Engine oil is vital to aviation because it prevents friction, which would otherwise bring excessive wear, overheating and eventual failure. Aircraft engines, especially air-cooled models, contain crankshafts and connecting rods working under intense stress, and only a continuous lubricant film lets them survive these loads hour after hour.
Designers size the usable oil tank so that endurance under the engine's most demanding operating condition multiplied by that same condition's maximum oil burn, plus an added circulation margin, is never exceeded. A gas-turbine exhausts far less oil than a piston unit, and a typical Cessna 172 might use one quart every 8.1 flight hours, while some engines are even lower at 0.08 quart per hour.
Burn rate is not constant, however, because consumption over an oil-change interval is non-linear and is influenced by engine condition, flight time and other operational factors. Thus pilots must track the level and service the system before any planned sortie.
Expert behind this article
Jim Goodrich
Jim Goodrich is a pilot, aviation expert and founder of Tsunami Air.
What is the role of oil in an airplane engine?
Inside every aircraft engine, oil is the lifeblood of the engine. Oil lubricates moving parts, cushions moving parts, and reduces friction. Oil forms a seal between the piston and the cylinder wall, preventing leakage of the gases from the combustion chamber and sealing them.
Oil manages heat. Air-cooled aircraft engines burn oil because they use oil as a primary cooling medium. Oil draws heat away from cylinder heads, cylinder walls, and bearing surfaces on the crankshaft. Oil cools the engine by reducing friction and reduces heat produced by moving parts. Oil suspends by-products produced by the combustion process, collects soot and debris, and removes contaminants. As engine oil is burned, it must be replenished.
The oil system supplies oil under pressure. The oil pump circulates oil from sump to engine, pumping oil from the sump and routing it to the engine, especially in wet-sump systems. In dry-sump systems, a scavenge pump returns oil from engine to oil tank, while a separate reservoir contains oil in a separate tank. Large volume, dry-sump systems allow a greater volume of oil to be supplied to the engine. Oil system gauges monitor oil pressure and temperature, reporting possible malfunctions like low/high oil pressure and temperature.
What are the benefits of oil in an airplane?
The benefits of oil in an airplane are explained below.
- Oil ensures moving parts stay functional and efficient under heavy loads.
- The correct type of oil ensures aircraft operate safely and efficiently.
- Oil helps protect engine steel parts from rust during periods of disuse.
- Oil serves as hydraulic fluid for constant-speed propeller blade pitch adjustment.
- Oil provides sealant to prevent leakage past O-rings, gaskets, and various other seals.
- Oil helps maintain equipment equilibrium in aircraft.
- Oil keeps contaminants dispersed and holds them in suspension and carries combustion by-products away from vital parts.
- Oil protects moving parts under heavy loads.
- High-performance oil provides effective lubrication, heat dissipation, contaminant control and corrosion prevention.
- Oil analysis helps locate worn elements inside aircraft engines.
- Oil's corrosion inhibitors guard against rust.
- Oil can lower the octane rating of fuel if present in the combustion chamber.
Selecting the correct oil viscosity remains vital because viscosity affects oil's ability to lubricate and protect engine components. Better energy efficiency from quality lubricants saves money with every take-off and landing, while oil analysis provides an early warning system that monitors engine condition, detects worn elements and allows evaluation of engine data trends to prevent costly future repairs. Oil carries combustion by-products and blow-by contaminants away from pivotal parts, holding them in suspension until the next oil change when the additive package is replenished. Ashless dispersants in AD oil keep contaminants suspended so sludge does not accumulate on internal engine parts.
Oil performs lubrication, letting parts run smoothly and cutting the resistance the motor creates. It forms a coating that makes the reciprocating engine and its bearings work smoothly while the oil runs through the motor. The grease behaves as a coolant as it takes in heat and disperses it. Caloric administration is necessary for preserving motor state.
How often must airplane oil be changed?
The airplane oil must be changed every 25 to 50 hours of flight time, with the shorter interval reserved for engines that use only an oil screen. Operators who fly at least 150 hours a year can go 50 hours between changes, whereas those who fly fewer hours must shorten the interval proportionally. Owners who log 100 or fewer hours annually change oil at least four times a year - roughly every three months. Continental and Lycoming require oil changes every 50 hours or at most every 4-6 calendar months, whichever occurs first, when a full-flow oil filter is installed. If the engine lacks such a filter, the limit drops to 25 hours.
Service Bulletin No. 480 formalizes the 50-hour oil and filter replacement for all engines with full-flow filtration, while allowing a four-month maximum interval even for low-utilization aircraft. For frequently flown aircraft, many mechanics contemplate 30-40 operating hours - four or five changes per year - the best duration for balancing protection and cost. Engines operated in dusty environments or with high oil consumption from excessive blow-by need more frequent oil changes.
How to change the oil in an airplane?
Changing oil in an airplane begins with flight: you fly your airplane to warm the oil. Lycoming suggests waiting 15 minutes after shutting down the engine to begin draining the oil. Next, set up your area, place a container under the drain plug to catch old oil. You cut the safety wire holding drain plug. Tools needed include an appropriate size wrench for oil sump drain plug. Oil drains by gravity into the bucket through the hose connected from quick drain to bucket. You allow oil to completely drain before proceeding. For the filter side, first unscrew oil dipstick, which provides air gap to facilitate draining. You set the old filter aside. Install new oil filter, wipe gasket with oil, thread filter on until gasket touches engine block, then torque to 17 ft-lbs (23.0 Nm)/204 in-lbs (23.0 Nm) and secure with safety wire after installing the new oil filter. Put a new safety wire on the drain plug to finish the work. The manual determines appropriate oil type and quantity. ,Run the engine to check for leaking. Dispose of the old oil at a maintenance shop.
What is the oil capacity of an airplane?
The oil capacity of an airplane varies with the model. A Cessna 182 sump accepts a maximum of twelve quarts, yet the engine runs safely on six, while an Extra 300 with an AEIO-540 carries fourteen and the A320 overflow tank alone holds 20.1 qt. For most four-seat trainers approved under the old Handbook 107 formula, designers start by multiplying planned endurance by the highest published oil-consumption rate, then add a cooling-margin. A 1949 rule of thumb adds one gallon (3.785 liters) for every 25 gallons (94.635 liters) of fuel or, for non-transport pistons, one gallon (3.785 liters) for every 75 maximum continuous horsepower. Once the tank size is fixed, regulations demand that at least ten percent of that volume - never less than half a gallon - remain empty for froth and expansion, so usable oil is always less than total capacity. Owners therefore fill only to the placarded high mark, commonly eight quarts in an O-360 or seven quarts in a 182 sump, and never below the six- or nine-quart flight minimum printed in the POH.
How much oil does an airplane use?
The amount of oil used by an airplane varies. A Cessna 172 burns one quart of oil every 7.9-8.1 flight-hours, an average of 0.1 quart per hour. Fleet data show the same pattern for the C-182. The TCDS for turbocharged TSIO-520-BB engines states that maximum acceptable oil consumption is about one quart per hour, while jet engines are limited to one pint per hour. Operators therefore track make-up oil added between changes and divide by the hours flown. If the rate exceeds one pint per hour on a jet or one quart per hour on a piston engine, an oil-consumption run is required. Excessive consumption is treated as a symptom of an oil leak or impending overhaul.
A Boeing 737-800 uses about 2.5-3 tons of fuel per hour, an Airbus A320 burns around 2.5 tons per hour, a Boeing 777 consumes 7-8 tons per hour, and an A380 or 747-400 burns 10-12 tons per hour. Over a 10-hour mission a 747 burns 36,000 gallons (136,274.82 litres) of kerosene, at an average density of 0.8 kg/l that is roughly 150,000 litres (39,625.8 gallons). Because turbine oil is consumed in far smaller volumes, the oil-to-fuel ratio remains close to the customary rule of one gallon of oil for every 25 gallons of fuel (3.785 liters of oil for every 94.635 liters of fuel). In 2024 the aviation industry accounts for approximately 8% of global oil consumption, making it the fastest-growing sector in terms of oil demand.
