System Types and Basic Components

The main component of a wet-sump system is the oil pump, which draws oil from the sump and routes it to the engine. After the oil passes through the engine, it returns to the sump. In some engines, additional lubrication is supplied by the rotating crankshaft, which splashes oil onto portions of the engine.

An oil pump also supplies oil pressure in a dry-sump system, but the source of the oil is located external to the engine in a separate oil tank. After oil is routed through the engine, it is pumped from the various locations in the engine back to the oil tank by scavenge pumps. Dry-sump systems allow for a greater volume of oil to be supplied to the engine, which makes them more suitable for very large reciprocating engines.

Oil Pressure and Temperature Gauge

The oil pressure gauge provides a direct indication of the oil system’s operation. Green indicates the normal operating range, while red indicates the minimum and maximum pressures.

The oil temperature gauge measures the temperature of the oil. A green area shows the normal operating range, and the red line indicates the maximum allowable temperature. Unlike oil pressure, changes in oil temperature occur more slowly. This is particularly noticeable after starting a cold engine, when it may take several minutes or longer for the gauge to show any increase in oil temperature.

Oil Filter

As oil passes through the oil filter which is a fine-mesh screen, dirt, sediment, and other foreign matter are removed and settle to the bottom of the housing. At regular intervals, the cover is removed and the screen and housing cleaned with a solvent. An oil filter (white canister) is shown in the image provided.

Oil Pump

Oil entering the engine is pressurized, filtered, and regulated by a pump driven by the engine. As oil enters the gear chamber, it is picked up by the gear teeth, trapped between them and the sides of the gear chamber, is carried around the outside of the gears, and discharged from the pressure port into the oil screen passage. The pressurized oil flows to the oil filter, where any solid particles suspended in the oil are separated from it, preventing possible damage to moving parts of the engine.

Oil Pressure Regulating Valve

An oil pressure regulating valve limits oil pressure to a predetermined value, depending on the installation. This valve is sometimes referred to as a relief valve but its real function is to regulate the oil pressure at a present pressure level. The oil pressure must be sufficiently high to ensure adequate lubrication of the engine and its accessories at high speeds and powers. This pressure helps ensure that the oil film between the crankshaft journal and bearing is maintained. However, the pressure must not be too high, as leakage and damage to the oil system may result.

Oil Cooler

Most general aviation aircraft are air cooled. However, the lubrication system also helps regulate engine temperature via an oil cooler similar to the one shown.