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Caring For Your Aircraft

Part II: All About Engine Monitors

During climbout, monitor the CHTs. If temperatures on any cylinders rise beyond what's listed as a safe value in the pilot-owner's handbook (POH) for your aircraft, you'll need to open cowl flaps, lower the nose, or reduce power to lower the temperature.

In cruise, the engine monitor allows much more accurate leaning than a single-probe EGT. The exact procedure varies (check your POH), but usually starts with the airplane leveled out, and appropriate cruise MAP and RPM set. A safe prelean mixture is set using fuel flow or a memorized EGT value on one cylinder, then a lean-assist mode is selected on the engine monitor. Slowly and steadily, lean the mixture until the monitor identifies the first cylinder to peak—which may not be the cylinder with the highest EGT. Once that's done, you can enrich the mixture to achieve a specified temperature reduction ("50 degrees rich of peak") for best power operation—or in some cases, you may have another option, operating on the lean side of peak.

WE ASKED YOU!

Lean-of-peak (LOP) operation is a controversial subject, and a full discussion is beyond the scope of this article. In brief, the major engine manufacturers discourage LOP because of the risk of fuel detonation, which can damage the engine. Proponents argue that if done properly, LOP actually results in lower CHTs, which should be easier on the engine than traditional best-power or best-economy operation, while reducing fuel burn by up to 40%. Some aircraft manufacturers, among them Cirrus, recommend LOP operation, typically at reduced power (65% or less). Check the POH to see what's recommended for your aircraft.

In descent, monitor CHTs to avoid shock cooling, in which cylinders cool too quickly. This is mainly an issue in high-powered engines. Some engine monitors offer alarm settings to alert you if cylinders cool too fast. The cure for shock cooling is to carry enough power to keep the engine warm, and use speed brakes, extended landing gear or flaps to keep your speed down.

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