[dataway]

I recently put a stock water pump in my new build with a clearanced plate, about .030". Looking down into the filler neck of the radiator (on test stand), I can't imagine much more water being forced through the radiator.

Not many people check their pump this way ... but if the water is a few inches below the top of the radiator you can take the cap off and see the flow through the tubes, it should be energetic. I would say a healthy pump will not dribble out, it won't water fall out, it will shoot out of each tube ... not like a nozzle on a garden hose, but more like an opened ended garden hose. It's a hard thing to quantify ... but you want to look in there and be able to say "yeah, I can imagine that is more than enough water to cool my engine"

Also people rarely mention actually feeling the radiator tanks. When the engine is running ... check the temp difference between the hot side tank and cool side ... you should easily be able to feel the difference with the engine running.

If both side are hot, there is probably a problem. Assuming you have enough water flow, then the problem not enough air flow.

If the hot side is hot, and the cool side is quite a bit cooler and the engine still over heats ... probably means enough air flow, but not enough water flow.

This assumes radiator and thermostat are in good working order.

If a person wanted to get scientific they could measure the temperature drop between the tanks with a infrared thermometer. I'm guessing somewhere in the Pontiac factory literature there is a specification for expected temp drop across the radiator at a give rpm/temp range.