MGL Avionics Stratomaster MAXI Single E1

A capable engine monitor was hiding in the bargain bin.


It doesn’t take much to bring a homebuilt project that was progressing nicely to a grinding halt. In my case, we were nearing completion on my Zenith Zodiac 601 XL.

Through a combination of calibration errors and an undiscovered wiring error, the fancy-shmancy engine monitor that had been specifically built for my Corvair conversion powerplant was simply not to be believed. First, there was no tachometer indication. Next, the purported fuel pressure was about half of what was required to safely launch. And oil pressure during runup was shown as 27 pounds, well under the normal mid-40s we had witnessed on the test stand.

As the engine monitor display and remote CPU were removed for the second time, and shipped back to the manufacturer for recalibration and troubleshooting, we were stuck. Without reliable engine monitoring, that first flight wasn’t possible. We were running out of time.

Salvation came in the form of the inexpensive Stratomaster E1 engine monitor from MGL Avionics to use in the meantime. Just one in MGLs line of Maxi Singles, the E1 is designed to work with most engines from the light, two-stroke variety to conventional four-cylinder Lycoming or Continental aircraft engines.

The Maxi Singles are designed to drop into a standard 3.125-inch round instrument hole, and the smaller Smart Singles fit into 2.25-inch holes. Both of these instrument lines have a similar appearance, feature monochrome LCD displays, and are intended only for Experimental aircraft because they’re uncertified. Not having the burden of certification costs is reflected in the product lines retail prices; the E1 lists for just $220 (not including probes). I had spent nearly that amount for a pair of probes and round gauges from Mitchell just to get a handle on actual oil temp and pressure the old-fashioned way.

Wow, Thats Cool

Frankly, at such a low cost, I didn’t expect much from the E1. But when the unit showed up at the hangar, I was surprised in several ways. First, it weighs only 190 grams (about 7 ounces), and doesn’t come with or need a remote brain box for signal processing. All of the necessary electronics are in the panel-mounted unit itself. Second, the MGL E1 uses stock standard D-sub style connectors, 9-pin for power and a few other functions, and 15-pin for EGT and CHT probe connections. Furthermore, both 9- and 15-pin connectors and wiring harnesses are included. The only other thing in the box was the operator/installation manual, which contained a mere 12 pages. Was it really sufficient to cover all of the bases?

As it turned out, it was. Given all of the engine functions that the E1 can monitor, I was expecting the setup to be more complex than it was. However sparse the manual first appears, it is straightforward and comprehensive. One surprise was the totally flexible nature of the E1; it can be tailored to a wide variety of engine installations, be they air or water cooled, two or four stroke, with various numbers of cylinders. Its all selected in the logical, menu-driven setup, controlled by four simple buttons at the bottom of the unit.

Another surprise was the fully programmable alarms for each of the data channels, which can be set to trigger at both upper and lower limits. The first alarm level is visual, flashing the display of the parameter that is beyond programmed limits. A second alarm level can be selected to trigger an idiot light or aural alarm transducer. Pressing any of the buttons acknowledges the alarm and turns off the external lamp or buzzer, leaving the display to flash until the parameter is back within range.

There’s even a specific menu selection for the Rotax 912/914 series, which pre-assigns the alarm toggles for this engine. (No doubt here as to which powerplant the E1 designers had in mind when they created this engine monitor.) Another nice touch is the built-in Hobbs meter function, which can record engine time in hours and hundredths of hours and minutes. Do you already have some time on the mill? No matter. The Hobbs can easily be preset to match engine time already gone.

Heres Looking at You, Kid

The 2.5-inch (diagonally) liquid crystal display (LCD) has a limited amount of real estate available for displaying engine parameters, but it is well thought out. The display has a yellowish backlight that can be toggled off or on, and the contrast can be adjusted as well. The black letters and digits show up nicely against this slightly yellow background, no matter what the ambient lighting condition.

The tachometer is displayed by a horizontal bar graph along the top, and by a numeric readout in the upper right corner. When the engine isn’t running, and no tachometer input is detected, the digits change function to show Hobbs time and the bar graph disappears. The majority of the remaining display area is devoted to up to six engine parameters, the combination of which is selected during the initial setup process. You can have four CHTs displayed, or four EGTs or two of each. Or you can choose a single CHT and a single EGT. Once you’ve decided how to arrange the mix of CHTs and EGTs, you can select between displaying oil temperature and oil pressure or coolant temperature.

Installation Elation

After tearing my hair out while making repeated attempts to get the other engine monitor to function properly, Ill admit to not being in the best frame of mind to install yet another one. But my mood gradually got better as I went through the straightforward installation and setup procedure outlined in the manual. Connecting the new wiring harnesses to aircraft power and the existing probes was a non-issue, though I did need to change the oil temperature sender to the LM335 variety (available from MGL), and the J-type CHT probes to K-type.

Fortunately, KS Avionics of Hayward, California, builds both J- and K-type probes for many of the major engine monitor manufacturers, and is also familiar with the specific requirements of pre-threaded CHT probe wells found on Corvair cylinder heads. A slight reduction of probe spring length and a bit of rethreading is all that KS needed to do to one model of its stock probes for a perfect fit in the Corvair.

The E1 also needs to be told how many tachometer pulses per revolution to expect before it can display rpm properly, and with the Corvairs six four-stroke cylinders, this works out to three spark-plug pulses per crankshaft revolution. The good news was that this is one of the E1s stock menu options, but the bad news was that my Corvair was already set up with a ring gear tooth counter, and this isn’t one of the choices on the E1. So I ended up making an inductive pick-up out of a coil of safety wire that wrapped around the ignition coils primary lead and produced a nice 5-volt pulse with each spark. This drove the tach input on the E1 nicely.

After quickly setting up the alarm limits for CHT, EGT, oil temperature and oil pressure, I started the engine and was shocked to find that I now had accurate engine indications for the very first time. Best of all, we could get on with the high-speed taxi tests and test-flying.

Yes, There Are Limitations

Unlike the much higher-priced competition, the E1 has no data logging capability, no color-coded LEDs or bar graphs, and is limited to four channels of CHT or EGT readings, but not both. Further, there’s also no ability to monitor fuel pressure, which would be handy in my case. However, the E1 does several things exceedingly well. Its easy to install and set up, is extremely accommodating of different engine types and is lightweight. It runs on any DC voltage between 12 and 40, and draws very little current (90 milliamps with the backlight on, only 30 milliamps with the backlight off). With a list price of only $220, the E1 is an absolute winner in the bang for the buck arena. Even better, it works like a champ.

For more information, call MGL Avionics at 877/835-9464, or visit
For more information on KS Avionics, call 800/346-4469,
or visit


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