There are many routes to outstanding fuel efficiency, but it’s often diesel that’s chosen to demonstrate the highest mpg numbers and longest distances.

Mileage experts Helen and John Taylor achieved both, to become the world record holders for the longest distance driven on one tank of fuel, using a Volkswagen Passat TDI.

In driving from Houston, Texas to Sterling, Virginia, the Taylors drove 1,626 miles on a single 19.322 gallon fill of clean diesel. That equates to an average economy figure of 84.1 miles per gallon.

The Taylors were determined to make it a proper test too, rather than making it too easy. To that end, all the driving was done during the day in normal traffic conditions, rather than at night. The car was completely standard–a 140hp, 2.0-liter TDI, with a six-speed manual transmission–with 120 pounds of luggage in the trunk. The Taylors took turns at driving, and drove no more than 14 hours per day.

To ensure the test was conducted accurately, the speedometer was correctly calibrated for accuracy, recording parity at 20, 50 and 70 mph. The odometer was reading slightly under, so all figures were corrected to maintain accuracy.

The fuel used was verified by Senior Police Officer Daniel M. Rodriguez in Texas, then sealed and signed. Motel managers along the route also signed to confirm the seal was still intact, before it was finally signed for and removed by Deputy Sheriff Alonzo Perry at the end of the drive.

The Passat’s 84 mpg rating by the end of the drive is nearly double that rated by the EPA, with an official highway figure of 43 mpg. Many Volkswagen diesel drivers have found that the EPA figures for their cars are slightly pessimistic, and average economy figures of more than 40 mpg aren’t uncommon.

The Taylors’ endeavor has earned them a place in the record books, but we wouldn’t put it past the next record being in a Passat TDI too. The previous record-holder, at 1,526.6 miles, was also a Passat–the 1.6 TDI BlueMotion model, sold in Europe.

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This story originally appeared at Green Car Reports.