I use a digital infrared thermometer. You can find decent ones on Amazon for $25-35.00 Normal running temp for mine on a warm Summer day is around 110-115 degrees. What you're looking for is all of them pretty equal.
Vaughan & Tracy 2013 RW 36RL, 2013 F350 DRW CC, 2016 Focus. MorRyde IS, MorRyde pinbox, disc brakes, Comfort Ride Hitch. "Life is to be embraced, Grab it with both arms ! "