The XE 20d AWD is rated at 30 city/40 highway and 34 combined. The drive to and from Auburn is almost entirely highway, so I knew matching the highway rating would be easy enough. The XE has a 14.8 gallon tank, so I was looking at a minimum of 600 miles per tank and four fills for the trip, counting the initial pre-departure fill. I had two main concerns: first, this was a new route, so I didn't know how available diesel would be along I-75; second, crossing the Appalachian Mountains was going to severely cut into my overall average.
The first worry turned out to be a nonissue, especially as we went further south. Not once was I forced to go from station to station looking for a lone green-handled pump. People in the South love their Cummins, Powerstroke, and Duramax-powered trucks, meaning diesel pumps were plentiful. Rolling up in a Jaguar does garner attention, though. An older gentleman even asked if I knew that I was putting diesel in the car. It seems he didn't have much faith in my reading comprehension skills.
The mountains were more of a problem. There was literally no getting around them, but were west of the highest parts, so it could have been worse. The indicated fuel economy dropped by 4 mpg on the way up, from 47 mpg to 43. Still, I managed more than 650 miles from a tank, though I was starting to push my luck. We filled up for the short final leg. By the time we rolled into Auburn, the display indicated 44 mpg – pretty damn good, I'd say. It held there for the entire trip. Calculating the actual mileage revealed the computer was generous by 2 mpg, but that's par for the course. Few automakers display precise numbers.
The relative ease of getting this sort of fuel economy was complemented by the price of diesel. At each one of my four stops, diesel cost less than premium, the required fuel in all of the XE's gasoline engines. According to AAA, the same is true nationwide. It also helps that, on average, the South has the cheapest fuel in the nation.
There's a $1,500 premium for the diesel, meaning it takes about two and a half years of driving 12,000 miles a year to make up the difference and even less time if you drive more than that. Those calculations are based on the EPA combined ratings and AAA national average fuel costs. If you lean more highway or city, your mileage may vary. The infrequent fill-ups are worth consideration as well, though so are the dirty diesel pumps.
To get these numbers, I didn't have to adjust my driving one bit. I kept up with left-lane traffic the entire way. During her stints, my wife set the pace. There was no attempt to hypermile, no ginger use of the accelerator, and we had the HVAC set to 68 degrees. The diesel engine just kept chugging along, giving me power to pass when I needed it, settling down the rest of the time. It may be a bit cranky at idle, but once you get moving wind noise overcomes any diesel clatter.
If I had more time, then I would have slowed down, turned off the creature comforts, and been a bit more prepared in my route mapping. As it stands, this trip was a great baseline for future fuel economy comparisons. I was already a big fan of this car. Taking this thing on for a long weekend drive further cemented my opinion.