Why won't my marine diesel engine start?
My yacht's diesel wouldn't start after standing for several weeks. The panel lights come on, but I'm not sure whether it's turning over fast enough. What should I check before calling an engineer?
Answer
First check whether the starter turns the engine briskly, slowly or not at all: this separates an electrical starting fault from a fuel or combustion problem. Check neutral, the battery connections and the fuel shut-off valve first, as these simple faults can mimic an expensive failure.
1. Slow cranking or no cranking
Put the gearbox firmly in neutral and check that the battery isolator is on. Working panel lights or an illuminated glow-plug switch do not prove the battery can power the starter. Lamps draw very little current.
- Measure at the battery posts. A rested, charged conventional 12V lead-acid battery usually reads about 12.6 to 12.8V. Watch the meter while someone operates the starter. A drop below roughly 9.6 to 10V is suspicious, though temperature and the engine specification affect the reading.
- Inspect both sides of the circuit. Check the positive cable to the starter and the negative cable where it bolts to the engine block. Loose clamps, green corrosion and a rusty engine earth connection can prevent starting even with a charged battery.
- Check the control supply. Use the wiring diagram to locate the engine fuse, resettable breaker and starter relay. Their positions vary by engine and installation. On Volvo Penta MD2030 installations, inspect the engine wiring box and its connections.
Isolate the battery before removing or cleaning starter cables, and keep tools clear of exposed positive terminals. Tighten connections to the component manufacturer's specification. There is no universal terminal torque.
Rapid clicking commonly points to low voltage or a poor connection. One solid click without rotation can indicate a faulty solenoid or starter, or a mechanically locked engine. Silence can point to the neutral switch, start switch, relay or control wiring. These are clues, not proof.
2. Normal cranking: fuel checks
Start at the tank and work towards the engine. Confirm there is fuel with a reliable level check, particularly if you doubt the gauge, and make sure the supply valve is open. Check that a manual stop cable has returned fully or that the stop solenoid operates correctly.
- Inspect the primary filter/water separator. Look for water, sludge or a blocked element. Dark slime suggests tank contamination that needs more than a filter change.
- Check the engine-mounted filter. Replace an overdue or suspect element with the correct part and renew its seals.
- Look for air leaks. Loose unions, damaged filter seals and cracked suction hoses can admit air without any visible diesel leak.