Back in 1995 the FSM for Rams has a test for the clutch fan that involves using a heat gun aimed at the fan clutch and listening for the change in sound when it thermally locks up and raises the rpm of the fan to engine speed.
Back about 1998 when I tried this test I realized I had a 12 volt powered adjustable Stroboscope with a digital rpm readout from mining work that I had bought to field check the rpm of pump pulleys and electric motors. I got it out and found that i could easily measure the rpm of the fan, and the boost in rpm when the Magnum 5.9 V8 fan clutch locks.
The cost of these has come down since the 1980s:
https://www.amazon.com/Landtek-Instrumen...rds=StrobescopeMy fuzzy memory tells me the early 2000’s 4.7 V8 thermal clutch slips quite a bit more when unlocked because it has a lower viscosity silicone fluid as a EPA fuel economy improver. When Chrysler press release came out that year and touted that change I thought about buying one and attempting to use it on my 1995.