Why Don't You Have an Engine Monitor?

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I sometimes find it hard to believe, but lots of owners of large displacement engines don't have multi-probe engine monitors. Given what they cost—that's to say not that much—these instruments ought to standard equipment on two counts: fuel savings and safety.

In an era of $6 avgas, leaning correctly is a survival skill and you can't do that confidently without knowing CHTs and EGTs accurately. And whether you agree with it or not, lean-of-peak operation saves big on gas—probably enough to pay for the monitor in a year if you fly much.

The fine art of interpreting CHT/EGT multi-cylinder digital display indications has sometimes been accused of being akin to reading voodoo bones. That's to say there can be any one of a number of interpretations of just what the display is trying to tell you. There's a hint of truth to that claim, because it's possible for certain untoward indications on the display to have more than one possible cause.

OK, we can agree to disagree on this. But digital multi-cylinder displays have so much to offer that it's hard to see why anyone who can afford one chooses not to. If you figure the potential money saved over the life of an engine, they certainly can be justified financially. Moreover, the peace of mind you get from seeing that old friend reading happy engine thoughts does provide a measure of solace that all is well. If you're on the fence about an engine monitor, we've published a courtesy article from this month's issue of Light Plane Maintenance. Click here to have a look.

In that article, we explain some of the multiple interpretations that occasionally give rise to confusion.

Understanding the CHT and EGT indications is a good start, not only as stand-alone indications, but also how they may work to compliment each other. Consider that you can isolate individual cylinder problems, regardless of the cause, and there have been a number of engine saves from pre-ignition or severe detonation that have been credited to these displays setting off alarms of impending engine melt-down.

But it doesn't have to be dramatic to be meaningful. Long-term, low-magnitude damage can take place and be undetectable by any other means than a multi-cylinder display, but some effort at learning by the pilot is needed to maximize the utility of these devices. Check out the article to learn more.

Also in this issue of LPM, we look at fuel injection nozzles, turbo maintenance and bladder care—not yours, your airplane's fuel bladders. Check out the links in the article for more in LPM.

Kim Santerre is editor of Light Plane Maintenance.

Comments (11)

Why do I not have an engine monitor? Simple, unlike those who buy a Cirrus, or any new aircraft, or whom the AOPA thinks is the "future" of GA, I am but a simple middle-class American that is just able to keep my 40+ year old aircraft in the air safely on the budget I have.

An engine monitor, installed, is around $2.5K, money I just do not have, especially in these turbulent times, to sink into an engine monitor. Especially for the less than 100 hours a year I fly.

Posted by: THOMAS DAGER | September 22, 2008 7:40 AM    Report this comment

Fault? So someone chooses to fly a plane without an engine monitor and they are being foolish?

That is like saying anyone that is not flying behind glass, or without a 496, or any other modern technology is being foolish.

They are choices, of that you are correct, and my choice to own an aircraft for which I fly only 100 hours a year IS mine. What other choice do I have? Partners? Not happening....fractional? Not in my area, heck we do not even have rental aircraft at my local airport anymore.

It IS expensive to put in an engine monitor, period. I also do not have a BRS, or Garmin 530, my panel is scatter-shot, not even the standard six-pack, so should I spend ten's of thousands of dollars on them as well?

BTW, you state that it will pay for itself in fuel costs over 3-400 hours, that is of course if I run LOP. Does that mean I have to buy injectors too? Or are the ones I have good enough? Who knows, but that could be even more cost.

Posted by: THOMAS DAGER | September 25, 2008 6:59 AM    Report this comment

I also do not have an engine monnitor due to cost... for the same reasons as Tom. I could buy an engine monitor for $2500, or I could fly another 60 hours on the same money.

Rodolfo's has no idea of the cost structure behind Tom's flying, or mine. I perform my own maintenance, and use auto gas... my costs are substantially different than he is assuming. Blanket statements about the payback from an engine monitor, or the costs of owning, are unsupported.

Posted by: Dan MacDonald | September 25, 2008 8:56 AM    Report this comment

The beauty of USA is freedom of choice. All choices have resulting consequences. The cost of early top overhauls because not being able to monitor engine performance is a consequence...pay me now or pay me later. I chose a JPI 6 channel monitor for my E-225-8 Continental and am very happy with the investment. Setting ROP mixture and seeing even CHT/EGT readings tells me the engine is happy, and when not even, says the engine is not being allowed to perform efficiently. My last trip I tried LOP settings, not expecting to be able to do this with the PS-5C pressure carb. To my surprise, it worked and would not have been possible without the monitor to fine tune the mixture setting, and I do mean fine tune, less than 1/8 turn of mix control from just right LOP to rough running engine - lowest / highest CHT 300F /330F, EGTs 1400 plus. Avg fuel burn 10.2 gal/hr (no fuel flow meter so this is based on total gallons to fill up tanks) over 6.6 hr flights at 7K/9K alt(two legs) vs normally around 12 to 12.5 gal/hr. I saved ~$70 to $80 (@ $5+ per gallon) in gas on this one trip with LOP. Lets see, 100 hrs per year, that is $7K to $8K in savings...I think the monitor will pay me back this year. But even without LOP, peace of mind for knowing how the engine is performing is worth every cent to avoid early and costly top overhauls. Two new jugs avoided pays for the monitor.

Posted by: Andrew Hesketh | September 25, 2008 9:57 AM    Report this comment

Because this is still the USA and a free country. As such, I don't want one. My money is better spent on keeping the engine pristine, radios working to optimum, and making sure the navigation systems are pin-point spot-on. I also prefer to keep my actual flying skills honed which I consider more valuable than another "Star Wheel". You do what you wish... AND I won't belittle your choice(s) until they affect me.

Posted by: David Spencer | September 25, 2008 12:13 PM    Report this comment

Also, right or wrong, I run 65% power and "Rich of Rough" and my single EGT shows that I'm slightly lean of peak. At such a low power setting the engine will not be damaged across a wide mixture range. I question if I would ever be able to pay back an engine analyzer investment on fuel savings.

I would really like an analyzer to help determine plug problems, valve problems, etc... If the instrument cost $500 I'd buy one!

Yet, somehow my plane has survived 50 years without one, hopefully it will go a few more.

Posted by: Dan MacDonald | September 25, 2008 1:28 PM    Report this comment

I have saved lots of money with my GEM 602. The best experience I have had with it was noticing a blockage in the injector of #5 cylinder on takeoff with the wife and kid in the plane. An hour later after climbing at reduced power and higher airspeeds I arrived at a mechanic friends airport. He had for years talked of LOP operation as a fools game and thought a multiprobe monitor was a stupid purchase as you should just run rich all the time. Imagine his surprise when I rolled up and told him to clean #5 injector. 5 minutes later we blew out a small piece of metal that was causing the blockage. If I had not had the monitor I would have burned up #5, as on takeoff it was running near peak EGT and the cylinder temps were headed up like a homesick angel.

Posted by: Brad Vaught | September 25, 2008 3:05 PM    Report this comment

Here I have to agree with Brad's point. Arguing fuel economics is missing the point. The real point is this: What is the biggest single value element in your plane? That's right, the engine. Unless you've installed one of those fancy Garmin glass panels in a Cessna 152, that engine is 40% or more of the value of the plane. Trend analysis of the running parameters of your engine is invaluable. Most of these devices will monitor and record parameters and analyzing it as important for an older engine as the EKG is for your heart.

As to safety, let me add my own story. I was running a Cherokee 6/260 (4 independent fuel tanks) on a long cross country with my wife and kids. I got into an argument with my daughter at the wrong time and lost SA on my fuel situation. Suddenly my JPI alerted me to wildly swinging fuel flows, with no other indications I began to notice a real incline in the Egt/Cht 'ladder.' As I pondered my display, combing my mind for the possible reasons why it would behave so, suddenly the plane became deathly quiet... Because I was thinking about the problem fully 20 to 30 seconds in advance, I quickly looked down and switched to the inboard tank. The engine lit off again in a matter of seconds. I lost only about 150 ft of altitude and 10 knots airspeed. Having that extra set of "eyes" on the engine, giving myself 30 secs of lead time on an emergency is worth is worth every penny. All the economics after that is pure gravy.


Posted by: Jeffrey Loudermilk | September 28, 2008 2:15 PM    Report this comment

Some people just don't want to know what Egt and Cht information can tell an owner! I my self am very interested in the info it will tell you, if you want to get more effienence out of your engine! Some people what to know this information.

Posted by: James A. Smith | September 28, 2008 11:34 PM    Report this comment

On 100 hours a year - it costs me $65 - $70 per hour to fly my 172 (including insurance, hangar rent, and engine reserves) Sure beats $100 an hour plus renter's insurance for our FBO's rental 172. I'm considering an engine monitor - it might save a couple of gallons of fuel, but I'm more interested in catching engine problems. Right now, I'm running a compression check every time I do an oil change (a $100 compression tester from ATS might not be as good as an engine monitor - but has done well catching problems early - and it's quick and easy to do)

Posted by: Josh Johnson | October 9, 2008 7:33 AM    Report this comment

After reading savvy aviator and pelican perch articles for 3 yrs and thinking about it, I decided a JPI should be added to the panel of my 1974 Bonanza .The engine overhaul was the perfect time and excuse to add it. It has been one of the best purchases I've made for my plane. I am convinced from the data I now get on every flight gives evidence as to why Continental engines are famous for requiring new jugs so often. I now know ALOT more about what is going on under the cowl during each phase of flight. It is surprising to know how dramatically things change during a trip.

Posted by: Timothy Hutchison | October 24, 2008 9:11 PM    Report this comment

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