Lubrication And Cooling 2

Question 1

Engine oil system vs cooling system

Answer 1

Engine oil cools and lubricates and cleans and seals
Cooling system just cools

Question 2

Lubrication purpose

Answer 2

Reduce friction between metal moving parts (reduce heat and damage)
Changes mechanical friction into shear stress in oil film
Reduces heat means less metal expansion
Cushioning against mechanical shock

Question 3

Dipstick colour meanings

Answer 3

Light brown : new oil no change needed
Amber : good no change needed
Dark brown : probably old replace oil and filter
Black : sludge probable contaminating change oil and filter
Milky : check head gasket probable water contamination

Question 4

Difference between aviation automotive oil

Answer 4

Higher rpm and operating loads on bearing and gears in aviation
Higher temp of air cooled engines in aviation

Question 5

Burning oil signs

Answer 5

Blue tinged smoke From exhaust

Question 6

Wet vs dry sump

Answer 6

Wet:
Sump doubles as storage tank for oil
Not suitable for radial or aerobatic
Used in DA 40

Dry sump:
Oil stored in seperate tank
Scavenge pumps feed oil from sumo to oil tank
Allows for continuous lubrication even in extreme attitudes (good for aerobatic ac)

Question 7

Filters and screens

Answer 7

Remove contamination (bits of metal dirt carbon deposits)
Inspected and replaced on maintenance schedule
Filter had bypass valve in case of clogging (dirty oil better than no oil)

Question 8

Oil cooler

Answer 8

Thermal valve allows bypass if oil is cool enough (cold oil higher pressure)
Pressure bypass in case of blockage
Maximises surface area

Question 9

Oil gauges

Answer 9

Pressure ( measured between pump and engine)
Temp (measured after cooler)
Temp increases equal pressure decrease

Question 10

Oil types

Answer 10

Mineral oil
Used in piston engines
From crude oil
Non uniform

Synthetic oil
Used in cars
Polymerisation of hydrocarbon molecules
Invented for high temp gas turbine engine applications

Question 11

Straight mineral oil

Answer 11

Forms gummy residue and carbon deposits
Prone to oxidation at high temps
For engine running in

Question 12

Detergent oils

Answer 12

Development of straight oils
Contain additives to reduce oxidation and get rid of carbon deposits
Can form metallic ash compounds and clog system
Not used in aero engines

Question 13

Ashless dispersant oil

Answer 13

Reduced oxidation and sludge compared to straight mineral
Don’t form ash deposits
Typically used In Aviation

Question 14

Oil properties

Answer 14

Viscosity (thickness of oil too viscous won’t move or pour not viscous enough won’t seal or lubricate effectively)
Pour point (lowest temp at which oil pours satisfactorily)
Flash point (lowest temp oil starts giving off ignitable vapour’s)

Question 15

Oil grades

Answer 15

Society of automotive engineers (SAE)
Kinematic viscosity (takes into account density of fluid to better measure energy required to move it)
SI unit (m2/s) or CGS 1 stoke = 1cm2/s = .0001m2/s
1 stoke = 100 centistokes

Question 16

Single grade oil

Answer 16

Viscosity determined at 100°c (operating temp for auto engine not aero )
Higher viscosity = higher number = better performance
Aviation uses commercial index
Can have a w for winter temps (oil is expected to maintain viscosity)

Question 17

Viscosity index

Answer 17

Set up by ASTM
originally 0-100
Oils have surpassed 100 rating

Question 18

Multi grade oil

Answer 18

Meets more than one SAE viscosity classification(performs well in cold and warm)
Suitable for use over wider range of temps
Polymer additives called viscosity index improvers reduce difference between high temp and low temp viscosity
W tested at 0° f or -17.8° c
Ex 10w-30
Number before w lower is better after higher is better

Question 19

Oil selection basic rules of thumb

Answer 19

Light = less dense
1. Lower temp lighter oil and vice versa
2. Higher load (more pressure) heavier oil and vice versa
3. Faster movement lighter oil and vice versa

Question 20

Operational aspects

Answer 20

Oil level gradually reduces due to burning leaks or lost as mist/spray
Low level results in low oil pressure and overheating
High oil level means excess is forced out

Question 21

Starting engine

Answer 21

Oil pressure should rise within 15s of starting (60 in cold temps)

Question 22

Malfunctioning oil pressure causes

Answer 22

Low oil pressure:
Insufficient oil due to
Leak
Pump failure
Pressure relief valve stuck open

High oil pressure:
Can cause failure of the whole system
Pressure relief valve not working

Faulty oil pressure gauge (if temp remains consistent)

Question 23

Malfunctioning oil temp

Answer 23

High temp
Not enough oil
Prolonged operation with high CHT (climb high lower low speed)

Question 24

Engine seizure

Answer 24

High temps expanding parts engine stops moving

Question 25

Hydraulic shock

Answer 25

Too much oil pressure distributed to weakest points causing damage

Question 26

Cooling system

Answer 26

Cooling circulating oil
Expelling hot exhaust
Air cooling system circulating cool air around engine

Excessive heat causes
Incorrect burning (detonation pre ignition)
Weakens and reduces life of engine parts
Impairs adequate lubrication

Question 27

Cooling fins

Answer 27

Increase surface air that cool air hits around cylinders

Question 28

Disadvantages of air cooling

Answer 28

Least effect at high power low speed (when you need it most)
Most effective at high airspeed low power (almost too effective)

Question 29

Baffles

Answer 29

Air cooling gathers cool air from behind prop and evenly spreads it around cylinders

Question 30

Cowl flaps

Answer 30

Adjustable and allow for more air flow around the engine