All of the hose connections on an L6 water pump are suction.
That 1 3/8" inlet is designed for some early-models or a heavy truck engine. They had a t-stat housing that also had a 1 3/8" side outlet to send water right back into the engine instead of through the radiator. The idea is to keep more water flowing through the engine if the radiator is huge and the outside temperature low. Then the motor doesn't see cold-hot spikes and it runs better. My 63 292 came with that setup, and I took it all off. Another example of that configuration is the smallblock Dodge. They all have a hose from the intake base to the top of the water pump, and it serves the exact same purpose.
What you need to do is ask yourself if there is any water that can circulate all the time from BELOW the t-stat back into the water pump. The 292 does not have an in-the-block bypass like the 250's and smaller engines. If you have a heater core that is full-flow, that is, there is no valve to shut it off, then you can safely cap that 1 3/8" stub. Or if your core is junk and you have a loop of hose (like I've got right now), then the same thing applies, you can cap that stub off.
What I would do if I were in your shoes is to take that pump back, and get a new aluminum one. GMB (I think) is one manufacturer. They are sold through Checker/Kragen/Shucks. The new housings have a 3/4" female pipe thread hole instead of the 1 3/8" stub. You just have to screw a pipe plug in there and you're done. Lifetime warranty, too.
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David
newbie #4153
