Instrumentation for Better Fuel Economy

Whether your reasons are financial or environmental, fuel economy seems to be a big deal these days.  Cruising for great gas mileage means fewer trips to the pumps, less mechanical wear and tear, reduced air pollution and, of course, saving money.

For some folks, getting a newer, fuel-efficient car is the answer.  But for many, getting a more efficient vehicle is not yet in the budget.  So, what can you do?

  • First, learn some basics about fuel economy, basic driving tips, hypermiling, ecomodding, etc.  I posted an introductory slideshow on it awhile back (it’s geared towards college students, but youl get the picture).
  • Next, visit my post on warm season driving tips.  Learn the tricks of A/C use, parking in the shade, NEVER idling.  By ‘adjusting the nut behind the wheel,’ you can tighten up your driving habits and maximizegas mileage for your vehicle.
  • Another tip is to consistently check your fuel economy.  Every time you fill up, keep track of your mileage, gallons of fuel, and cost.  You can keep a spreadsheet that tracks your fuel economy and cost.  Or, you can manage your fuel log online for free at a place like

Finally, invest in a real-time fuel economy (FE) gadget.  Knowing your fuel economy as you drive is a perfect training tool (which has already been incorporated into many newer cars (like the Toyota Prius–The Prius Effect).  I recommend the ScanGauge, which is compatible with most vehicles 1996 and newer with OBDII ports.  OBDII ports are usually located under the dash; a mechanic typically reads trouble codes through this port.  The ScanGauge plugs right in and provides several functions for you.

  • Digital display for multiple sensors (Coolant temperature, intake air temp, battery voltage, speed, RPM, etc.)
  • Calculates and displays fuel economy (instant FE, FE since engine start, FE for the tank, Gallons used per Hour, etc.)
  • Reads and clears trouble codes

Case Study: 2007 Pontiac Vibe (automatic)

BEFORE:  When I first got the Vibe, I was getting 26-28 MPG in town, and up to 33 mpg on the highway.  I was hitting the EPA estimate without any issue (and doing better than the new MPG calculation).  I was very impressed.

But in 2009 I found and and discovered what I was missing.  The first bit of advice almost everyone there gave was to invest in a ScanGauge.  Mine was about $150…which made me wonder if I’d ever get a ROI.

I installed my ScanGauge II in a cubby of my Vibe to hide it  (don’t want folks thinking it’s GPS and break in).

Now you see it, now you don’t!

AFTER: Since then, I’ve improved my fuel economy significantly.  Even around St. Louis with mixed driving/traffic, I’m averaging about 30 mpg per tank!!  I’ve hit highs of 38 and 40 mpg (per tank) on several occasions.  So, I’ve more than paid for my ScanGauge.

Why does the Scan Gauge help?  Because the real-time feedback trains me to monitor and adjust my habits.  It also becomes a bit of a game to compete with yourself.  I’m always trying to beat my best tank FE.  Best of luck to you!


7 thoughts on “Instrumentation for Better Fuel Economy

  1. Hi Mark
    Can you describe how you use the ScanGauge and what information is providing the feedback?

    I drive a Prius and use its display (the Hybrid System Indicator) for feedback. There’s some simple rules about where the indicator is along the line and what that means for efficiency.
    Some old cars had a vacuum gauge, which gives reasonable feedback too.

    The hardcore hypermilers use a ScanGauge on Prii, so I’ve always wondered what secrets the SG reveals to them.

    • Right. So anything with a sensor can generally be displayed digitally on the scangauge through the port. However, to calculate fuel economy ( instantaneously, per trip, per tank, etc.), it uses sensor data along with inputs provided by the driver. The driver specifies the engine size and fuel tank size first off. At the first fillup after installation, go through the fillup menu prompts without adjusting the estimated values (it will try to guess fuel use based on initial inputs). Going through the tank fillup menu will reset the internal trip and allow for more usable fuel data for the next tank. At the next fillup, the SG be calibrated for accuracy. Once it’s calibrated, it gives fairly accurate FE data.

      I have also heard vacuum gauges can be effective for older vehicles.

      Thanks for visiting the blog!

      • Thanks Mark
        I have a Garmin ecorouteHD that attaches to the OBDCII port. It gives me some of the information the ScanGauge can provide on spiffy-looking dials and I can record fuel purchases too. At the end of a trip it displays fuel used and is more accurate and realistic than the Prius’s optimistic HSI display.

        I guess I meant was, what instant feedback do you get from the SG and how do you adapt your driving to suit? Or is it just that you are monitoring each tank fill and so are more aware of your fuel consumption and your driving has changed generally?

      • Oh, OK. Well, the SGII has a lot of options, but can only display 4 gauges at a time. I prefer to use Instant FE, LOD (% Engine Load), Coolant Temp (useful when monitoring ecomods like grille blocks), and intake air temp (same reason).

        Instant FE, once calibrated, is fairly useful to improve my driving style. The FE gauge sometimes reads high values (9999 mpg) which can indicate that the car has DFCO (Direct Fuel Cutoff). DFCO operates on my particular car between 35mph and 65 mph when I let off the gas (coasting!). The 9999 mpg might indicate engine off for hybrids.
        The LOD display is similarly helpful at different RPMs and speeds. The lower, the better.

  2. Nice for those with newer cars. I have an old (1988) 4WD Toyota with OBD I. I am looking into using a generic vacuum gauge to do the same thing. I’ve gotten as high as 38.9 mpg highway, and that is with full-time four-wheel drive but with a manual transmission. I’ll keep you apprised of my test findings as I go along.

    • Thanks for stopping by. Having a manual sure does help. Some of the folks on the ecomodder forum approach 38-40 in Pontiac Vibes (or the Toyota Matrix twins) with a manual tranny and a few ecomodifications.

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