Question 1

The impeller is changed, the engine restarts, cooling water flows, but the engine produces heavy black exhaust smoke and runs roughly under load. What does black smoke indicate?

Accepted Answer

Black smoke = over-fuelling or incomplete combustion: possibly air filter blocked, engine overloaded, injector issue, or turbocharger problem. Check air filter first; at low throttle it may clear; do not over-rev a rough-running engine Smoke colours: BLACK = incomplete combustion/over-fuelling (check air filter, reduce load, possible injector fault). BLUE = oil burning (worn rings or valve seals). WHITE on warm engine = coolant entering combustion (head gasket). On cold start, some white/grey smoke is normal condensation. Black smoke on a previously clean engine after the fuel system was disturbed may mean an injector has picked up a particle — get it inspected soon.

Question 2

You turn the key. No cranking sound at all — complete silence. What is the most likely fault category and what do you check first?

Accepted Answer

Electrical: check battery voltage (battery monitor or multimeter); check main battery isolator switch is ON and set to the correct bank; check the engine battery is not flat; check the kill/stop control is in the RUN position No crank = electrical fault (unless the decompressor or stop control is engaged). Sequence: 1) Is the battery isolator ON and on the correct bank? 2) Is battery voltage above 12V (10.5V minimum for cranking)? 3) Is the kill/stop control fully in RUN? 4) Is the neutral safety switch in neutral? Do not proceed to fuel diagnosis until you have confirmed electricity is reaching the starter motor.

Question 3

The battery isolator has two banks (1 = House, 2 = Engine, BOTH). The switch is on BOTH. The voltage reads 11.8V. What does this tell you and what do you do?

Accepted Answer

11.8V is borderline for reliable starting — switch to Bank 2 (engine bank only) which may have more charge; reduce all electrical loads; try cranking on the dedicated engine bank A diesel starter motor needs high current (200–500A peak). 11.8V under no load may drop to 9–10V under cranking load on BOTH banks — below the starter's cut-out. Switch to the dedicated engine bank, turn off navigation instruments and VHF to reduce parasitic load, and crank in short bursts (10 seconds max) to avoid overheating the starter. If still no crank, check the starter solenoid wire and starter motor itself.