Saturday, December 9, 2023


Use an engine monitor to drive safer and cheaper

By Greg Illes

In 1996, the U.S. auto manufacturers began adhering to (another) new standard. This time it was the Onboard Diagnostic Port, or OBD interface to the engine electronics. This port (since evolved to OBD-2) allowed access to a host of engine parameters, from water temperature to fuel flow and other critical operating numbers. The OBD also reads the CEL (check engine light) fault codes that help mechanics diagnose engine troubles.

These units are sometimes referred to as “engine monitors,” and they do exactly that, with programmable displays for parameters of concern. One such product is the Scangauge, available in a variety of models and capabilities for about $130. But why would anyone want to look at OBD information as long as their engine was in good health? There are a few good reasons.

Perhaps the most useful information available from OBD is fuel mileage. The Scangauge unit provides both instantaneous and average mile-per-gallon numbers, so you can immediately see the effect of your driving techniques on fuel economy. Rather than waiting for a tank refill to get an idea of your average consumption, you can watch the numbers rise or plummet as you negotiate hills and headwinds. It’s also possible to watch the gauge and seek out which throttle and gearing combinations provide the best fuel economy.

Today’s “idiot light” panels often won’t tell you about an engine parameter until it is out-of-bounds. Furthermore, some truly important information, for example transmission oil temperature, is not gauged or error-lit in most vehicles. The engine monitor can provide information which could only be had by installing an entire separate dash gauge.

With numerical information on water temperature, transmission temperature or what-have-you, it’s possible to see a negative trend and take appropriate action before you’re stranded. You can also see “197F” instead of the too-simplistic L — H indicator.

Installation is simplicity itself. All information and power come from the OBD port. Plug in the unit, find a place to mount it with its Velcro stickies, and that’s it.

The bottom line is that an engine monitor will let you get the best mileage from your rig and will enable you to see and manage the health of your engine operations. Why would you NOT want to do this?

Greg Illes is a retired systems engineer who loves thinking up RV upgrades and modifications. When he’s not working on his motorhome, he’s traveling in it. You can follow his blog at



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