Cool running

Do you remember the days before digital watches or clocks? When we were asked for the time, the answer usually would be something like “It’s almost 2:30″ or “About 1:15.” Then came digital timekeeping and the answers became “2:28″ or “1:13.”

When pilots began using Loran and ultimately GPS, the same thing happened with headings. What was “About 90°” became “089 is what I need for on course.”

I began flying in 1968, yet it took me exactly 30 years before I owned an aircraft with digital engine monitoring. Before then, it was the single point CHT gauge and EGT gauge provided by the factory that I used to manage my engines. For turbocharged airplanes, the EGT was actually a single-point Turbine Inlet Temperature (TIT) gauge that displayed the temperature of the exhaust gas just before it entered the turbocharger. Keeping the cylinder head and oil temps in the green and leaning by the single EGT gauge to not exceed the maximum allowed TIT was the norm and all my engines made it to TBO.

For the past six years I’ve had this digital engine monitor that displays the EGT and CHT for each of my engine’s four cylinders. The 30-year-old Lycoming Engine Operator’s Manual for the 30-year old engine (with 500 SMOH) in my 30-year old airplane says, “For maximum service life of the engine, maintain cylinder head temperatures between 150° F and 400° F.” Now that’s a range I can deal with! Red line for the engine is 475°.

However, modern day conventional wisdom dictates keeping the CHT from exceeding 380° for maximum engine life. So what was always “About 400° or a little less” per the factory single point CHT gauge was now regularly showing a digital 390° to 395° F on the hottest cylinder. On real hot days it might even nudge 400. Where the typical “in the green” reading used to be OK with me, comparing that reading (I still have the factory gauge) with the digital reading for the same cylinder (the number 3 cylinder, which is the hottest) made me squirm when it went over 380°, which happened often.

Opening cowl flaps (and losing a couple of knots) or richening the mixture would lower the temps some on those impossible days, but I wasn’t happy about the need for those techniques. Surfing the extensive web site of the Cardinal Flyers Online (CFO) organization I belong to revealed a number of simple and inexpensive tricks I could try under the cowling with baffling and spacers to correct for some assembly issues that impeded cooling. But, of course, my engine didn’t exhibit those issues, so nothing to do there. Typical for me is to just go directly to the most expensive method and save the time.

However, this time I caught a break. Maple Leaf Aviation, of Brandon, Manitoba, Canada, (AircraftSpeedMods.ca) markets an exhaust pipe fairing. The fairing is made of fiberglass using a fire retardant resin. The claim is that the fairing helps reduce engine temperatures by decreasing turbulence around the exhaust pipe. The theory is that turbulent air around the exhaust pipe goes into the cowling through that gaping cutout for the pipe and hinders the smooth airflow of the cooling that goes in from the front inlets of the cowling and escapes out the bottom rear of the cowling. Maple Leaf claimed I’d see a 15° to 25° reduction in CHT, and possibly a 1 to 2 knot cruise speed gain. Applicable models are Cessna 172 I through S, 177 thru B, 177RG, 180 C and on, 182 C through R and 185s all models, so my Cardinal RG was a candidate.

I polled the readers of the CFO daily email digest, and not one of the owners who had one said it didn’t help with cooling. So I popped for the $280 and it arrived in short order, along with all the STC paperwork. My mechanic did a beautiful job with the install, making sure it was offset to allow for exhaust pipe movement caused by engine torque.

The results? It works. My CHTs are running about 20° cooler in the climb on average. In cruise I’m seeing 10° to 15° cooler, even with cowl flaps fully closed (no noticeable speed gain, however). I’m also able to be more aggressive in leaning to my favorite best power setting and not wasting any fuel for cooling. My hottest cylinder digital CHT reading has yet to exceed 379°. And this is a good thing — in this digital age, if it went to 381°, I’d probably be worried.

Guy R. Maher has been involved in aircraft sales and type-specific training since 1972. With more than 12,500 hours in GA airplanes and helicopters, he currently flies an IFR EMS helicopter, is an FAA Aviation Safety Counselor, and provides consultation and testimony on operational and safety issues for legal proceedings.

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