I filled up after my first half tank of fuel. My Jetta Wagon TDI only got 37 mpg. Very disappointing. I then checked the tires because one of them looked low. All of them were low… about 10-15 psi each. So now I have gone through nearly an entire tank. I went 555 miles on 13.6 gallons of diesel. So I was close to 41 mpg. That is an acceptable number.