A. Yes, but only a little bit (check out this calculator if you want to see how much). A gallon of diesel at 16°F, for example, weighs 7.1 pounds; that same gallon at 106°F weighs 6.8 pounds. To put it another way, in the worst case scenario (largest tank, biggest temperature shift), the weight difference due to temperature change will never exceed 50 pounds or so.