Lubrication Systems

Question 1

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

Answer 1

The piston rings are worn or broken.

Question 2

What are the functions of lubricating oil in reciprocating engines?

Answer 2

To reduce friction between moving parts and remove heat.

Question 3

Name two important characteristics of aircraft oil.

Answer 3

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

Question 4

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

Answer 4

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

Question 5

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 5

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

Question 6

Why do aircraft reciprocating engines use a relatively high viscosity oil?

Answer 6

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

Question 7

Name some oil contaminants.

Answer 7

Metal particles, dirt, carbon, moisture, and acids.

Question 8

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

Answer 8

A low or inadequate supply of oil.

Question 9

In ashless dispersant oils, what function does the dispersant perform?

Answer 9

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 10

Why do oil reservoirs have expansion space?

Answer 10

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

Question 11

What could cause oil foaming?

Answer 11

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

Question 12

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

Answer 12

An oil pressure relief valve.

Question 13

What function does an oil cooler bypass valve perform?

Answer 13

It directs the oil either through the cooler or around it to maintain proper operational temperatures.

Question 14

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

Answer 14

A high oil temperature.

Question 15

Where is the oil temperature bulb usually located?

Answer 15

At the engine oil inlet.

Question 16

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

Answer 16

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

Question 17

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

Answer 17

Follow engine manufacturer’s maintenance instruction.

Question 18

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

Answer 18

At the turbine bearing.

Question 19

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

Answer 19

Synthetic oil.

Question 20

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

Answer 20

At the oil pressure system (main filter), scavenge system, and at or just before the oil jet (last chance).

Question 21

Name two types of turbine engine oil coolers.

Answer 21

Air cooled and fuel cooled.

Question 22

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

Answer 22

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