I like to crack a joke here and there. After I switched to a 180F thermostat and did a grille shutter delete in my RAM 1500, the fuel economy got slightly worse. Unless I run hard or tow a trailer, the oil won't get past about 190F~200F (if it's scorching outside). Driving around town, it will take forever to get to 185F. I switched from Mobil 1 FS 0W-40 to Mobil 1 EP 5W-20, and my fuel economy is awesome now, and that's on 87 octane gas. The owner's manual recommended 89 octane, but that is most likely due to the ridiculous temperatures of 220F+ that this engine was running at. Like many, I am also chasing the best fuel economy possible. Why was I running 0W-40 in there before? To compensate for the ridiculous coolant and oil temperatures while towing. Even a 2000 lbs trailer would bring the temperatures up to ~240F~245F. That's no longer the case.Fuel economy is calculated by distance traveled / fuel consumed. Driving a vehicle less will simply accumulate fewer miles on that vehicle, and does not necessarily change the vehicle's calculated fuel economy. In fact, letting the vehicle sit with fuel in the tank is likely to cause increased evaporative emissions and actually reduce the fuel economy. But I appreciate the attempt at humor.