Is Your Water Pump Overdrive, Underdrive, or Neither?

On all brands of engine that I have worked on [ many ], I have found that spinning the WP faster [ smaller pulley ] improves cooling. When using a mech fan, you are also turning the fan faster to pull more air through the rad core.
A shroud is also moooooooost important for idle/low speed air flow. The closer the fan blade tips are to the shroud, the better it will be at pulling air. You also need to seal the shroud to the rad so that ALL the air is pulled through the core, & not through extraneous gaps.