In my opinion yankee and kmac are both right. One's leaning towards maximum usefull longevity and the other towards minimum inspection intervals. Sherwood or Jabsco, if it was mine, I'd pull the impeller every 250 hours or annually whichever came first and replace it. What are they, 70 or 80 dollars with port supply, and you don't have to chase down the broken off pieces. 500 hours is the longest I see them going without any loss of efficiency.
You are both doing way better than me. Last weekend I changed the one year old 17000K on my B series Sherwood 1730C and the blades were folded back holding the shape of the cam. Today I changed out a pair of Jabsco profile Q's with 700 hours on them on Detroit 12-71's and 4 of the 12 blades were gone, both sides.
I used to change mine every spring before splashing the boat, that was on a 41P volvo, put on aprox 500-700 hours a season. I always pulled the old impellor out and saved it for a spare after pickleing the engine for the winter.
If the cams are worn the impellers do not last as long. I always put in a new impeller and inspect the cam in the spring and usually get the season out of the impeller,around 1100 hrs. I have run impellers in a washdown pump for 5000 hrs ,but when they go they don't cause an overheat or plug up the heat exchanger.
eyschulman, get a seal kit for your 6068. There was some confusion as to what was actually installed in the pump in my engine. Local Deere dealer (major lack of marine dealer) ordered a kit for me, it had a mechanical seal in it. My pump only had a lip type seal. Moral of the story is to have a dealer that can accurately use your engine numbers to order the correct parts.
The impeller for a 660hp From Caterpillar is $ 300...I put 50 to 70 hrs a week on the motor....iam not looking to change it to often....I think most guys will know by a visual or sound that something is wrong
Did anyone ever notice this. If you hold new Jabsco and Sherwood impellers for the same pump side by side; the Jabsco impeller seems to me to be the superior product and from experience, the Jabsco lasts longer b/4 the vanes start to crack at their base. So although I have a Shewood pump, I always use a Jabsco impeller.