Confession:  I am a data junkie.  Yes, all scientists are data junkies, but my particular dependency is much worse.  I have a Fitbit that monitors every step I take and every flight I climb; my bicycle has a computer to show me every bit of information about how fast and far I’m going; and there have been many other gadgets – smartphone, smartwatch, tablet -- to keep a stream of email and messages and news flowing to my brain.  It is ridiculous, I know, but like any junkie, I can’t help myself. 

Our motorhome is another giant gadget that feeds me a constant stream of data -- road speed, engine speed, fuel level, fuel economy, distance traveled, and my location on a colorful map.  Why is that not enough?  Because when I’m driving the motorhome, I am always making mental comparisons to driving my car.  They both have essentially the same engine – a 3.0-liter turbocharged diesel – and the performance of this clean-burning efficient engine was a key reason why I was excited about having a Sprinter chassis for our new motorhome.  But that 5-ton motorhome is twice the curb weight of my car; although that diesel engine has impressive torque, it’s clearly working harder, especially on grades and at freeway speeds. 

And that started me asking myself:  If the engine is working harder, what is the long term wear and tear on the engine components?  How much does our overall weight and engine load affect fuel economy?  Should I be driving differently to reduce the strain on the engine and improve its efficiency?  How is the engine affected by running the air conditioner, by driving up a mountain pass, or by extremes in outdoor temperatures?  The answers depend on gathering more data. 

That’s when I started reading about the ScanGauge, a popular device to monitor the parameters determining how well and how hard the engine is working.  It gathers these data from a wired connection to the vehicle’s standard OBD II port, which is the on-board diagnostics connector used by service technicians to access diagnostic data from all the onboard computers.  The alphanumeric output is displayed on a small illuminated LCD screen, which needs to be mounted somewhere on the dashboard.  

I like dedicated devices like this; after all, I have a Fitbit, a bike computer, etc.  But although the ScanGauge works well, I am not excited about its user interface.  Monitoring dynamically changing data, especially while driving, needs to be fast so as not to be distracting.  Analog dials, like the speedometer and tachometer on your dashboard, allow the eye and brain to more easily process real-time information; glancing at the position and movement of a needle is simpler than trying to interpret digits that are rapidly changing.

What I wanted was a better graphic interface for the engine data, and I already had a perfectly positioned large color display:  my oversized iPhone 7 Plus is always mounted just to the right of my steering wheel.  I decided to exploit this display and have the data stream wirelessly from a transmitter connected to the OBD II data port.  For the transmitter, I chose the Carista OBD adapter because it employs Bluetooth LE, a low energy wireless data protocol that is commonly used for smartphone interactions with fitness trackers and smartwatches.  The transmitter connects automatically (no passwords) to my iPhone and does not interfere with other Bluetooth operations, such as handsfree calling or music streaming to the vehicle’s sound system.  The wireless data stream of engine parameters is interpreted and displayed by the OBD Fusion smartphone app, which has a completely customizable graphics interface that is simple to modify.

The most important information I wanted to observe is the calculated engine “load”:  fuel economy starts to suffer significantly when this rises above 70%, and the Sprinter engine is straining if there is a sustained load above 80%.  By monitoring load, you can learn manual downshifting habits that put less wear on the engine components and improve the fuel economy.  I customized my iPhone screen to display analog dials for load, fuel rate, turbo boost, acceleration, battery charge level, and coolant temperature.  You can even flip between multiple dashboards if you need more information; there are some other readouts I would have liked to have (like oil temperature), but not all are available from the Sprinter's OBD II port.

The result was a nearly instantaneous readout that is easy to interpret at a glance while I’m driving (click on the screenshot to see a short movie of the app in action). There is significant battery drain from the constantly working display, but I typically keep the iPhone Lightning-USB cable plugged in anyway to power music streaming and GPS navigation.  The transmitter never had trouble connecting automatically to the phone once the engine was started.  The app can run in the background and did not interfere with phone calls (my iPhone uses the AT&T network) or any other phone operation.  The transmitter can also be easily unplugged and used in different vehicles, just like its companion smartphone.  Portability is especially practical because the transmitter and app can also be used to diagnose trouble codes from dashboard warning lights (like the dreaded and mysterious “Check Engine”).

I’m enjoying the displayed data stream as much as any gearhead would, though I still need to see if it meaningfully changes any of my driving habits – modifying when I downshift, how fast I accelerate, my speed on freeways or in hot weather, how I drive at high altitude, etc.).  The Carista transmitter plus the OBD Fusion app only cost $50, just 1/3 the price of a ScanGauge II, so this is not an expensive experiment.  But it will be interesting to see how long I actually use a real-time monitoring gadget to improve my driving.  After all, I used to wear a smartwatch, then decided it was too disruptive; I used to check my Fitbit throughout the day, and now I just look at it in the evening to see if I’ve earned dessert.  The benefit to fuel economy may be obvious sooner rather than later; the benefit to engine lifespan is probably something I will never know.

An updated version of this article was posted in early 2019, after testing a new device/app combination that accesses more onboard diagnostic/performance information, enables faster data sampling with more wireless security, and has an automatic sleep mode to avoid draining the chassis battery.