Wasted Impeller - Root Cause??

[ttmott]

Doing the routine maintenance and pulled this impeller from the starboard engine (Cat 3116 Sherwood Pump). Amazingly it cooled the engine. The impellers have about 140 hours on them and were last serviced June 2013. Other than maybe a worn cam (I don't know how to tell) what could possibly cause such carnage? The Port impeller had part of a vane missing but that is it.
Thanks
Tom
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[URL=http://s1012.photobucket.com/user/bumpythecat/media/SeaRay%20400DA/WastedStarbImpellerB_zpsf460c4c6.jpg.html][/URL]

 

[sdleo26]

That's crazy..., I just opened mine up after about the same hours over 2 plus years and they looked brand new... Those pics look like they were run through a grinder.... Did you get all the debris out ??

 

[ttmott]

Going into the heat exchanger this weekend.

 

[carterchapman]

Mine looked the same way after 3 years. PO did them every two - now so will I! My 8.1s on the last boat went 3 years no problem. Like yours, my CATS ran normal temps with all those vanes missing.

 

[fwebster]

Tom,

The vanes all get caught in the end cap on the heat exchanger nearest the water pump outlet. Several large bolts and the cap slips off, turn it over and count the vanes as you pick them out of the cap and end chamber on the heat exchanger. No need to disassemble anything else.

We have experienced early failures on several boat with Sherwood pumps using Sherwood replacement impeller kits. When we called Sherwood, we didn't really get a very solid answer except they think the impeller "copper bonds" to the pump housing and are ripped off when you crank the engine. Apparently, this is a problem more with winterized engines and those that have been sitting idle long enough for the sea water to evaporate from the pump housing. I've only experienced it when we were out of the water for an extended period of time during the winter when there was a mix up on some other parts we had ordered. I am usually on the hill 2-3 days in February, but we were out for almost 3 weeks waiting on replacement parts.

Not much of an answer, but it is the only thing we could learn when it happened here…………….

 

[ttmott]

Thanks Frank - I've had the HX caps off before, the only caution is this end also is used to pull the tubes so a couple of bolts need to go back in while the cap is off so you don't dump the coolant; ask me how I know this...... This boat gets used frequently and all through the winter months. The only time dried out was during the two month hall earlier this year.
These impellers are Johnson/Sherwood that I got from Depco. Depco moves a lot so stock so I doubt expired shelf life is a possibility. I noticed the cam leading edge has a significant step; a "bullnose" about 1/8" high. Wondering what that step is in other like pumps.

 

[ttmott]

The situation was concerning me so much that I had my mechanic stop by and look over the pump. The first thing found was the strainer basket was not tight to the housing (it had about a 1/4" rattle space) and we found a lot of debris in the bottom of the strainer housing; he thinks the pump was pulling debris through and it took out one or more of the vanes and that proceeded to destroy the other vanes; kind of a self eating watermelon..... I flared out the strainer basket lip so it seals well to the housing and cleaned out the HX and line from the strainer to the inlet of the pump.
Message-check out your strainers and make sure they can't pass the stuff they are suppose to filter.
Tom