Functions of engine oil
Aircraft engine oil performs six main functions:
| Function | Description |
|---|---|
| Lubrication | Reduces friction between crankshaft, rods, pistons, camshaft |
| Cooling | Transports heat from the combustion area to the oil cooler |
| Cleaning | Suspends combustion residues and metal wear; filter captures them |
| Sealing | Seals the gap between piston ring and cylinder |
| Corrosion protection | Protects internal components from rust |
| Hydraulic actuator | Drives the constant-speed propeller pitch mechanism |
Oil system
Two basic configurations:
- Wet sump — oil collected in the oil pan under the crankshaft; simple, used in Lycoming/Continental.
- Dry sump — oil stored in a separate tank; more complex, found in aerobatic engines (inverted flight capability).
In-flight monitoring
| Instrument | Normal | Abnormal |
|---|---|---|
| Oil pressure | Stable in the green | Sudden loss = pump failure, oil loss → land immediately |
| Oil temperature | Rises after start to cruise value | Sudden rise = loss of cooling, possible oil shortage → reduce power, land |
Watch the combination: rising oil temperature with falling oil pressure is a serious indication of imminent failure → land immediately (see Subject 070).
Oil change
Typical intervals (AFM/Operator's Manual governs):
- With filter: every 50 h
- Without filter, with screen: every 25 h
- Mineral oil during break-in, then multi-grade synthetic or mineral oil per manufacturer specification.