Its a bunch of bull both pumps have the same housing, same passage sizes and 8 bladed impellers, , If you go back and look at summits web page for that item it says its a rebuilt unit I.E stock casting with there bearings and parts and I bet if you look down in at the impeller blades they dont have as much area as the old blades, thats what the end cap does it helps contain the water around the impeller, some also sale the so called heavy duty pump, witch are really for cars and trucks with a/c witch moves the water thru slower so it absorbs more heat, witch is bleed of by a larger radiator, if freezing weather isnt a problem then straight water with a anti rust and lube additive will run cooler than anti freeze, true severve duty has an extra nose bearing,