For optimal fuel economy, how should the mixture be set?

Setting the mixture to peak exhaust gas temperature (EGT) is often considered optimal for fuel economy during cruise flight. At this mixture setting, the air-fuel mixture is achieving an ideal balance that maximizes the thermal efficiency of the engine. When the engine operates at peak EGT, it ensures that the combustion process is efficient, with the fuel being burned effectively, and this leads to better fuel economy, as less fuel is wasted.

Operating the engine at peak EGT means that you are using an appropriate amount of fuel that matches the amount of air entering the engine, which results in a cleaner burn and potentially extends the engine's life by reducing carbon buildup and other residues.

Other methods, like leaning until the engine coughs and then enriching the mixture, might risk causing engine roughness or performance issues before reaching the optimal mixture ratio. Leaving the mixture at peak EGT allows for sustained efficiency during flight, while following manual guidelines to set a richer mixture may not take full advantage of the fuel savings that can be achieved at the optimal peak EGT setting.