Automotive water pumps

[Stephen Tashiro]

Having been forced to purchase a new water pump for my '89 Corolla, I am reminded of how unnaturally hard it is to turn the shaft on a new water pump - at least on the pumps for my old cars. Are all automotive water pumps like this?

Perhaps it's not a fair comparison, but when I think of equipment like kitchen blenders, it seems that there should be a way to design a watertight shaft that didn't have so much friction.

[Dan Hintz]

I doubt it's the watertight shaft that's causing the tightness (though I could be wrong, I don't know how they are designed). More than likely it's the method with which it moves water that causes it...

That said, blenders don't have to handle the pressure of a closed system, they only need to hold back the pressure behind 8-10" of liquid standing on top of the shaft.

[jason thigpen]

i've been an auto technician for many years. i can tell you that all new water pumps are pretty stiff right out of the box. you should be able to turn them by hand however. keep in mind that the shaft is 100% water tight. the shaft bearing also must tolerate the high lateral forces from the drive belt. there is literally zero play in the shaft bearing. if i took one out of the box and it was really easy to spin by hand, i wouldn't install it. i doubt it would last 10,000 miles.

[Stephen Tashiro]

if i took one out of the box and it was really easy to spin by hand, i wouldn't install it. i doubt it would last 10,000 miles.

I believe that. On the 2 leaky pumps I have removed the shafts turned freely. The most recent pump that went bad didn't leak but the shaft completely froze. It looks like part of the bearing assembly began to push out the end.

[Tom Hintz]

The drag is primarily at the seal. Remember that the water pump is exposed to the same water pressures as the rest of the cooling system so the shaft seals have to be robust or it will leak in a big way. the seals do break in a bit and the shaft spins easier once that happens but the difference is relatively small.
For a while we were using a specially built water pump on our race car motors because they spun so freely whichmeantt less horsepower loss. Unfortunately those pumps also tended to leak after very little running time. We quickly went back to the more traditional pumps and the seals that lasted longer.