Engine Lubrication Systems

Question 1

What is straight mineral oil?

Answer 1

It is the lubricating oil as obtained by frictional distillation of crude oil. It does not have an additives

Question 2

What is ashless dispersant (AD) oil?

Answer 2

A mineral lubricating oil containing additives that disperse the contaminants throughout the oil so they will not clump and clog oil passages. There are no ash-forming additives in AD oil

Question 3

What is synthetic oil?

Answer 3

A lubricating oil is made by chemically changing the nature of an oil base to give it the needed characteristics. Synthetic oil is the primary oil for turbine engines

Question 4

Is automotive oil suitable for use in aircraft engines?

Answer 4

No, automotive and aviation oils are formulated for entirely different operating conditions

Question 5

What is meant by a multiviscosity oil?

Answer 5

It is a lubricating oil with a viscosity index improver that increases the viscosity of the oil when it is hot and decreases the viscosity when it is cold

Question 6

Where can you find the grade of engine oil specified for a particular aircraft?

Answer 6

In the airplane flight manual or the pilot’s operating handbook for the aircraft

Question 7

What are the six functions of the oil in an aircraft engine?`

Answer 7

1. Reduces friction
2. Seals and cushions
3. Removes heat
4. Cleans inside the engine
5. Protects against corrosion
6. Performs hydraulic action

Question 8

How is oil pressure regulated in an aircraft engine?

Answer 8

A pressure-relief valve senses the desired pressure and sends excess oil back into the engine sump

Question 9

What is the purpose of an air-oil separator, or deaerator, in a turbine engine oil tank?

Answer 9

The oil picks up a quantity of air and it is swirled as it enters the deaerator. The swirling action releases the air from the oil, and the air is used to pressurize the oil tank

Question 10

What is the purpose of the restricted orifice in the line between the oil pressure gauge and the engine?

Answer 10

The restricted fitting helps dampen any pulsations in the oil pressure caused by the pump

Question 11

What is a hot-tank lubrication system for a turbojet engine?

Answer 11

A lubrication system in which the oil cooler is in the pressure subsystem and the scavenged oil is not cooled before it is returned to the tank

Question 12

What is a cold-tank lubrication system for a turbojet engine?

Answer 12

A lubrication system in which the oil cooler is in the pressure subsystem and the scavenged oil is cooled before it is returned to the tank

Question 13

What could be a possible indication if the oil cooler passage becomes obstructed?

Answer 13

A high oil temperature.

Question 14

Where is the oil temperature build usually located?

Answer 14

At the engine oil inlet.

Question 15

What does the presence of metal particles in an engine oil filter indicate?

Answer 15

Depending on the type and size of the metal particles, this usually indicates abnormal wear and possible engine internal failure.

Question 16

What should be done if metal particles are found in an engine oil filter?

Answer 16

Follow engine manufacturer’s maintenance instructions.

Question 17

Where is the most critical point of lubrication in a gas turbine engine?

Answer 17

At the turbine bearing.

Question 18

What type of oil is used in a turbine engine oil system?

Answer 18

Synthetic oil.

Question 19

Where are oil screens or filters most likely located in a turbine engine oil system?

Answer 19

1. At the oil pressure system (main filter)
2. Scavenge system
3. At or just before the oil jet (last chance)

Question 20

Name two types of turbine engine oil coolers.

Answer 20

1. Air cooled
2. Fuel cooled.

Question 21

What could happen to an oil that is too low in viscosity at normal engine operating temperatures?

Answer 21

It may become so thin that the oil film between moving parts is easily broken resulting in premature wear.

Question 22

A reciprocating engines is found to have excessive oil consumption without evidence of any oil leaks. What is the likely cause?

Answer 22

The piston rings are worn or broken.

Question 23

What are the functions of lubricating oil in reciprocating engines?

Answer 23

To reduce friction between moving parts and remove heat.

Question 24

Name two important characteristics of aircraft engine oil.

Answer 24

The oil must be light enough to circulate freely yet heavy enough to provide oil film at the engine operating temperatures.

Question 25

What are some of the factors that must be considered by an engine manufacturer in determining the proper grade of oil for a particular engine?

Answer 25

The operating load and temperature as well as the rotational speed.

Question 26

Why do aircraft reciprocating engines use relatively high viscosity oil?

Answer 26

Because they usually have large operating clearances, and operate at high temperatures and pressures.

Question 27

Name some oil contaminants.

Answer 27

1. Metal particles
2. dirt
3. carbon
4. moisture
5. acids

Question 28

What is a possible indication of low oil pressure together with high oil temperature?

Answer 28

A low or inadequate oil supply.

Question 29

In ashless dispersant (AD) oils, what function does the dispersant perform?

Answer 29

causes contaminants to disperse throughout the oil so it doesn’t clump up and block oil passages
The dispersant causes sludge-forming materials to repel each other and remain in suspension until they can be trapped by the oil filter or drained. This keeps the oil passages and ring grooves free of harmful deposits, and the inside of the engine clean.

Question 30

Why do oil reservoirs have expansion space?

Answer 30

To provide for oil foaming, thermal expansion, and air in the return oil.

Question 31

What could cause oil foaming?

Answer 31

Diluted oil, contaminated oil, and the oil level being too high.

Question 32

What controls oil pressure in a gear-type oil pressure pump?

Answer 32

An oil pressure relief valve.

Question 33

What function does an oil cooler bypass valve perform?

Answer 33

It directs the oil either through the cooler or around it in order to maintain proper operating oil temperatures.