MTC Preventive Maintenance Procedures 3 — Questions and Answers
Question 1: When performing PM on a marine battery bank, what voltage reading on a fully charged 12V flooded lead-acid battery indicates acceptable state of charge?
- 11.5–11.8 V
- 12.6–12.8 V (Correct answer)
- 13.5–14.0 V
- 10.8–11.2 V
Correct answer: 12.6–12.8 V
A fully charged 12V flooded lead-acid battery at rest should read approximately 12.6–12.8 V; lower readings suggest partial or full discharge.
Question 2: A PM checklist calls for inspecting the marine AC generator's drive belt. Which finding requires immediate replacement?
- Belt has been in service for 12 months
- Belt shows surface glazing, cracking, or fraying (Correct answer)
- Belt deflects slightly when pressed
- Belt is the original equipment manufacturer part
Correct answer: Belt shows surface glazing, cracking, or fraying
Glazing, cracking, or fraying indicates belt degradation that can lead to slippage or sudden failure, interrupting battery charging and cooling.
Question 3: During a PM inspection of a marine vessel's through-hull fittings, what condition should prompt immediate haul-out and repair?
- Minor surface discoloration from algae
- Fitting is the original bronze material
- Dezincification (pinkish, porous appearance) or visible cracking of the fitting (Correct answer)
- Fitting is located below the waterline
Correct answer: Dezincification (pinkish, porous appearance) or visible cracking of the fitting
Dezincification weakens brass/bronze fittings significantly, and a failed through-hull below the waterline can sink the vessel rapidly.
Question 4: What is the correct method to test a marine bilge pump's automatic float switch during PM?
- Fill the bilge completely with water and wait
- Manually lift the float switch while observing pump activation (Correct answer)
- Disconnect the pump and test with a multimeter only
- Run the vessel at full throttle for 30 minutes
Correct answer: Manually lift the float switch while observing pump activation
Manually lifting the float switch simulates rising water and confirms the pump activates without having to flood the bilge.
Question 5: When topping off a marine diesel day tank as part of a PM procedure, what is the correct reason to leave an air gap at the top of the tank?
- To allow fuel to expand with temperature changes and prevent overflow (Correct answer)
- To reduce the weight of fuel carried
- To improve fuel atomization in injectors
- To allow air to mix with fuel for better combustion
Correct answer: To allow fuel to expand with temperature changes and prevent overflow
Diesel fuel expands as temperature rises, and leaving a small air gap prevents overflow through the vent or filler cap.
Question 6: A PM schedule requires inspecting marine engine mounts. Which symptom most strongly suggests engine mounts need replacement?
- Engine runs at normal RPM
- Excessive vibration transmitted to the hull or visible rubber deterioration (Correct answer)
- Engine starts easily on the first crank
- Oil pressure within normal range
Correct answer: Excessive vibration transmitted to the hull or visible rubber deterioration
Deteriorated or collapsed engine mounts transfer vibration directly to the hull structure and can cause misalignment of the propeller shaft.
Question 7: What is the purpose of winterizing a freshwater cooling system with propylene glycol antifreeze rather than ethylene glycol?
- Propylene glycol provides better freeze protection below -60°F
- Propylene glycol is less toxic if it enters the bilge or waterways (Correct answer)
- Propylene glycol is cheaper and easier to find
- Propylene glycol improves corrosion protection in aluminum engines
Correct answer: Propylene glycol is less toxic if it enters the bilge or waterways
Propylene glycol is generally recognized as safe (GRAS) and is environmentally preferable for marine use because ethylene glycol is toxic to aquatic life.
MTC Preventive Maintenance Procedures 3
When performing PM on a marine battery bank, what voltage reading on a fully charged 12V flooded lead-acid battery indicates acceptable state of charge?