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Can you guys help me out - I have a problem. Have a 1991 GMC K2500, 3/4 ton, 5.7. Put a new GM crate motor in and it overheats. Does the water pump have to be a reverse pump because of the serpentine belt set up? It overheats under a load, but does fine sitting in the garage idling. Has a new thermostat and new radiator. Any ideas?
 

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Make sure you have a water by-pass between water pump and intake manifold. The new crate motors do not have a by-pass drilled into the block. I had the same problems of sudden overheating until I installed the by-pass. Hope this helps...Good luck.
 

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Yes - the serpentine belt setup requires a reverse-rotation water pump; if you use a conventional-rotation V-belt water pump with the serpentine setup, you will definitely have an overheating problem. The pumps are identical except for the impeller.

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JohnZ
CRG
'69 Z28 Fathom Green
 

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An easy way to check if the pump's running backwards is to start it cold and see which radiator hose gets hot first. If the lower hose heats up first the pump's going the wrong way.

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'69 RS Camaro
355 5-speed 4.11
 

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A standard rotation water pump will actually push water the right way if connected to a full serpentine system which DOES require a reverse flow. It will be dramitically reduced if so. If the water pump pulley is turning the same direction as the crank (clockwise from the front view) it is a standard rotation. If the crank and the water pump pulley are opposed rotation then the reverse rotation pump is required.

John is correct, the reverse pump is an impeller issue by design.

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STEVE JACK
ConceptOne Pulleys and Brackets
Northern/Southern Rodder Magazine's "Jack'Stands" author and creator
Techical forum/links at www.inccn.net/techforum.htm
 
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