The Pontiac engineers seemed to think a smaller water pump pulley made a difference. They have a smaller water pump pulley and larger crank pulley on AC cars than non AC cars. I'm assuming the AC cars work harder than the non AC cars and generate more heat, that added with the heat from the compressor and other AC equipment would require extra cooling. I could be wrong about that. Not only does the smaller WP pulley turn the water pump faster resulting in higher coolant flow it also rotates the fan faster resulting in more air flow as well. I would think that would aid cooling considerably, especially at a red light in hot weather with the AC running. A 1968 eight cylinder PS car has a 7-1/4" dia crank pulley and an 8" dia WP pulley. Every rotation of the crank results in only 0.91 rotation of the WP. The same car equiped with AC and PS has an 8" dia crank pulley and a 5-11/16" dia WP pulley, resulting in 1.41 revolutions of the water pump for every rotation of the crank. If my math is correct [a big IF] that's a 55% increase in water pump rotation over the PS only car. Replacing the 8" dia 9786819 WP pulley on a PS car with a 5-11/16" dia 9788886 WP pulley and leaving the crank pulley stock will result in the WP turning 1.27 times for every crank rotation, an increase of 39%. Again, IF my math is correct.
I wonder if AC equiped car water pumps wore out faster?
That being said, the Pontiac engineers did a pretty good job designing our engines including the cooling system. I've never had overheating problems from any of the stock Pontiacs I've owned. Including a Tropedo Back, Chieftain, Catalina Wagon, GTO and now the Firebird. If the cars are in good stock condition they should run fine the way they were designed to run. There are gobs of 60s Pontiacs out there running every day summer and winter with no cooling and/or heating problems. When we start to modify them it's a different story. They were designed to run the way they were manufactured not the way they get modified.
