Couple drive 1,621.1 miles on one tank HOUSTON, May 10 (UPI) -- A U.S. couple said they averagef 84.1 miles per gallon on a 1,621.1 mile trip from Houston to Virginia in a diesel-powered Volkswagen Passat. John and Helen Taylor said they used their fuel-saving techniques, which they teach to students at their schools, to make the nine-day trek on only one tank of diesel in the six-speed manual car, USA Today reported Thursday. The Passat has a government rating of 31 mpg in the city, 43 on the highway and 35 in combined city/highway driving. The Taylors said their fuel economy-saving tricks include staying about 5 mph below all posted speed limits and never falling below a minimum posted speed limit on the highway. They said they also tried their hardest to avoid idling and having to turn the ignition off and on again.