Reply to "Aluminum Water Pump Issue"

The missing passage is the recirc passage, a passage that comes into play only when the motor is warming up. Most motors are designed to constantly recirc coolant, even when warmed up, but not so with the Cleveland, it shuts off the recirc of coolant when it warms up.

You don't have to toss that pump if you don't want to, here's your choices:

(1) drill out the missing passage full size & use the correct Robertshaw 351C thermostat, #333-180. I'm not able to measure things at the moment, I'm only relying on memory, I believe the passage is about 5/8" diameter. Don't drill it until a definite figure can be provided. There is an older thread about the passage in this pump, you may want to do a search and find it.

(2) drill out the passage with a 1/4" drill & use a Windsor thermostat. Now your motor will constantly recirc a small amount of coolant, just like a Windsor.

(3) leave the passage blocked entirely and use no thermostat. Not advised.
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Info for everyone, I was reading a 1972 Ford OHO publication recently and ran across a small article about the 351C water pumps I hadn't read in decades. It stated the stamped steel paddle blade style impeller actually flows more coolant than the Boss 302 curved vane impeller, but the paddle blade impeller begins to cavitate at 5000 rpm. Even when cavitating the paddle blade impeller continues to pump coolant, but the amount of horsepower required by the pump more than doubles when it starts cavitating. With the Boss 302 curved vane impeller installed in the 351C pump casting the pumping capacity was somewhat less, but cavitation didn't set in until 7000 rpm. With the OD of the curved vane impeller cut down (either 1/4" or 1/2", I forget) the pump could operate at over 9000 rpm without cavitation. Cutting down the impeller OD resulted in a decrease of pumping capacity however.

I admit this is contrary to what I've recommended in the past, but it seems to me if your motor is seldom going to see over 5000 rpm then a stamped steel impeller is likely your best choice. If you want a motor that's ready for whatever you're going to throw at it, or if you want every part of the motor to compliment a 7000 rpm red-line, then the curved vane Edelbrock pump will be a better choice.

Based on the SAE paper about the Ford GT cooling system, an automobile's cooling system should be capable of flowing about 100 gpm to allow the car to sustain speeds in the 200 MPH range. None of the usual pump choices flow this much coolant. If you want to drive full gonzo like that, contact Larry at Pantera Parts Connection about the stage 4 Stewart pump he sells for the 351C (its actually a modified Windsor pump), its rated up to 160 gpm.

Stewart Components Ford Pumps