Some people prefer straight electric fans to a clutch fan. But a clutch fan uses ZERO hp. As the engine revs, the clutch disengages above 3000 rpm. There are different versions available, thermo or rpm, but in general they disengage and freewheel as rpms rise, unless the engine is piping hot.

One disadvantage to any mechanical fan is of course the noise. Some fans are noisier than others, depending on the blade angle, flexibility of the fins, and stagger of the blades. Factory GM units used stiff steel blades on their clutch fans, but each blade had a curved lip at the tip, and staggered blades, to eliminate almost all noise. The fixed blade designs, GM or aftermarket, are rather noisy.

It's splitting hairs, but the 0-5 hp a clutch fan may use at 4000 rpm, well consider that an electric fan puts a drain on your electrical system, which puts a load on the alternator, which then of course uses a few horsepower to turn.

A popular do-it-yourself mod that people used to do was rig up a switch, off the gas pedal or carb throttle lever, to cut power to the alternator at wide open throttle. But over the years, some tests in magazines have proven that while you may save a couple hp by allowing your alternator to freewheel for a few seconds, your also taking power away from an MSD unit and/or spark plugs, so they recommended not bypassing your alternator for those few extra hp you may save.

Great to hear you may have solved your problem. I use Water Wetter (two bottles) and straight water in my system.