Have you determined for sure the engine is overheating? Relying on an unreliable Chinese temp gauge as your source for determining this may be leading you down the wrong path. IF your temp gun is accurate and you are seeing around 200 degrees as you indicated after highway driving, I would consider that normal. If the temperature is actually 240 degreres as your gauge says, when you pull over and pick the RPM's up to 1500-2000, the fan should sound like wind tunnel and be completely locked-up to lower the temperature. You didn't say if there was overheating before you changed the coolant pump or if there was any change after changing it. Assuming you have the original timing cover with the two dividing plates, they need to be installed carefully and possibly modified a little to divert the water properly. There is a thread about this. I guess my final point would be to determine for sure accurately, if you have a problem before trying to fix it. That may mean buying and installing a quality gauge like an Autometer/Stewart Warner or similar, or making sure you have an accurate infra-red gun. 200-210 max real temperature would not concern me. I have owned many Pontiacs of that vintage including a 66 421 HO 9 passenger wagon with AC, 8 people on board, hauling a 19 ft. 3500 LB. boat all over the country without ever overheating. Stock cooling system. Good luck.
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