[sawdust123]

I have put about 13,000 miles on my '03 GT in the last six months. I generally get between 18 and 21 mpg and I have gotten as high as 24+.

Part of the reason the PT gets such poor mileage is aerodynamics. Wind resistance is a function of shape and frontal area. The PT's shape isn't very streamlined and the frontal area is huge. Speed is a big killer too. Drag is a cubic function w.r.t. speed if I recall correctly. This means if you double your speed, the drag increases by a factor of eight. My best mileage was at cruise control at about 65-70mph. A similar trip with cruise set just below 80 resulted in significantly lower mileage. Other mileage factors include tire inflation, use of A/C, terrain and of course driving style.

I would like to chime in about Crazy Eddie's mileage calculation. I believe his approach is removing precision, not adding it. Using a similar pump for fill up is about the best you can do. I tend to fill till the second click because many pumps shut off prematurely. I fill at maximum flow rate till the first click and at minimum flow rate till the second click. The slower fill rate reduces the chance that agitation inside the filling tube caused the pump to shut off prematurely.

I believe my approach gets me to within 0.25 gallons of filling up to the same point each time. If I got 240 miles per tank and put in 12 gallons, that would be 20 mpg. If sometimes I put in 11.75 or 12.25 gallons, I would have calculated 20.4 or 19.6 miles per gallon respectively. That is an error of a whopping +/-2% (100*0.4/20). That is pretty darned accurate in my book.

If you want to get anal about this, there are devices that plug into the fuel line and measure actual fuel consumption. Several of my old cars had this.