Oil Systems

[Ref. Pilot’s Handbook of Aeronautical Knowledge, FAA-H-8083-25B Page 7-16, 7-17, 7-19]

(Last Update: 2020 Apr 24 1105Z)

Oil Systems

Importance of engine oil – its major function?

  1. Reducing friction of the engine’s moving parts
    • act as Lubrication liquid
  2. Providing a seal between the cylinder walls and pistons
  3. Removing heat from the cylinders by its circulation (and heat exchange)
    • act as Cooling agent
  4. Cleaning – Carrying away contaminants by its circulation


Oil system may be involved in Turbocharger system – control the waste gate (an adjustable butterfly valve) installed in the exhaust system.

Two types of oil system – Wet-sump or a Dry-sump?

  1. wet-sump system, the oil is located insump that is an integral part of the engine;
  2. dry-sump system, the oil is contained in a separate tank and circulated through the engine by pumps.


Dry-sump systems allow for a greater volume of oil to be supplied to the engine, which means the dry-sump system are more suitable for very large reciprocating engines.


Main Component of Oil System:

  1. 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. For dry-sump system, oil is pumped from the various locations in the engine back to the oil tank by scavenge pumps
  2. oil pressure gauge provides a direct indication of the oil system operation.
  3. oil temperature gauge measures the temperature of oil.
    Notes: Oil temperature gauge gives an indirect and delayed indication of rising engine temperature, but can be used for determining engine temperature if this is the only means available.
  4. cylinder-head temperature gauge (CHT gauge) that indicates a direct and immediate cylinder temperature change.Note: CHT gauge is used to check for the possibility of Detonation.
  5. oil filler cap and dipstick (for measuring the oil quantity) are usually accessible through a panel in the engine cowling


Significance of Oil Temperature

Oil temperature gauge gives an indirect and delayed indication of rising engine temperature

High oil temperature indications may signal a plugged oil line, a low oil quantity, a blocked oil cooler, or a defective temperature gauge;

Low oil temperature indications may signal improper oil viscosity (more common during cold weather operations)

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# Engine System

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