I thought this might interest you guys so I wrote it up!

I recently took a nearly 3,000 mile trip with the X5. At one point I encountered a very long 55mph construction zone where there was absolutely no traffic. I set the cruise control at 61mph. When I did this, I realized that my on-board fuel range calculator kept climbing. And climbing. And climbing. It kept climbing to a point when the distance on my trip meter (which I had reset at my previous fuel stop) and remaining fuel range equaled nearly 650 miles. I then started doing some mental math. If these calculations were correct and I divided them by what I approximated the fuel capacity to be (25 gallons) it yielded me a theoretical 26mpg. “Bullshit,” I thought to myself; “this thing is WAY OFF.” But then I noticed that the remaining fuel range and the trip meter were BOTH increasing at the same time. There came a point where the trip meter and remaining fuel range equaled nearly 665 miles. I then thought to myself, “ok, could this really be plausible? Could I get MORE than 650 miles out of a tank? Could I get 26mpg? Could I get MORE??? (Well, these calculations were a bit off because the tank is actually larger than 24 gallons, but not by much – and there are other variables explained below).

The following thought then entered my mind: “And what about the fact that I had not driven so conservatively since my last fill-up? Maybe, just maybe, could I get 700 miles out of the tank if I drove at a conservative, yet reasonable, speed??? And what about the fact that the fuel range goes to “- - - -“ before the fuel tank dries up? I damn well could get OVER 700 miles out of a tank!

I consulted the econometer to see at what speed the X5 returned the highest mpg. I started playing around with speeds on my cruise control and I found that the X5 3.0i’s “sweet spot” is at an indicated 64.5mph (62.5mph GPS-verified). At this speed, the econometer was at its highest (to the left of the unmarked hash mark). I don’t know what that hash means, but it appears to be 25mpg. The challenge was on. I was going to try to get over 700 miles out of a tank (i.e. over 26 mpg) under “reasonably conservative” driving habits.

Having decided I would test this out, I stopped for the night and planned on getting up really early to beat traffic so I could get as much of an uninterrupted run as possible. Before going to bed, I opened up my owner’s manual to get the precise BMW fuel specifications. I came to find out that my 24-gallon fuel tank capacity was wrong, but not too far off. The manual states that the fuel tank capacity is approximately 24.6 gallons and that the reserve is approximately 2.0 gallons (for the 3.0i – according to the manual, the V8 cars have a 2.5 gallon reserve tank). This equals a total of approximately 26.6 gallons of fuel. That means that if I could find a way to make the tank return the 700 miles I guessed it could earlier in the day, it would mean the car would return a theoretical 26.31mpg. An SUV RETURNING OVER 26MPG?!?!?! Maybe the car computer wasn’t full of shit earlier when I calculated a rough 26mpg (even based on an incorrect 24 gallon fuel tank capacity). Needless to say, I couldn’t believe my calculations. I was itchin’ to get going the next morning to see what would happen. I went to bed VERY motivated to realize my calculations.

For reference, here are the specs of the test mule:

Vehicle: 2003 X5 3.0i
Odometer: 138,000 Miles
Transmission: Automatic
Suspension: Completely Ruined Stock (needs all new bushings, ball joints, and shocks)
Oil Consumption: 1quart/3,000 miles (NOT A TYPO)
Miscellaneous: Aerodynamic inefficiencies such as protruding front left wheel well liner (adds drag and therefore decreases fuel economy)
Cargo: Approximately 100lbs of personal items in the trunk
Tire Pressures: 36psi Cold tire pressure (BMW recommends 39 so I was working the car harder; more friction, more drag, lower fuel consumption – stupid mistake)
Temperature: High ambient temperature reached into the high 90s
Route: Midwest Mountains (constant acceleration/deceleration up/down hills hurts fuel economy)
EPA Official Fuel Economy: 19mpg (highway) (that’s a theoretical 505.4 mile range at the maximum 26.6 fuel tank capacity BMW lists).

I rose at 4am the next morning to brim the tank until it was vomiting fuel and then sorted my tire pressures. My strategy was simple. Slowly accelerate up to speed, take as few pee-brakes as possible, and keep her at the 62.5mph “sweet spot.” (During my econometer testing the day before, I actually noticed that 52.2mph gave a slightly higher fuel economy than 62.5mph, but that’s not a practical speed to maintain on a highway. After all, I want this write-up to be as realistic as possible. 62.5mph is much more reasonable (and realistic), even in 70mph zones. Trust me, it’s actually not bad going 62.5mph in a 70mph zone – I thought I was going to tear my hair out but I was totally fine). With that, I set off.

During this test, I only came off cruise control 3 or 4 times and took 3 breaks. Of course, in the interest of staying realistic, I ran the air conditioning, radio, and charged my phone and GPS all at the same time for the duration of the test. Here are my findings with pictures for proof.

Picture 01: Computer readings shortly after topping up

Picture 02: Climbing

Picture 03: Climbing to a theoretical 666 mile range

Picture 04: Still at a theoretical 666 mile range

Picture 05: Theoretical 686 mile range (COULD THIS BE POSSIBLE?!?!?!)

Picture 06: Theoretical 686 mile range (This is starting to seem possible!!!)

Picture 07: Back down to a theoretical 668-mile range (damnit!)

Picture 08: Back up to a theoretical 680-mile range!

Picture 09: Up to a theoretical 685-mile range!!!

Picture 10: Down to a 671-mile range (the torture!)

Picture 11: Up to 680!

Picture 12: Down to 675

Picture 13: Down to just over 660

Picture 14: Hash marks after traveling 662.7 miles!

Picture 15: Finally, I ran out of balls after coming so close to my goal of 700 miles

Picture 16: I brimmed the tank until it was vomiting fuel again to see how much fuel I had consumed

That’s it – a total of 683.1 miles on a single tank of fuel in an utterly ruined 2003 X5 with tire pressures a bit below spec, A/C on, radio on, and the GPS and Phone drawing power. With a total fuel consumption of 25.59 gallons, that’s an unbelievable 26.69mpg. Having approximately 1.01 gallons left in the tank, I could have theoretically travelled another 26.69 miles for a theoretical fuel tank range of 709.8 miles!

Caveat: to be completely conservative and remove doubt, I’ll adjust the total mileage covered. Because the indicated speed was off by 2mph, it is plausible that the trip computer is off by the same margin (since both readings come from the wheel speed sensors). This means that I may have travelled a slightly shorter distance than the trip computer says (yeah, I didn’t think about verifying the distance via my GPS unit – my mistake). Being that this drive took about 12 hours, I’ll say that there may be a 24-mile distance discrepancy (2mph x 12 hours). Even at such a discrepancy (659.1 miles), the X5 still returned 25.76 miles per gallon.

Once more, think about the mule I used as the test subject and imagine what a perfectly operational X5 could do. I’d be willing to put my money on a solid 27-28mpg even after the adjustments for the wheel speed sensor discrepancy (kicking and screaming, but I honestly think it’s possible). At the consumption volume of this test (25.59 gallons), that’s a potential 716.52 miles – well over the 700-mile range I theorized the X5 could potentially achieve. And that’s adjusted for the speed/distance discrepancy built into the wheel speed sensors!

What a car. What a brilliant motor the M54 is.

I’m a believer.

Note: The server is not allowing me to host any pictures at the moment. Could a moderator please let me know if there's a problem with the server or if it's an intermittent glitch? Thanks!