Which water pump replacement?

All else being equal, which of these impellers will flow better? I know which one SHOULD last longer, but I've only ever seen the stamped steel style.

or

As an industrial designer with no formal fluid/pump/physics training, who as fate would have it has designed many an impeller (hand held blow dryers, and equipment cooling fans), I'll hazard an opinion. The bottom one looks like it has the advantage. That there are more impeller blades standing so upright and more open to the fluid intake yet still occupying less space in the housing (therefore allowing more area for fluid flow) ought to win. On the other hand, the blades are of such a crude, turbulence creating geometry, it hardly looks efficient. So I am guessing, the top one uses less power for a given unit of work, but the bottom one can do lots more work and will suck lots more power while doing it. The sheet-metal impeller is a cost reduction choice over the cast piece. Not only are they cheaper to make, there are no secondary operations needed to clean up flash, and the multi step forming used to make the shaft sleeve is cheaper faster better than cleaning up a bore through a bunch of cast iorn. The cast impeller might require balancing.. maybe not, but the sheetmetal one almost certainly will not. I could very well be that the sheetmetal one pumps more fluid than the system even needs! Which is not necessarily good. The loads on the sheetmetal impeller's bushing could very well be much greater than the cast piece, and if it some crappy aftermarket supplier, it might have lousy bushing material and seals. I had a cheapo sheetmetal impeller waterpump go away in my volvo 850. I removed the OEM piece, which has a cast impeller and was still good when i did the timing belt 5-6 years ago. The bushing failed in the aftermarket sheetmetal waterpump at about 70k this summer. I bought the 2x as expensive OEM part (which now has a sheetmetal impeller...) in the hopes that the bushing and seals are of better quality. Even simple little water pumps have many coupled dependencies that extend into the system.

Shaun wrote:

As an industrial designer with no formal fluid/pump/physics training, who as fate would have it has designed many an impeller (hand held blow dryers, and equipment cooling fans), I'll hazard an opinion. The bottom one looks like it has the advantage. That there are more impeller blades standing so upright and more open to the fluid intake yet still occupying less space in the housing (therefore allowing more area for fluid flow) ought to win. On the other hand, the blades are of such a crude, turbulence creating geometry, it hardly looks efficient. So I am guessing, the top one uses less power for a given unit of work, but the bottom one can do lots more work and will suck lots more power while doing it. The sheet-metal impeller is a cost reduction choice over the cast piece. Not only are they cheaper to make, there are no secondary operations needed to clean up flash, and the multi step forming used to make the shaft sleeve is cheaper faster better than cleaning up a bore through a bunch of cast iorn. The cast impeller might require balancing.. maybe not, but the sheetmetal one almost certainly will not. I could very well be that the sheetmetal one pumps more fluid than the system even needs! Which is not necessarily good. The loads on the sheetmetal impeller's bushing could very well be much greater than the cast piece, and if it some crappy aftermarket supplier, it might have lousy bushing material and seals. I had a cheapo sheetmetal impeller waterpump go away in my volvo 850. I removed the OEM piece, which has a cast impeller and was still good when i did the timing belt 5-6 years ago. The bushing failed in the aftermarket sheetmetal waterpump at about 70k this summer. I bought the 2x as expensive OEM part (which now has a sheetmetal impeller...) in the hopes that the bushing and seals are of better quality. Even simple little water pumps have many coupled dependencies that extend into the system.

Having said that, do a calculation for dynamic head and gpm requirements and pick the pump that has the most appropriate curve on the supplied performance graph. (Your figures should be in the middle of the curve and slightly below it)

Shaun wrote: As an industrial designer with no formal fluid/pump/physics training, who as fate would have it has designed many an impeller (hand held blow dryers, and equipment cooling fans), I'll hazard an opinion. The bottom one looks like it has the advantage. That there are more impeller blades standing so upright and more open to the fluid intake yet still occupying less space in the housing (therefore allowing more area for fluid flow) ought to win. On the other hand, the blades are of such a crude, turbulence creating geometry, it hardly looks efficient. So I am guessing, the top one uses less power for a given unit of work, but the bottom one can do lots more work and will suck lots more power while doing it. The sheet-metal impeller is a cost reduction choice over the cast piece. Not only are they cheaper to make, there are no secondary operations needed to clean up flash, and the multi step forming used to make the shaft sleeve is cheaper faster better than cleaning up a bore through a bunch of cast iorn. The cast impeller might require balancing.. maybe not, but the sheetmetal one almost certainly will not. I could very well be that the sheetmetal one pumps more fluid than the system even needs! Which is not necessarily good. The loads on the sheetmetal impeller's bushing could very well be much greater than the cast piece, and if it some crappy aftermarket supplier, it might have lousy bushing material and seals. I had a cheapo sheetmetal impeller waterpump go away in my volvo 850. I removed the OEM piece, which has a cast impeller and was still good when i did the timing belt 5-6 years ago. The bushing failed in the aftermarket sheetmetal waterpump at about 70k this summer. I bought the 2x as expensive OEM part (which now has a sheetmetal impeller...) in the hopes that the bushing and seals are of better quality. Even simple little water pumps have many coupled dependencies that extend into the system.

I agree, but for different reasons. The bottom one is more shiny.

Is the OEM impeller cast or stamped? I would follow the OEMs lead, since they had the info to do the maths on performance, not just cost.

bearmtnmartin wrote:

I agree. That's a hellova first post for any topic!

There are no performance curves for these pumps on RockAuto. My gut feeling as a Mechanical engineer is that the cast pump will possibly flow less due to the reduced vane count, but with far less turbulence. The pump I'm looking at goes on an early-model Civic which will soon need great(er) cooling capacity. I've noticed that the pumps on later model Hondas all use stamped impellers and don't seem to have a problem with cavitation, but DO have problems with the impellers rusting apart. Subarus have cast impellers, and I've barely ever seen a Subaru water pump with rust on it.

Does it really matter????

If either will keep it cool, get something and forget about it until it needs replacement.

Here's the thing. Both would work just fine for the stock 60hp engine. Hell, I have trouble getting it up to temp in the winter! When you stick a turbo onto the front of it, things change though.

cast due to full back plane stamped the water has a way to flow off the back side.