The Mariah Owners Club - Problem with non-OEM water pump impellers

Just a note.

I had to replace the impeller on my 95 7.4L. Since I was replacing the entire kit, I ordered an aftermarket (non-Mercruiser/Quicksilver) replacement to save a few bucks. Got it in and all buttoned up, put the hose/ears on the lower unit and after a running for a bit, I wasn't happy with the water flow out of the exhaust. The temp gauge got to 180 and I shut it down (I've never run above 170).

Anyways, Mercruiser manual includes instructions for checking flow so I ran a hose from the outflow side of the pump to a pail and the flow was minimal (can't remember what the specs were but I was lucky to get 1/2 gal in the 60 seconds I watched it.

Well, tore the pump down and found that brand new aftermarket impeller had cracks on the base of the leading side of seceral vanes (see attached pics).

The guy at the Marine Max parts counter looked at it and said that wasn't the first one he's seen fail like that. He recognized that the inside collar was brass (see attached pic), Mercruiser uses a white nylon. He said Sierra, the maker, does a decent job with most of their aftermarket parts but not with impellers. Side-by-side I could also tell that the vanes on the OEM impeller felt stiffer that those on the aftermarket impeller.

Got the OEM impeller in and buttoned up, put the ears on her, fired her up and she spewed water a few seconds of running.

Anyways, just thought I'd share my experience.