ABYC Marine Diesel Engine Certification
Practice Exam Questions And Correct
Answers (Verified Answers) Plus
Rationales 2026 Q&A | Instant
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1. What is the primary function of a marine diesel engine’s raw water
pump?
A. To circulate coolant through the closed-loop system
B. To supply seawater for engine cooling
C. To maintain oil pressure in the crankcase
D. To provide air for combustion
Rationale: The raw water pump draws seawater to absorb heat from the
engine’s heat exchanger, preventing overheating.
2. The compression ratio in a diesel engine is typically:
A. 5:1
,B. 8:1
C. 14:1 to 22:1
D. 25:1 to 30:1
Rationale: Diesel engines rely on high compression ratios between 14:1 and
22:1 to ignite fuel through heat of compression.
3. What is the purpose of the fuel return line in a diesel system?
A. To feed fuel injectors directly
B. To vent air from the fuel tank
C. To return excess fuel back to the tank
D. To supply the lift pump
Rationale: Unused fuel and heat are returned to the tank to regulate
temperature and maintain pressure balance.
4. A leaking injector nozzle most likely causes:
A. Hard starting
B. White smoke
C. High oil pressure
D. Overheating
Rationale: Leaking injectors allow unburned fuel into the exhaust, producing
white smoke.
,5. Which ABYC standard applies to diesel fuel systems?
A. ABYC A-4
B. ABYC H-33
C. ABYC E-11
D. ABYC P-1
Rationale: ABYC H-33 covers design, installation, and testing requirements
for diesel fuel systems.
6. What does a high exhaust gas temperature indicate?
A. Excess lubrication
B. Overfueling or restricted air intake
C. Low compression
D. Proper combustion
Rationale: High EGT usually results from excess fuel or inadequate air
causing incomplete combustion.
7. The function of the governor in a diesel engine is to:
A. Control oil pressure
B. Regulate engine speed by adjusting fuel delivery
C. Control water flow
D. Adjust compression ratio
Rationale: Governors automatically adjust the fuel rack to maintain desired
engine speed under load changes.
, 8. The term “bleeding the fuel system” means:
A. Adding fuel additive
B. Cleaning the injectors
C. Removing air from the fuel lines
D. Replacing the lift pump
Rationale: Air in the fuel system prevents injection; bleeding ensures
consistent fuel delivery.
9. Diesel fuel contamination by water can cause:
A. High RPM
B. Blue smoke
C. Microbial growth and injector damage
D. Lower compression
Rationale: Water promotes microbial growth and corrosion, damaging
filters and injectors.
10. What is the most accurate method to check bearing clearance?
A. Feeler gauge
B. Ruler
C. Plastigage
D. Micrometer
Practice Exam Questions And Correct
Answers (Verified Answers) Plus
Rationales 2026 Q&A | Instant
Download Pdf
1. What is the primary function of a marine diesel engine’s raw water
pump?
A. To circulate coolant through the closed-loop system
B. To supply seawater for engine cooling
C. To maintain oil pressure in the crankcase
D. To provide air for combustion
Rationale: The raw water pump draws seawater to absorb heat from the
engine’s heat exchanger, preventing overheating.
2. The compression ratio in a diesel engine is typically:
A. 5:1
,B. 8:1
C. 14:1 to 22:1
D. 25:1 to 30:1
Rationale: Diesel engines rely on high compression ratios between 14:1 and
22:1 to ignite fuel through heat of compression.
3. What is the purpose of the fuel return line in a diesel system?
A. To feed fuel injectors directly
B. To vent air from the fuel tank
C. To return excess fuel back to the tank
D. To supply the lift pump
Rationale: Unused fuel and heat are returned to the tank to regulate
temperature and maintain pressure balance.
4. A leaking injector nozzle most likely causes:
A. Hard starting
B. White smoke
C. High oil pressure
D. Overheating
Rationale: Leaking injectors allow unburned fuel into the exhaust, producing
white smoke.
,5. Which ABYC standard applies to diesel fuel systems?
A. ABYC A-4
B. ABYC H-33
C. ABYC E-11
D. ABYC P-1
Rationale: ABYC H-33 covers design, installation, and testing requirements
for diesel fuel systems.
6. What does a high exhaust gas temperature indicate?
A. Excess lubrication
B. Overfueling or restricted air intake
C. Low compression
D. Proper combustion
Rationale: High EGT usually results from excess fuel or inadequate air
causing incomplete combustion.
7. The function of the governor in a diesel engine is to:
A. Control oil pressure
B. Regulate engine speed by adjusting fuel delivery
C. Control water flow
D. Adjust compression ratio
Rationale: Governors automatically adjust the fuel rack to maintain desired
engine speed under load changes.
, 8. The term “bleeding the fuel system” means:
A. Adding fuel additive
B. Cleaning the injectors
C. Removing air from the fuel lines
D. Replacing the lift pump
Rationale: Air in the fuel system prevents injection; bleeding ensures
consistent fuel delivery.
9. Diesel fuel contamination by water can cause:
A. High RPM
B. Blue smoke
C. Microbial growth and injector damage
D. Lower compression
Rationale: Water promotes microbial growth and corrosion, damaging
filters and injectors.
10. What is the most accurate method to check bearing clearance?
A. Feeler gauge
B. Ruler
C. Plastigage
D. Micrometer
