At lunch the other day, we were talking about this group of people who call themselves "hypermilers." They get extreme fuel efficiency from regular cars by adjusting their driving style instead of by buying hybrids or messing with the engines. I read through a long article about this, and it got me excited about the topic again.

I've always wondered about my fuel mileage while driving.

  • What is the difference in fuel economy when I go 60 instead of 50 or 70 instead of 60? What is the most fuel efficient speed when I'm in top gear? Create a graph of mpg vs. speed.
  • How close do I have to be to a car or semi to get a draft off of them?
  • How much fuel do I waste having the windows down or the air conditioner on?
  • What does it cost me to have the roof rack on top of my car?
  • How much extra fuel does it use to have one, two, or three people in the car with me?
  • How much more fuel does it use to coast in gear versus coasting in neutral?
  • What change do I see if all of my tires are under-inflated by 1 psi? 2 psi?
  • If you have the windows down on the interstate, can you tell a difference in mileage when you stick your arm out the window?
  • What is the difference in a 0-40mph acceleration if I stomp on the gas or accelerate slowly?
  • How much gas does my car use to idle for one minute?

The list goes on and on. I know that computers and sensors exist to track this type of thing, but I always assumed they were way out of my price range. Without an instantaneous and constantly updating mpg readout, it's very difficult to conclusively answer these things. Even if they answer one of these questions on MythBusters, that doesn't settle it for me because they probably have slightly different conditions than I do (different car, etc.)

A quick internet search led me to ScanGauge. There are numerous products like it, but this one drew my attention and had a lot of good reviews. Best of all, it's very simple to install.

The ScanGauge hooks into your cars OBDII port and talks to your car's computer. Every car since 1996 has one of these ports, and it's what the car shop uses to scan your engine for trouble codes when the check engine light comes on. If this sounds familiar, you may remember that I started working on my own interface to the OBD2 port on my Mustang back in 2003 (posts here here and here.)

The ScanGauge gives you instantaneous readouts of many different sensors including fuel economy, fuel rate, coolant temperature, intake air temperature, engine load, manifold pressure, etc. It also will tell you the error code if something is wrong with your engine and let you clear the code once you've fixed it. Reading the codes usually costs $50-100 at the shop so this could potentially save some money.

This is also bound to improve my gas mileage. If I can get a 5% improvement in my mileage, this unit will pay for itself in just over a year.

It hasn't shipped from Amazon yet, but hopefully it will arrive sometime next week. I'll have another post where I answer some/all of these questions for you. If you have additional things for me to test, shoot me an email or leave a comment on this post. I'd love to have a nice big list of things to test. Maybe I'll even dress up as Jamie from MythBusters. Who wants to be Adam?