Modern, computer laden cars make tracking mpg easy, and fun at times. My '09 Avalanche has the 5.3 LS engine, 6 speed auto, and what they call Active Fuel Management (cuts half the cylinders at certain cruise situations). About a year ago when it had just over 20k miles the readout for overall mileage hit 18, not bad for a 6000# brick. Then I put a couple thousand miles hauling a trailer full of Model A parts that equalled a car, about half of it mountains, and the overall dropped to 17. In the last 3-4k miles it's been creeping back up, but has only gotten back to 17.4, still not too bad for the utility derived. When cruising down the hiway, on the flat, at 75 or so, it'll drop down to 4 cylinder mode, and the instant fuel economy reading will jump up into the 30s Now.....my brides Mini, on the other hand, shows 38 mpg on the overall calculation at 20k miles.

The fun cars, different story. No comuputers, both 59ab, '39 three speeds, and 3.78 rears..................10 mpg about.