Preoiling reciprocating aircraft engines is usually necessary before starting a new or preserved engine, or one which has been idle for a period of time.

Using a preoiler (see figure 11-6) for reciprocating aircraft engines simplifies the job of preoiling. Such units supply preheated oil under pressure to the engine to ensure adequate lubrication before starting.

The conditions for preoiling turbine engines are essentially the same as those for reciprocating engines. In addition, if a lubricating oil line fitting has been disconnected on a turbine engine, the engine must be preoiled before starting again. The portable preoiler tank supplies low pressure oil to the lubrication system of the turbine engine.