Lubrication systems consist of either a wet-sump or Dry-sump system
The difference between the two systems can be remembered as if the engine were off
Wet sump systems maintain oil in reservoirs integral to the engine while dry sumps do not, leaving the sump "dry"
Wet-Sump:
Oil is carried in a sump, which is an integral part of the engine [Figure 2]
The main component is the 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
In some engines, additional lubrication is supplied by the rotating crankshaft, which splashes oil onto portions of the engine
Pilot Handbook of Aeronautical Knowledge, Wet-Sump Oil System
Dry-Sump:
Oil is contained in a separate tank, and circulated through the engine by pumps
These tanks are always larger than the oil it is meant to contain to compensate for thermal expansion
An oil pump also supplies oil pressure in a dry-sump system, but the source of the oil is located external to the engine in a separate oil tank
After oil is routed through the engine, it is pumped from the various locations in the engine back to the oil tank by scavenge pumps
Dry-sump systems allow for a greater volume of oil to be supplied to the engine, which makes them more suitable for very large reciprocating engines
Most jet engines will consist of a dry sump design
When checking the oil level on an dry-sump engine that has been sitting idle, readings may be inaccurate unless rotated (or "burped")
Refer to your POH
The oil filler cap/dipstick used to measure oil quantity is usually accessible through a panel in the engine cowling [Figure 2]
If the quantity does not meet the manufacturer's recommended operating levels, oil should be added
The type of oil required may vary on numerous atmospheric and operation conditions, as stipulated by the aircraft operations manual [Figure 1]
The AFM/POH or placards near the access panel provide information about the correct oil type and weight, as well as the minimum and maximum oil quantity
Pilot Handbook of Aeronautical Knowledge, Checking Engine Oil Level
Pilot Handbook of Aeronautical Knowledge, Checking Engine Oil Level
The loss of engine oil pressure would lead to engine vibrations, RPM would decrease, and the engine would eventually seize
Viscosity:
the ability of a liquid to resist flow
Heat Management:
A critical purpose of engine oil is to help manage cooling
This occurs by cool oil moving through warm areas, picking up the heat, and dissipating it through a radiator
Oil System Gauges:
Pilot Handbook of Aeronautical Knowledge, Oil Temperature and Pressure Gauge
Oil Pressure Gauge:
The oil pressure gauge provides a direct indication of the oil system operation [Figure 3]
It ensures the pressure in pounds per square inch (psi) of the oil supplied to the engine
Green indicates the normal operating range, while red indicates the minimum and maximum pressures
There should be an indication of oil pressure during engine start
Refer to the AFM/POH for manufacturer limitations
Oil Temperature Gauge:
The oil temperature gauge measures the temperature of oil [Figure 3]
It is usually measured after passing through the oil cooler
A green area shows the normal operating range and the red line indicates the maximum allowable temperature
Unlike oil pressure, changes in oil temperature occur more slowly
This is particularly noticeable after starting a cold engine, when it may take several minutes or longer for the gauge to show any increase in oil temperature
Check oil temperature periodically during flight especially when operating in high or low ambient air temperature
High oil temperature indications may signal:
Plugged oil line or cooler
low oil quantity (possible engine failure)
Defective temperature gauge
High oil temperatures can lead to metal on metal contact as viscosity decreases
Low oil temperature indications may signal improper oil viscosity during cold weather operations
Oil/Lubrication Malfunctions/Emergencies:
Oil consumption depends primarily upon the efficiency of the seals
Oil can be lost through internal leakage, and, in some engines, by malfunctioning of the pressurizing or venting system
Increases in oil temperature are not always associated with a drop in oil pressure, nor a rise in CHTs
Low Oil Pressure:
Low oil pressure can be caused by an oil leak which leads to lack of oil in the system, or an ineffective oil pump
These emergencies can be particularly detrimental when flying an aircraft utilizing a constant-speed propeller
Low Oil Pressure Primary Indications:
Oil pressure will indicate low
Low Oil Pressure Secondary Indications:
Rising Cylinder Head Temperatures (CHT)
Oil temperature may rise (if the pressure drops rapidly then it is less likely you will have a corresponding temperature indication
Rough engine indications
Low Oil Temperature:
Primary Indications:
Oil temperature will indicate low
Secondary Indications:
High Oil Temperature:
High Oil Temperature Primary Indications:
Oil temperature will indicate high
High Oil Temperature Secondary Indications:
Other temperatures will indicate high
Possible smoke
Low oil pressure
High RPM
High Oil Temperature Considerations:
Open cowl flaps, if equipped
Oil Leaks:
Oil on windscreen may come from engine or propeller
Oil System Inspections:
Inspecting the oil system is not a routine check, but rather a detailed review of aircraft engine health
Oil Inspection:
Pilots should inspect the oil as part of the pre-flight checklist
Inspecting the oil is critical in determining the quantity and condition of oil
Oil should never go below the Pilot Operating Handbook specified minimum quanty
The color of the oil is a reflection of oil age and engine health
New, clean oil should be light in color
Dark oil is generally the result of contaminates and oxidation after many hours of operation
Too dark is a judgement call based on the amount of hours of use
Dark oil may be due to bad piston seals
Larger oil sumps tend to absorb contaminents better as they hold more in suspension
Smaller sumps should therefore be changed/drained more often
Oil Filter Inspection:
It is never required, but pilots who own their airplane may elect to inspect the oil filter for tell-tale signs of wear
Oil filters are designed to bypass, if clogged, but are only meant to last for the life of the oil
Oil filters should be changed with every oil change
Changing an oil filter often also allows for consistent engine health trend analysis
Lubrication System Airman Certification Standards:
Oil systems reduce friction on moving parts, create better seals, reduce and remove heat, carry away contaminants and in some cases, run other systems
Oil can be sent off for analysis which checks small particles not caught by filter, but a filter will hide big issues
Many systems have pressurized sumps and a pressurized oil tank to ensure a constant head pressure to the lubrication pump to prevent pup cavitation at high altitudes
Changing oil is permitted as preventative maintenance and provides an indication of engine health
Oil consumption is relatively low in a gas turbine engine compared to a piston-type engine
