Happy to note that I'm using Carl's PWM in my '69 Camaro 461 BBC. Its working exactly as advertised, I'm currently using a 195° sensor and a 180° thermostat. My radiator is a new Cold Case unit with two 1.250" tubes and I'm using a modified set of Ford Contour 12" fans on a custom designed and built aluminum shroud that's about 1" deep inside. When I'm out driving just after the temp gauge hits 195° the fans go on (I have a LED indicator on my dash).
I included a dozen BeCool rubber flaps in the shroud design to help overall airflow at highway speeds. Generally speaking, its working OK but I think I need more CFM because the car runs a bit warmer than I'd like. On a typical 85° summer day on the highway, I can't get it below 200° while driving at 65 mph. And the minute I'm driving on local streets the temp climbs to 210°-220°. The car now has Vintage Air so there's a almost full width Condenser in front of the radiator. I have the sneaky feeling that if I could turn the fans off with a switch of some kind while on the highway, the temp would stay the same or maybe even go down? One of my friends suggested adding a pusher fan in front of the condenser but that seems like overkill.
I used a corvette kit to put a foam seal around the entire 4-sided perimeter of the shroud/radiator so no engine air is pulled in. I also have a full core support cover to keep air flowing thru the grill and towards the condenser/radiator.
Because of the serpentine setup, its pretty tight as far as space between the shroud and the belts so my choices for 12" fans is somewhat limited. I would've liked to use a Lincoln Mk VIII setup but it was just too deep. Plenty of guys have said 200° isn't that bad for a modded BBC in this car but I'd really like to figure out how to knock down the cruising temp to 195° or slightly under so the fans don't run all the time once the car is warmed up. I thought about the coolant mix but doubt that adding more distilled water to the 50/50 premix would really make any difference. I haven't touched the timing since last year and before the car had the AC it had the 4-core copper radiator and a mechanical fan. It had a 160° thermostat and ran at 175°-185° on a hot day on the highway, maybe 190° around town and only if I was in dead stop traffic would it creep up to 210°-220° and that was after 10-15 minutes of barely moving.
So even though the car is drivable, I'm hoping I can improve something. Is the answer more CFM or maybe something else?-Mike