I know there've been lots of discussions regarding this. I always thought my 83 was getting about 28 MPG. If I run the tank down to say about 2 gallons left inside, I routinely calculate out to 32~33 MPG. I know it has to do with hauling a lot less fuel around. So if you get crappy mileage calculations, but routinely fill up say from about a 1/4 tank or so you actually may be getting calculations skewed by weight of the fuel. Since I now have found a reliable diesel station near work I can risk letting the tank run down pretty low. Still haven't let it run to light on conditions because I don't know if the damn thing works or not.
Happy Turkey Day All!!

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1985 300D 197K - Semi-Daily Driver Diesel
1998 Volvo V70 AWD 226K - Daily Driver 2
1998 Volvo S70 140K - Wife's DD
2003 GMC Sonoma ZR2 Option - Rusty Truck
THE BABY 1958 220S Sedan 66K All original, never restored and never will be.