CLS Lubrication Systems & Maintenance 3 — Questions and Answers
Question 1: When inspecting a circulating oil lubrication system, a technician notices the oil level in the reservoir is dropping faster than expected. What is the MOST likely cause?
- Oil viscosity has increased
- External leaks or excessive foaming causing overflow (Correct answer)
- The oil has degraded and become denser
- The system is operating at lower than normal temperature
Correct answer: External leaks or excessive foaming causing overflow
Rapid reservoir level drops typically indicate external leaks at seals or fittings, or severe foaming causing oil to overflow from the reservoir breather.
Question 2: What is the recommended approach when switching from a mineral-based lubricant to a synthetic in a circulating system?
- Add the synthetic directly on top of the mineral oil
- Drain, flush the system, and refill with synthetic (Correct answer)
- Mix equal parts synthetic and mineral to transition gradually
- Increase the operating temperature first to improve compatibility
Correct answer: Drain, flush the system, and refill with synthetic
A proper drain and flush removes residual mineral oil and incompatible additives before introducing synthetic lubricant to prevent contamination and additive interaction.
Question 3: What is the purpose of a magnetic drain plug in a gearbox?
- To monitor oil temperature at the drain point
- To capture ferrous wear particles and prevent recirculation (Correct answer)
- To increase oil drain speed
- To prevent oil from draining when not servicing
Correct answer: To capture ferrous wear particles and prevent recirculation
Magnetic drain plugs attract and hold ferrous metal wear particles, preventing them from recirculating through the gearbox and causing additional wear.
Question 4: In a grease lubrication system using progressive divider valves, how is a blocked outlet typically detected?
- A drop in system pressure at the pump
- A pressure indicator or cycle switch on the divider valve activates (Correct answer)
- The grease changes color at the blocked point
- System automatically increases pump speed
Correct answer: A pressure indicator or cycle switch on the divider valve activates
A blocked outlet causes pressure to build in the progressive valve, triggering a built-in pressure indicator (pin indicator or cycle switch) that signals the fault.
Question 5: Which parameter BEST indicates the remaining useful life of a circulating oil system lubricant?
- Oil color alone
- Remaining base number (BN) or acid number (AN) trend (Correct answer)
- Reservoir oil level
- Oil pump discharge pressure
Correct answer: Remaining base number (BN) or acid number (AN) trend
Tracking the base number (BN) depletion or acid number (AN) rise through oil analysis indicates how much additive reserve remains and predicts when the oil must be changed.
Question 6: What is the main function of a vented (breather) cap on a lubricant reservoir?
- To add make-up oil without opening the reservoir
- To allow air exchange while filtering out contaminants (Correct answer)
- To pressurize the reservoir for pump priming
- To measure the oil level visually
Correct answer: To allow air exchange while filtering out contaminants
A breather cap allows air to flow in and out as the oil level changes while filtering particulate and moisture contamination from incoming air.
Question 7: A grease-lubricated bearing shows signs of overheating. After verifying cooling is adequate, what lubrication-related cause should be investigated FIRST?
- Grease viscosity is too low for the speed
- Bearing housing is over-packed with grease (Correct answer)
- The grease has excessive water content
- Grease was applied too long ago
Correct answer: Bearing housing is over-packed with grease
Over-packing a bearing housing with grease creates excessive churning resistance, generating heat; this is one of the most common causes of grease-lubricated bearing overheating.
CLS Lubrication Systems & Maintenance 3
When inspecting a circulating oil lubrication system, a technician notices the oil level in the reservoir is dropping faster than expected.
What is the MOST likely cause?