MTC Marine Technician Engine Systems 3 — Questions and Answers
Question 1: On a marine gasoline engine, what symptom typically indicates a failing water pump impeller?
- Excessive oil consumption
- Engine overheating and reduced raw water flow (Correct answer)
- Rough idle and misfiring
- High fuel consumption
Correct answer: Engine overheating and reduced raw water flow
A worn or broken impeller fails to pump sufficient raw water, reducing cooling capacity and causing the engine to overheat.
Question 2: Which tool is used to check crankshaft end play on a marine engine?
- Micrometer
- Dial indicator (Correct answer)
- Feeler gauge
- Bore gauge
Correct answer: Dial indicator
A dial indicator mounted against the crankshaft flange measures axial (end) play when the crank is pushed fore and aft.
Question 3: What does a persistently low oil pressure reading on a marine engine most likely indicate?
- Clogged fuel filter
- Worn main or rod bearings allowing oil to bypass (Correct answer)
- Fouled spark plugs
- Restricted raw water flow
Correct answer: Worn main or rod bearings allowing oil to bypass
Worn crankshaft or rod bearings increase clearance, allowing oil to escape the pressurized circuit faster than the pump can maintain pressure.
Question 4: A technician performing a compression test on a gasoline inboard finds one cylinder reading 90 psi while others read 150 psi. What is the most likely diagnosis?
- Clogged injector on that cylinder
- Worn or damaged piston rings or valves on that cylinder (Correct answer)
- Incorrect ignition timing
- Air in the fuel line
Correct answer: Worn or damaged piston rings or valves on that cylinder
A single low compression reading points to a sealing problem in that cylinder—most commonly worn rings, a burned valve, or a leaking head gasket.
Question 5: What is the correct procedure when checking valve clearance on a marine diesel engine?
- Check with the engine at idle speed
- Check with the cylinder at TDC on the compression stroke and the engine cold or at specified temperature (Correct answer)
- Check only after the engine reaches full operating temperature
- Check with the cylinder at BDC on the power stroke
Correct answer: Check with the cylinder at TDC on the compression stroke and the engine cold or at specified temperature
Valve clearance is measured with the piston at TDC on compression (both valves closed) at the temperature specified by the manufacturer.
Question 6: Which type of marine engine cooling system uses antifreeze and a heat exchanger to transfer heat to raw seawater?
- Direct raw water cooling
- Closed freshwater cooling (heat exchanger cooling) (Correct answer)
- Keel cooling
- Dry exhaust cooling
Correct answer: Closed freshwater cooling (heat exchanger cooling)
A closed freshwater system circulates antifreeze through the engine and transfers heat via a heat exchanger to raw water that is then discharged overboard.
Question 7: What is the primary reason marine engines require more frequent zincs (sacrificial anodes) inspection than engine internal service?
- Zincs degrade at a predictable annual rate
- Galvanic corrosion rate depends on water salinity, temperature, and dissimilar metal contact (Correct answer)
- Zincs are made of consumable fuel additives
- Engine heat accelerates zinc absorption into coolant
Correct answer: Galvanic corrosion rate depends on water salinity, temperature, and dissimilar metal contact
Galvanic corrosion intensity varies with environmental conditions, so anode consumption can be rapid or slow depending on salinity, temperature, and metal pairings present.
MTC Marine Technician Engine Systems 3
On a marine gasoline engine, what symptom typically indicates a failing water pump impeller?