Coast Guard QMED Oiler Examination

Coast Guard QMED Oiler Examination Practice Questions And Correct Answers (Verified Answers) Plus Rationales 2026 Q&A | Instant Download Pdf

1. The main purpose of the jacket water system in a diesel engine is to:

a) Lubricate the pistons

b) Cool the engine c) Heat the fuel

d) Vent exhaust gases

Rationale: The jacket water system circulates water around the cylinders

to absorb heat and maintain proper engine temperature.

• What is the normal operating pressure for a typical shipboard

lubricating oil system?

• 50–75 psi
• 30–50 psi c) 60–90 psi
• 100–120 psi 1 / 4

Rationale: Most marine lubricating oil systems operate within 60–90 psi to

ensure proper bearing lubrication.

• Which type of pump is typically used for fuel oil transfer aboard a

ship?

a) Gear pump b) Centrifugal pump

c) Piston pump

d) Screw pump

Rationale: Centrifugal pumps are preferred for fuel oil transfer because of

their continuous flow and ability to handle large volumes.

4. The primary function of a marine boiler economizer is to:

a) Increase steam pressure

b) Heat the combustion air c) Recover heat from flue gases

d) Feed water to the boiler

Rationale: Economizers capture residual heat from flue gases to preheat

feed water, improving overall boiler efficiency.

• Which of the following is a common symptom of low lube oil pressure

in a diesel engine?

a) Smoke from exhaust

b) High engine temperature c) Bearing noise or knocking

d) Excessive vibration

Rationale: Low oil pressure can cause insufficient lubrication of bearings,

resulting in knocking or unusual noise. 2 / 4

6. When starting a diesel engine, the turning gear is used to:

a) Burn off carbon deposits

b) Cool the cylinder c) Rotate the engine slowly

d) Circulate lubricating oil

Rationale: The turning gear slowly rotates the engine for maintenance or

inspection before starting.

• Which type of heat exchanger is commonly used for cooling lube oil on

a ship?

a) Plate-type b) Shell-and-tube

c) Air-cooled finned

d) Spiral

Rationale: Shell-and-tube heat exchangers are standard for lube oil cooling

due to efficiency and robustness.

8. A bilge pump on a ship is primarily used to:

a) Pump fuel

b) Cool machinery c) Remove water from the bilge

d) Transfer lubricating oil

Rationale: Bilge pumps are designed to remove accumulated water from

the bilge spaces of a ship.

9. The main purpose of a centrifugal purifier is to:

a) Increase fuel flow 3 / 4

b) Heat lube oil c) Separate water and sediment from oil

d) Pressurize the fuel system

Rationale: Centrifugal purifiers remove contaminants and water from fuel

or lube oil, ensuring clean oil supply.

• What is the purpose of a relief valve in a lubricating oil system?

a) Filter the oil

b) Increase flow c) Prevent overpressure

d) Heat the oil

Rationale: Relief valves protect the system from excessive pressure by

opening when pressure exceeds a set limit.

• Which type of bearing is most commonly used in marine diesel

main engines?

a) Roller bearing

b) Ball bearing c) Journal bearing

d) Needle bearing

Rationale: Journal bearings support rotating shafts under heavy load,

common in large marine diesel engines.

• The normal color of exhaust smoke indicating proper

combustion in a diesel engine is:

a) Blue

b) Black c) White

d) Gray

• / 4