Question 1

The engine temperature alarm sounds. What is the diagnostic sequence before restarting?

Accepted Answer

Stop engine immediately. Check: 1) Raw water inlet seacock is open; 2) Raw water strainer clear of weed/debris; 3) Exhaust water flowing (check via exhaust when safe); 4) Raw water impeller (inspect if no water flowing); 5) Coolant level in header tank; 6) V-belt intact. Do not restart until the cause is identified. Allow engine to cool fully before opening the coolant system Overheating sequence: the most common cause is raw water flow failure. Seacock closed (crew accidentally knocked it): 30 seconds to check. Raw water strainer blocked: 2 minutes to check and clear. Impeller failed: most common, requires pump cover removal. V-belt broken: 5 seconds to check visually. Coolant level: check header tank. DO NOT open the header tank on a hot engine — pressurised system will cause severe scalding. Once identified and remedied, idle the engine for 10 minutes before return to power to allow even cooling. Continuing with an overheated engine destroys the head gasket.

Question 2

What is the fundamental operating principle of a diesel engine that distinguishes it from a petrol engine?

Accepted Answer

Compression ignition: diesel fuel is ignited by the heat of highly compressed air (compression ratio ~22:1) — no spark plugs are used. Fuel is injected into the compressed air at the moment of ignition Diesel (compression ignition): air is compressed to ~22:1 ratio, reaching ~500-700°C. Diesel fuel (which ignites at ~250°C) is injected directly into this hot compressed air and spontaneously ignites. Petrol engines use ~8:1 compression and require a spark to ignite. The high compression ratio makes diesel engines more thermally efficient (~40% vs ~25% for petrol) and safer (diesel is much less volatile than petrol).

Question 3

Describe the four strokes of a diesel engine cycle in the correct order

Accepted Answer

Induction (air in): piston down, air drawn into cylinder. Compression: piston up, air compressed to high temperature. Power (ignition): fuel injected, combustion drives piston down. Exhaust: piston up, exhaust gases expelled The four-stroke diesel cycle (suck, squeeze, bang, blow): 1) Induction — intake valve open, piston moves down drawing in air only (no fuel). 2) Compression — both valves closed, piston moves up, air compressed to ~22:1. 3) Power — injector fires, combustion, piston driven down. 4) Exhaust — exhaust valve open, piston moves up expelling gases. Two complete crankshaft revolutions per power stroke per cylinder. Multiple cylinders provide smoother, overlapping power strokes.