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Technique: Lean-of-peak engine operationsTechnique: Lean-of-peak engine operations

Keeping your cool on less fuel

Illustration by Charles Floyd
Click on image to enlarge.

The key to engine longevity and reliability is keeping CHTs from becoming too hot. Use a rich mixture setting, reduced manifold pressure, a shallower climb angle, or a combination to keep CHTs well below manufacturer limits at high power settings. LOP mixture settings can accomplish the same purpose in cruise.


There are two strategies for keeping cylinders cool in cruise: push the red mixture knob forward for a rich fuel/air mixture setting that uses unburned fuel to lower cylinder head temperatures, or pull the mixture knob out to such a lean setting that an abundance of air and reduction in engine power and heat cools the cylinders. Running aircraft engines “lean of peak” (LOP) typically reduces airspeed about 5 percent in cruise while lowering fuel consumption about 20 percent—but not all engines are capable of LOP operations, and doing it wrong can cause permanent and costly engine damage.

What equipment does your engine need to run safely lean of peak? It must be fuel injected (not carbureted), preferably with matched-flow nozzles such as GAMI injectors, and it should have a graphical engine monitor with cylinder head temperature (CHT) and exhaust gas temperature (EGT) probes on every cylinder. Electronic ignition systems are more efficient than magnetos and simplify LOP operations, but electronic ignitions aren’t required.

Dave Hirschman

Dave Hirschman

AOPA Pilot Editor at Large
AOPA Pilot Editor at Large Dave Hirschman joined AOPA in 2008. He has an airline transport pilot certificate and instrument and multiengine flight instructor certificates. Dave flies vintage, historical, and Experimental airplanes and specializes in tailwheel and aerobatic instruction.

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