Winter blend fuel will slightly reduce gas mileage but not by a whole lot.

My 260e had a problem with poor mileage and poor performance that I spent almost a year trying to diagnose. Finally, I noticed a gas smell under the hood and traced it to the EHC that was leaking slightly. Fear of an engine fire led to shell out the $$$ for a new EHC and it cured the poor mileage and hesitation problem.