New water pump 6 impellers whats up with that!

Wow. At .300+ net clearance, that is more of a stirring device than a pump.

With all of the intake uncovered on the back side, it should fit closer to the backplane than that. If this was an oldsmobile we would be welding a cover on the back of that impeller.

On a 385 block ford I would be looking for .050 to .100 total net clearance with the gasket. That would be split evenly between the front & rear of the impeller.

This is one of those times I just scratch my head and wonder if it has always looked like that. The last 318 I owned I bought new in 1973, and I never had the water pump off of it (great engine, lousy body). I am not going to tear the 318 in my Barracuda apart to measure it, but I do wonder if it has that much clearance. I think I will measure the differential pressure when I get a chance.

As for pump designs, you really should not be able to look in to the inlet bowl from the back of the impeller like that, unless the cover fits very close to the back of the impeller. Take a look at a later mopar pump, like the ones that run in reverse on a serpentine belt. Or look at the pump for a 4.0 Jeep. Or several other examples. Solid back impellers have replaced the folded impeller in many makes & models too.

The stack up of tolerances as various manufacturers make parts from different tools, reverse engineer stuff etc. can be vexing. This may be the case here, or perhaps it has always been this way. It would not be the first time I saw something mopar and asked myself how they got away with that.

If anybody has a 20+ year old pump and /or front cover they can measure that would be great. Since we know the net clearance on this new pump, how does it compare to the old one? And how well did the old one cool?

I asked in another thread for any available pulley measurements on A/C vs non-A/C cars. If you have a factory A/C car I would like to know the drive ratio for the water pump / fan assembly.

B.