there is always some water standing there to lubricate during the next start.

For gensets I recommend to remove the impeller and use an electric submersible magnetic drive March pump (LC3) and connect that to the genset electric output

[cj88]

Thanks for all the useful insights and tips. I'll keep them in mind.

[RaymondR]

Originally Posted by cyan

Probably should add that non-petroleum grease is safest. (silicone or glycerine) Some impeller materials are attacked by petroleum grease and some aren’t. It’s hard to determine if you just bought a nitrile impeller when it’s in an unmarked ziplock bag on a shelf in a dusty little shop on an island, in my experience.

I use glycerine which I buy in the supermarket. (I don't know why they sell water pump lubricant in a supermarket but I have my suspicions)

[bwindrope]

Interesting thread. I've never had any trouble here in the PNW. Replace mine every few years on my Universal 5432 and they still look new. As others have said I've only ever heard of issues if you are motoring in rivers or other silty places. My intake for the seawater cooling system is about 12-18" below water line, so plenty deep to avoid the surface muck. I never even have to clean out my water strainer, though I check it often.

I've never used anything on my impeller when I replace them. Has never mattered. I have put about 1700 hours on my diesel and gone through a good handful of impellers, only replaced out of caution.

Curious what is causing trouble for others.