In central Illinois it's usually pretty clear when stations begin dispensing number 1 diesel (and you notice it during fall, right before the cold really starts setting in). Winter blend diesel's additive package kills some of the energy content in the fuel, typically leading to a 2-3 mpg drop. After recently checking our '05 Jeep Liberty CRD's mileage, we fall right into the 2-3 mpg drop category. In fact, our current 24.3 mpg average is a 2.4 mpg drop over what we were seeing during the summer months (26.7 mpg).