Not Flying Blind Anymore!

by Dave Weiman

EDITOR’S NOTE: Since this article was originally published in the August/September 2014 issue, it has been amended.  See amendment at the end of this article.

During the summer of 1981, a radical new instrument appeared in the Bonanza’s panel – a one-of-a-kind instrument. Bright orange bars of gas plasma climbed the display, constantly monitoring and instantly responding to every power stroke. The new instrument had a finger on the pulse of each cylinder, and demonstrated the ability to graphically depict the whole spectrum of powerplant operation. Never again would a simple problem like a fouled plug spoil the enjoyment of a flight, or would the mixture be leaned too much or too little, resulting in costly repairs. The world’s first Graphic Engine Monitor (GEM) had been invented by Insight Avionics and was unveiled at the American Bonanza Society convention that same year.

Many models later, the designers at Insight Avionics continue to combine a thorough understanding of aircraft systems, technology, and the cockpit environment with computer aided design and manufacturing (CAD/CAM) and computer numerical control (CNC) machining to craft instruments that are finely tuned to the needs of pilots.

My appreciation for Insight GEMs came out of necessity. With only 1200 hours since major overhaul on the O-470 Continental engine in my 1976 Cessna 182 Skylane, I had to replace three of six cylinders, which made me concern that after 27 years of flying the plane, I might be leaning the mixture incorrectly. Like most, I was taught to lean until the engine began running rough, or I saw a decrease in RPMs, then add at least an inch or more of mixture. I also added an exhaust gas temperature (EGT) gauge about 10 years ago, so I thought I had the bases covered.

I referred to my pilot’s operating handbook (POH) to make sure I was maintaining the correct power settings, cowl flaps, airspeed and angle of attack on climb-out to keep the engine cool, and applied carburetor heat when needed.

I also asked the advice of maintenance professionals and got a mix of feedback.

One mechanic told me not to worry about it… “just fly the plane,” he said. Another mechanic told me that Continentals were notorious for going through cylinders, but had strong bottoms, so I could likely go beyond TBO, but would continue to replace cylinders – still not a cheap option. About then I began longing for my generally trouble-free 150 hp, four-cylinder Lycoming O-320 in a 1974 Cessna 172 Skyhawk I once owned, but everything is a tradeoff. With the 182, I have more power, more payload, greater range, and it is a more stable instrument platform, but the 172 was more economical.

Darrell Bolduc of Bolduc Aviation at Anoka County/Blaine Airport in the Twin Cities, overhauled my engine more than a decade ago, and has replaced the cylinders as needed. It was Darrell who reminded me that my original cylinder head temperature (CHT) gauge only gave me the temperature of the coolest cylinder, so I did not know whether or not the other five cylinders were cool or running hot. Therefore, despite my effort to keep my engine cool, I was flying blind when it came to “leaning” the mixture, not knowing the temperatures of each cylinder.

To correct this, Bolduc recommended that I install a Graphic Engine Monitor (GEM) so I would know from startup to shutdown the temperature of each cylinder and could accurately adjust the mixture to keep the engine cool.

I called around and landed at Gran-Aire, Inc. ( at Milwaukee Timmerman Airport (KMWC) in Milwaukee, Wisconsin. Chief aircraft technician Gary Bavuso had installed a lot of Insight Avionics engine monitors, and is convinced that they are one of the best manufacturers in business today. Insight monitors are also relatively easy to install, rarely need maintenance, and are a great value. JPI was the other option, which also receives good reviews. Based on Bavuso’s experience installing Insight Avionics monitors and their lower cost, I chose the Insight “G4.”

Additional features of the Insight G4 include a comprehensive data log/windows file stored on a removable Secure Digital (SD) card, so data recorded over time can be reviewed after engine shutdown; over-the-web software updates; Spectral Vibration Analysis; exhaust valve analysis – EGT Variation Spectrum; and an integral fuel computer with GPS fuel interface.

The G4 will operate standalone, or can interface with other data sources and report information to other instruments like multi-functional displays (MFDs) and my Garmin 430s.

Installation costs can vary depending on the amount of time it takes the technician to do the installation (that’s where experience installing a particular GEM pays off), and the features you add, such as “fuel flow,” which was one feature I definitely wanted.

The G4 has the larger 3.125-inch bezel (instrument face) size, making it easy to see. In comparison, the lesser expensive G3 has a 2.25-inch bezel, but provides the same amount of information.

Positioning the monitor in your panel is extremely important, as you will be looking at it more than you might think. Bolduc encouraged me to position the monitor as much directly in front of the pilot-in-command for that reason.

I chose to have the monitor mounted just below the Course Deviation Indicators (CDIs) or VORs. A little lower than I wanted, but I already had a 3.125-inch hole in my instrument panel, and it was my best option. To compensate for the slightly lower position on the panel, I simply lowered my seat a tad.

Tanis Aircraft Products continues to offer independent systems and upgrade solutions that heat all the cylinder assemblies and the entire engine without interfering with engine monitor installations or operation.

If you currently have a Tanis preheat system that uses CHT wells for heating cylinders and you are installing a monitor, simply upgrade to the rocker cover/intake tube threaded element.

Tanis has STCs for both four (4) and six (6)-cylinder Continental, Lycoming, and Franklin engines (

The G4 is a sophisticated tool for engine management. Its microprocessor performs many tasks that used to be handled by the pilot.

One of the basic functions performed by the G4 is monitoring exhaust gas temperatures (EGT) for each cylinder with one-degree resolution. What is important is the EGT of a particular cylinder in relation to its peak. But peak EGT is not a constant; it changes with atmospheric conditions, altitude, power setting and engine condition, and for this reason, absolute exhaust gas temperatures in degrees Fahrenheit are quite meaningless.

The real objective of mixture management is finding a mixture setting, which represents the correct position on the EGT/Fuel Flow Curve. This abstract task is easily accomplished by the G4’s microprocessor, which samples EGTs for all cylinders many times a second and subjects this data to a complex mathematical analysis that can identify peak EGT. This capability allows the pilot to operate the aircraft engine at the most economical mixture settings, and at a setting that will ensure proper engine cooling.

The Graphic Engine Monitor (GEM) is ready to operate the moment electrical power is applied. Within seconds after starting the engine, the white EGT bar graph columns will begin to appear on the monitor. Each column corresponds to the EGT of a particular cylinder. The lowest EGT that can be displayed by the G4 is 800° F.

In some engines, the throttle will have to be opened to the fast idle range to get an EGT indication for all cylinders. As the cylinder heads begin to warm up, the display will indicate cylinder head temperature (CHT) for all cylinders as a smaller green bar graph column in each EGT column. A horizontal red line across each column represents the maximum allowable CHT.

The EGT and CHT bar graphs are interpreted much like a conventional mercury thermometer…the higher the bar, the higher the temperature.

Since EGT is normally higher than CHT, the green bar which represents CHT is on top of the white illuminated EGT bar and stands out clearly.

Digital numbers below each bar graph column indicate the exact EGT (four-digit) and CHT (three-digit) temperature for each cylinder.

Should an EGT probe fail, the entire EGT column for that cylinder will go blank, and the numeric indication will appear as dashes, but the CHT bar will still remain green. The failure of one probe will not affect the display of any other probe.

On the probe diagnostic page, it shows the current probe resistance. If the probe has unusually high or low numbers, we know there is a problem. If the numbers are low or “closed,” something may have shorted out to the ground or to another component, or a circuit has no resistance. If the numbers are high or “open,” a circuit does not complete, and there may be a broken wire or terminal. All of this information is very helpful to the aircraft technician when verifying a fault.

Operationally, there are two control knobs on the G4 that operate a combination of rotary and push button switches. The top knob in general controls screen selection, while the bottom knob controls items within the given screen. Each screen assigns its own functional needs to the controls that may change depending on context. A screen may also label the controls with guidance information like “Push To Exit.”

The G4 is designed to expand and grow with the times.

Simultaneously, EGT, CHT, Turbine Inlet Temperature (TIT), Manifold Pressure (MAP), Tachometer (RPMs), Carburetor Temperature (CARB), Outside Air Temperature (OAT), Oil Pressure (OIL), Bus Voltage (VDC), Fuel Flow (GPH), fuel used, alternator temp, oil temperature, and instrument vacuum, can all be monitored.

The color-coded bar graph and digital values featured on the Insight G4 may be “primary” for EGT, CHT, and TIT. That means if your original engine instruments die, the CHT, EGT and TIT features on the Insight G4 can be used to replace them, saving the aircraft owner the expense of replacing them. All other data shown in cyan at the top of the display are “supplementary.”

Leaning of The Mixture

Some pilots choose to lean their mixture “lean of peak,” while others like me, prefer to operate “rich of peak.” Based on information I have received from Insight Avionics and a variety of other sources, this is the procedure I follow when leaning my Continental O-470 “rich of peak.” (Readers are urged to likewise consult with Insight Avionics and their engine and aircraft manufacturer, and refer to the owner’s manual and DVD that come with each system.)

I take off at full rich at full power at or near sea level. Upon reaching the desire altitude, I level off and come back to approximately 2300 RPMs and between 15 and 23 inches of manifold pressure (MAP), depending on my altitude. The Insight G4 depicts both the Tachometer (RPMs) and Manifold Pressure (MAP) digitally, so there’s no guessing as to the accuracy of your settings.

I then push and hold the reset button, located on the lower right-hand side of the monitor, for 3 seconds to erase the temperature difference boxes prior to leaning, and once I reach peak Engine Gas Temperature (EGT) displayed in a box above each cylinder column, I press the reset button again for 3 seconds before enriching the mixture. (Reverse mixture control motion to enrich the mixture to obtain the fuel flow rate or EGT drop recommended by the engine and airframe manufacturer.) The EGT drop is continuously displayed above the EGT column. You know you have reached the desired EGT drop when the temperature box turns from hollow to solid.

Temperatures depicted when leaning lean of peak are “hot,” or degrees hotter than peak temperature, and the temperatures depicted when leaning rich of peak are “cool,” or degrees cooler than peak temperature. Lean temperatures are depicted in “black and white,” preceded by the letter “L,” and rich temperatures are depicted in “cyan,” preceded by the letter “R.”

I operate each of my six cylinders between 100 and 125 degrees Fahrenheit rich or cool of peak, and no less than 75 degrees rich or cool of peak. Normal cylinder temperatures (CHT) for the O-470 is between 200 and 460 degrees Fahrenheit, ranging from 297 and 387 degrees on one recent flight at 5000 feet MSL, with an EGT between 1309 and 1469. The outside temperature that day was 7 degrees Fahrenheit, and I was consuming 14.7 GPH. Again, consult with your engine and aircraft manufacturer to determine the best operating range for your aircraft, and keep track of your temperature ranges.

Besides knowing your numbers, as an owner/operator (not an expert), I feel it is important to look for consistency between bar graphs and temperature readings. If one cylinder is acting differently than the other cylinders, I am going to consult with my aircraft technician immediately. Without the engine monitor, I would likely not detect a potential problem.

The G4 buss voltage attempts to display the buss voltage in green when it is normal and red when it is outside of normal. In an aircraft with a 12V electrical system, the buss voltage will be annunciated in green so long as the voltage is 12.0V to 14.9V (inclusive).

In an aircraft with a 24V electrical system, the buss voltage will be annunciated in green so long as the voltage is 24.2V to 28.7V (inclusive). Below this range, the alternator is not charging the battery, and above that, it is overcharging, and the buss voltage will be annunciated in red.

For additional information on Insight Avionics and the complete line of graphic engine monitors for single-engine and twin-engine aircraft and helicopters, go to or call 905-871-0733 or email

ADDITIONAL REFERENCES: For installation contact Gary Bavuso, Gran-Aire, Inc: 414-461-3222, ( For engine rebuilding and repair to factory zero-time specifications, contact Darrell Bolduc, Bolduc Aviation Specialized Services: 763-780-1185, ( For aircraft preheat systems, contact Doug Evink, Tanis Aircraft Products, Inc: 800-443-2136, (


Peak Is Peak, Other Temperatures Are Cooler!

In the feature article entitled “Not Flying Blind Anymore!” (Midwest Flyer Magazine, August/September 2014, page 26) which describes one pilot’s experience in using an Insight Avionics G4 Graphic Engine Monitor, there needs to be a correction pertaining to Exhaust Gas Temperatures (EGT).

The article states:

Temperatures depicted when leaning lean of peak are “hot,” or degrees hotter than peak temperature, and the temperatures depicted when leaning rich of peak are “cool,” or degrees cooler than peak temperature. Lean temperatures are depicted in “black and white,” preceded by the letter “L,” and rich temperatures are depicted in “cyan,” preceded by the letter “R.”

Based on reader input, the article should be corrected to state as follows:

Exhaust Gas Temperatures (EGT) depicted when leaning lean of peak is measured in degrees “cooler” than peak EGT, at a leaner or lower fuel flow than the fuel flow was at peak EGT.

Exhaust Gas Temperatures depicted when leaning rich of peak are also “cooler” than peak EGT, though at a richer or higher fuel flow than the fuel flow was at peak EGT.

Lean of peak temperatures are depicted in “black and white,” preceded by the letter “L,” and rich of peak temperatures are depicted in “cyan,” preceded by the letter “R.”

Additionally, in aircraft with a 24-volt electrical system, the buss voltage will be annunciated in cyan (not green as stated in the article), so long as the voltage is 24.2 to 28.7 (inclusive). Below this range, the alternator is not charging the battery, and above that, it is overcharging, and the buss voltage will be annunciated in red. End article amendment here.

NOTE: Once you find where the peak EGT is, do not spend a lot of time in that peak EGT zone, especially at high power. Once you find where the peak temperature is, you want to run either lean of peak for air-cooled fuel injected engines, or rich of peak using fuel for cooling carbureted engines.

CAUTION: You do not want to approach the maximum EGT as defined by the manufacturer for more than a few seconds. General Aviation Modifications, Inc. (GAMI) calls this the “big pull,” and “avoid the Red Box.”

EDITOR’S NOTE: The information provided here or elsewhere in Midwest Flyer Magazine is based on limited observations by one or more pilots, operating one or more aircraft, and should not be relied on as technical advice or recommendations for any other aircraft. Readers are urged to refer to the owner’s manual and DVD that come with each Insight Avionics graphic engine monitor, their aircraft operator’s handbook, and their engine manufacturer’s operation guidelines, and consult directly with Insight Avionics (, General Aviation Modifications, Inc. (, and other technical sources.

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