At what temperature should L9 oil be preheated to for optimal performance?

L9 oil should be preheated to -15°F/-26°C for optimal performance because this temperature is recommended to ensure proper viscosity and lubrication characteristics in colder conditions. Maintaining the viscosity within the optimal range allows the oil to flow effectively, reducing engine wear and ensuring reliable operation of the Auxiliary Power Unit (APU) during startup and operation in low-temperature environments.

Choosing a higher preheat temperature could lead to sluggish oil flow, while a lower temperature might result in the oil being too viscous, causing inadequate lubrication and potential damage. Therefore, the specified preheating temperature of -15°F/-26°C strikes a balance that ensures the oil remains effective without compromising the APU's performance.