I only have to drive my 6.0 five miles on 35 mph secondaries to get to work - Within the first half of a high 20 degree F trip, I'm getting heat without a radiator cover or plugging in my block. The first mile is flat, the next 1.5 miles are down hill, another .5 mile of flats, before a 1.5 mile climb and another .5 mile of flats. Work and home are on tall ridges and there is a valley in between them creating over 250' of descent and climb. Note I'm getting heat with the truck running downhill or flat for 2.5 miles before it has to really start working to climb out of the valley. Coolant temp is about 165 degrees and transmission oil is about 130 after those five miles. This is not my daily driver and I typically make trips that are longer with the engine running 180-190 degrees.