CigDaze

I use the standard Merc plastic one. I've never had one fail, but I've heard that they can in some rare instances.

The advantage to the brass ones would be simply their superior hardness. They'd be less prone to scratches and thus a smoother surface would probably allow the impeller to live linger since it wont be riding on a rough and scored face. Of course in the event that something does happen to it, it's going to cost you a bunch more to replace.

Budman II

iTrader: (1)

The circulation pump on the front of the engine is really just along for the ride on most boats. I had a standard automotive type pump on mine for about ten years. Eventually, the vanes completely rusted out and it was not really even flowing anything, but the seawater pump produced so much pressure on its own that I did not even get a temperature fluctuation. In fact, I would not have even known it was bad if it had not started making a scraping sound from a piece of the impeller hitting the housing. In fact, a lot of the boats with high performance setups have replaced the circ pump with a simple crossover pipe to route the water directly into the engine - saves a few HP. I have often wondered if I could accomplish the same thing by simply removing the vanes from my circ pump.

I have been running one of the blue Globe impellers in my seawater pump with the plastic housing for several years. IMO, these things are great. I pull it out every year to inspect it, and the vanes still look great. Globe claims you can run these dry with no harm, but I still avoid doing that just in case. Unfortunately, they started having some issues with the hub tearing away from the impellers on some of their newer ones - probably a sourcing issue (read: switching to a far east supplier), so they are now being recalled and you cannot get them. Hopefully they will get the issue resolved, because I absolutely swear by mine.

88Fount33

The issue with the hard housing is that once it gets scratched up or gets wear grooves in it from the debris in the water, it is nearly impossible to get it to prime properly. The raw water pump is a positive displacement type pump as compared to the circulator pump that is a centrifugal type. When you use the "Kits" of housing and and impeller, you get new smooth surfaces on both and it makes it easier to seal. It must be sealed to be able to be self priming as it is normally located above the waterline of the boat and if the seal is compromised by scratches or grooves in the housing the new impeller vane will not deform into them and then they don't expel the trapped air. If you boat in crystal clear water without sand or other debris, then a metal housing would last a long time.

Keep this in mind. Sand is Silica Glass, and that is some pretty hard stuff, it is much harder than most metals, even hardened ones, therefore if a grain of sand is trapped into the rubber of one of the impeller lobes, it just goes around and around grinding into the metal housing. Abrasive compounds containing silica are used to lap valves in and to hone cylinder bores, Two years where I boat and I would guarantee you that even if the housing was made from Ceramic Silicon Carbide, it would be grooved up from the grit in the sea water, specially how shallow it is, constantly getting into low water areas to get to good anchorages.

offshoredrillin

great answer, i change mine yearly, new pump and plastic housing, i was just curious of the pros and cons and that answer makes all the sense.