I've only been driving my 03 (new to me) Expy for a few months now. Was getting around 16.5 mpg average. Now with the weather turning hot, and the AC on, looks like I'm getting around 14 + average. Wondering if that is similar to other's experiences?

Thanks for your input.

 

Being in NJ, you recently got screwed into having to use ethanol instead of MTBE as the primary oxygenate in your summer blend fuel.

Alcohol has a lower energy content and its blends get lower fuel economy numbers.

AC use will account for 1-2 mpg of fuel economy. Your figures are about right.

If you really want to save fuel, drive 50 mph and stay out of the left lane...

Steve

 

Mythbusters did an episode on this, episode #49. The results surprised me as I also thought that the A/C would take from the fuel economy. But... they drove two exactly identical trucks, f150's if I remember right, around an oval track filled with the exact same fuel, one with all windows down and the other with the A/C going and they found them to get the same MPG. They did another episode where they tested the myth that driving with the tailgate down will help get you more MPG. They drove 2 trucks the same route at the same speed one with it up the other with it down and the one with it down ran out of gas 40 miles sooner than the other truck. It surprised them so they built a water tunnel model to see what was happening. Basically with the tailgate up the air gets trapped and spins causing a cushion of air to form. With the tailgate down the air comes off the cab and pushes down on the tailgate causing more weight/drag.

 

You really need to go back and actually watch the whole episode egain.

They used Expys, not F150s.

They drove the track at only 45 mph. With exactly 5 gallons of fuel in each (they were emptied first), the truck with the A/C off and windows down went 30 miles further than the one with the A/C on and the windows up.

At this low speed, the drag from the open windows, IMHO, was not very significant while the drag from the A/C was constant. It is my suspicion that it the test were to be re-run at typical highway speeds of 65-70 mph, the difference would not have been anywhere near as significant since we all know these things have all the aerodynamics of a concrete block. A solid block vs one with holes in it would show significantly different drag coefficients in a wind tunnel.

Also, to have a more valid test, the test should have been repeated with the roles of the vehicles and drivers reversed to see if there was a variance between the vehicles and the drivers.

Entertaining? Yep.

Scientifically valid test? Only under the very restricted test conditions.

Steve

 

My '99 gets about 15.5 with or without A/C. It's 2WD and I'm around 75 MPH most of the time.