MST Boat Systems & Maintenance 2 — Questions and Answers
Question 1: What is the primary purpose of a marine raw-water strainer?
- Filter debris before it reaches the engine cooling system (Correct answer)
- Separate fresh water from salt water
- Regulate coolant pressure in the closed loop
- Remove oil from bilge water
Correct answer: Filter debris before it reaches the engine cooling system
A raw-water strainer prevents debris, seaweed, and marine growth from clogging the engine's raw-water cooling circuit.
Question 2: Which type of marine battery is best suited for deep-cycle house bank service?
- Cranking (SLI) battery
- AGM deep-cycle battery (Correct answer)
- Standard automotive battery
- Lithium cranking battery
Correct answer: AGM deep-cycle battery
AGM deep-cycle batteries tolerate repeated discharge/recharge cycles and are designed for sustained loads rather than high-burst starting.
Question 3: A technician notices milky-white engine oil on a freshwater-cooled inboard. What is the most likely cause?
- Overfilled oil reservoir
- Water intrusion through a failed heat exchanger or head gasket (Correct answer)
- Use of the wrong oil viscosity
- Contaminated fuel entering the crankcase
Correct answer: Water intrusion through a failed heat exchanger or head gasket
Milky oil indicates coolant or water mixing with the oil, typically caused by a failed heat exchanger or blown head gasket.
Question 4: What does a manifold vacuum test on a marine gasoline engine primarily indicate?
- Fuel pump output pressure
- Overall engine health including valve sealing and timing (Correct answer)
- Ignition coil output voltage
- Thermostat opening temperature
Correct answer: Overall engine health including valve sealing and timing
Manifold vacuum readings reflect combustion efficiency, valve seating, timing accuracy, and cylinder sealing simultaneously.
Question 5: On a stern-drive unit, what component transfers engine torque to the propeller shaft while allowing steering movement?
- Shift actuator rod
- Universal joint (U-joint) assembly (Correct answer)
- Trim tab adjuster
- Driveshaft coupler flange
Correct answer: Universal joint (U-joint) assembly
U-joints in the stern-drive allow the drive unit to pivot for steering while continuously transmitting engine torque to the propeller.
Question 6: Which ABYC standard primarily governs electrical systems on recreational boats?
- ABYC E-11 (Correct answer)
- ABYC H-24
- ABYC P-1
- ABYC S-32
Correct answer: ABYC E-11
ABYC E-11 (AC and DC Electrical Systems on Boats) sets the standards for marine electrical installation and wiring.
Question 7: What is the recommended action when a marine fuel system shows signs of phase-separated ethanol-blended fuel?
- Add a fuel stabilizer and run the engine at high RPM
- Drain and replace the fuel, then clean the tank and fuel system components (Correct answer)
- Mix in additional ethanol to re-blend the fuel
- Add isopropyl alcohol to absorb the water layer
Correct answer: Drain and replace the fuel, then clean the tank and fuel system components
Phase-separated fuel must be discarded because the water-ethanol layer can cause corrosion and lean running; the tank should be cleaned before refilling.
MST Boat Systems & Maintenance 2
What is the primary purpose of a marine raw-water strainer?