TOPIC: Unusual Water Pump Impeller Failure

I'm curious as to whether anyone else has had this issue with a Sierra Marine Impeller.
While servicing the lower unit off an inline-6 Merc, but before opening the water pump housing, I turned the driveshaft and fealt an unusual lump-lump-lump in the driveshaft.
I suspected I would fine an impeller with some of the blades broken off, but what I found was that the brass hub in the impeller that should be permanently bonded to the rubber impeller had come loose. The brass was rotating with the driveshaft as the rubber impeller remained stationary.
A GREAT way to destroy a Merc, and another good reason for checking the impeller every Spring before going boating.
Thom

Thom, I have only seen this in my McCulloch's, so yea it does happen

Yep, I've heard of it (Sierra) happening too. Guess there aint a lot ya can do about it. Must have been a production "fail".

I know a guy who works at a boat repair shop who ran into this same problem with Sierra impellers, spinning the hub on Mercruiser units Thom. They won't install anything but O.E. now!

I stay away from after market junk too.

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The bitterness of poor quality is remembered long after the sweetness of low price is forgotton.

back in the day mercury also had that problem. when you inspect them try to peel the rubber from thr hub. if it is lose AT ALL replace it.

And,...I have learned since my initial post that this has been as issue with OEM - like Dave stated - and just gives more good reasoning to changing the impeller every Spring.
It would really pi$$ me off if I - or a customer - cooked a Stack-6 due to this failure.
At the moment,...Life is good in the Great PNW. WHEW,...
Thom Doc Frankenmerc

WOW, I'm glad I read this thread. Other than quality could there be another reason for this happening like clearence being too tight on the ends of impeller?

Thom;
You aren't the first person to have this problem although I have never encountered it myself. A possible cause is the impeller sticking to the housing. I have bought motors that the previous owners thought were stuck & drop the lower unit off & the powerhead was fine. Take the water pump apart & have to pry the old impeller out.
Tim

FWIW, I have a tube of Dow Corning 111.."Valve Lube and Sealant". Its a non curing silicone lube. I coat the impeller blades with it..(its some real slippery stuff!) Damn, I've pulled some impellers and it still on the blades. Never had a problem. Heck, I even got around after years of abuse my 125 Force a new impeller. Looked like new after maybe 6 years! A little lube that sticks sure seems to help.

Thom, I think it happens when the waterpump is run dry and then the engine shut down. The neoprene melts and it will glue the impeller to the waterpump sleeve. Next time the engine is started the "nut" breaks free from the impeller.

I've seen 'em get so hot from dry-running that the pump housing melts, then a ton of molten plastic drips down the center into the pump and hardens. It'll form perfectly around the driveshaft, just like it had been poured that way at the factory.

Then, the next time the motor is started, the hardened plastic chews the heck out of the impeller. Once the plastic melts that badly, the housing is shot and the insert gets welded in there anyway.

In that case the impeller will usually show severe heat damage, even burnt rubber.

Long time ago I had a Sierra impeller fail in an Evinrude 40hp, fried the motor.

I contacted Sierra and they not only replaced the impeller, they paid parts & labor for me to rebuild the powerhead. That was back in the 80's, their warranty policies may have changed since then. They supposedly corrected their impeller mfg issues and I've used plenty of Sierra impeller since then with no failures.

Last thought, wonder if the ethanol-laced fuels have anything to do with delamination of the metal-to-rubber bond. We know how well ethanol dissolves rubber hoses and seals!

Cheers......ed