Faults & Troubleshooting (Marine Engines)
Contents
- 1. Rapid Troubleshooting Method (Do This First)
- 2. Engine Fails to Start / Won’t Turn / Won’t Fire
- 3. Exhaust Smoke & Exhaust Abnormalities
- 4. Low Power / Poor Acceleration / High Fuel Rate
- 5. Loss of Lube Oil Pressure / Oil System Faults
- 6. Engine Overheating / High Temps (FW, LO, Exhaust)
- 7. Excessive Vibration / Fluctuating RPM / Hunting
- 8. Crankcase Explosions & Hot Spots (High Severity)
- 9. Quick Reference: Symptom → Likely System
- 10. Glossary (Marine Engineer Edition)
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1. Rapid Troubleshooting Method
1.1 Safety triage (30 seconds)
If ANY of these apply, slow/stop immediately and switch to damage-control mode:
- Lube oil pressure collapse
- Crankcase mist / oil mist detector alarm
- Crankcase doors warm / bearing temp rising
- Overspeed / governor runaway
- Coolant loss with rapid temperature rise
- Unusual banging/knock + vibration spike
- Fuel leak spray / hot surfaces
1.2 The “4 questions” that save hours
- What changed right before the fault? (maintenance, fuel change, weather, load, filter change)
- Is it sudden or gradual? (sudden = control/supply failure; gradual = fouling/wear)
- Is it one cylinder or all cylinders? (one cyl = injector/valve/compression; all = fuel/air/timing/system)
- Does it follow load? (only at high load = air/turbo/exhaust restriction; only at low load = combustion stability/governor/starting)
1.3 Minimal instrumentation you should trust
- Start air manifold pressure (bar)
- LO pressure (bar) + LO temp
- JW (fresh water) temp in/out
- Exhaust temps (per cyl if available)
- Scavenge air pressure / receiver pressure (2-stroke)
- Fuel rail pressure / supply pressure (EC engines)
- Crankcase pressure / OMD
- Battery voltage under load (electric start)
2. Engine Fails to Start / Won’t Turn / Won’t Fire
2.1 Separate the symptom (critical)
A) Starter engaged but engine won’t crank (no turn)
B) Engine cranks slowly (low speed)
C) Engine cranks normally but won’t fire (no combustion)
D) Engine fires briefly then stalls
E) Air-start engine: air admitted but no rotation / weak rotation
2.2 Cranks slowly (electric start) — Battery/Starter/Drag
Quick decision table
| Symptom | Fast Check | Likely Cause | Confirmation | Corrective Action |
|---|---|---|---|---|
| Starter sluggish, lights dim | Measure battery voltage under load | Low battery capacity / sulfation | Voltage collapses during crank | Swap to other bank; charge/replace battery |
| Hot battery terminals | Touch-test (careful) + inspect | Loose/dirty terminals | Heat at joint + oxidation | Clean, tighten, re-terminate |
| Starter clicks only | Listen + relay test | Solenoid/relay issue | Solenoid chatters | Replace solenoid/relay, check wiring |
| Starter spins but no crank | Observe pinion engagement | Pinion not engaging ring gear | Freewheel sound | Starter drive repair, ring gear inspection |
| Cranks stiff after overhaul | Hand-turn on turning gear | Tight engine / cold oil | High turning resistance | Warm engine, correct oil grade, run-in procedure |
Notes
- Diesel needs higher crank speed than petrol because ignition depends on compression heat.
- Wrong viscosity oil in cold conditions can “simulate” a mechanical fault.
2.3 Air supply & exhaust restriction (all engine types)
| Check | Why it matters | What “bad” looks like | Fix |
|---|---|---|---|
| Air filter / intake | No air = no oxygen = no start | Filter blocked, intake flap shut | Clean/replace element, open flaps |
| Engine room ventilation | Fans/flaps affect combustion stability | Vacuum effect / smoky start | Restore airflow, open louvers |
| Exhaust outlet | Exhaust back-pressure kills scavenging | Flap valve stuck, obstruction | Clear obstruction, repair flap |
| Silencer baffle | Can collapse & block | Sudden no-start after bang | Inspect/repair silencer |
2.4 Compression & timing
Low compression across engine (multiple cylinders)
Likely causes:
- Incorrect valve timing (post-maintenance)
- Incorrect tappet clearance (valves riding)
- Worn liners / rings (blow-by)
- Cold engine (heat loss)
- Head gasket leak (bubbles/header tank)
Confirmation checks
- Compression test / peak pressure indicator (where applicable)
- Blow-by observation (2-stroke scavenge drains, crankcase breathers)
- Tappet clearance check at correct crank angle
- Timing marks alignment (gear train)
2.5 Fuel delivery (common, simple, often missed)
| Fuel fault | What you see | Confirmation | Fix |
|---|---|---|---|
| Tank empty / suction leak | No pressure, air in lines | Sight glass/return flow poor | Refill, repair leak, bleed |
| Shut valve closed | No delivery at filter | Valve position + suction vacuum | Open/lock valve, tag-out rules |
| Lift pump failed | Low supply pressure | Manual prime won’t build | Overhaul/replace lift pump |
| Filter choked | Supply pressure drop, stalls | Differential pressure if fitted | Change elements, clean system |
| Air in system | Starts then dies / misfires | Bubbles at bleed points | Bleed systematically, fix leak |
| Injection timing wrong | Smoky start, rough running | Timing check vs marks | Retime pump / ECU calibration |
2.6 Two-stroke specific “won’t start” checks
- Start air distributor / pilot valves not sequencing
- Starting air valves leaking (air blowback into manifold)
- Turning gear interlock engaged (no start permission)
- Scavenge drains flooded (liquid in scavenge space)
- Control air / servo air low (pneumatic logic fails)
Diagram placeholder:[DIAGRAM: Two-stroke starting air system overview — receivers → SDNR → manifold → distributor → start valves per cylinder]
2.7 Four-stroke reversing & start interlocks (common “permission” faults)
- Clutch/gearbox not in neutral
- CPP pitch not at start interlock position
- Start inhibit from low LO pressure / low control air
- Overspeed trip not reset
- Emergency stop latching
Diagram placeholder:[DIAGRAM: Four-stroke start permissives — LO, JW, gearbox neutral, CPP pitch, overspeed reset, E-stop]
3. Exhaust Smoke & Exhaust Abnormalities
3.1 Smoke colour diagnosis table
| Smoke / Exhaust | What it usually means | Most common causes | Fast confirmation | First action |
|---|---|---|---|---|
| Black | Too much fuel / too little air | Overload, clogged air filter, turbo fouling, poor injector atomization, late timing | High EGT + low scavenge/boost | Reduce load; restore air; check injectors |
| Blue | Lube oil burning | Worn rings/liners, valve guide seals, turbo oil seal leak, overfilled oil-bath filter | Oil consumption + oily exhaust | Reduce load; inspect breather/turbo |
| White (steam-like) | Water/moisture or misfire | Water in fuel, cold start, coolant leak to cylinder | Coolant loss, sweet smell, bubbles | Investigate coolant, stop if rapid loss |
| Grey / haze | Poor combustion quality | Low compression, poor injector pattern | Uneven EGT | Cylinder cut-out test, injector swap |
3.2 Exhaust temperature pattern (per-cylinder)
- One cylinder EGT high → over-fuelling, injector dribble, late injection, poor air to that unit
- One cylinder EGT low → misfire, no fuel, low compression
- All cylinders high → overload, bad scavenge/boost, restricted exhaust, late timing overall
- All cylinders low + smoke → low load instability, poor atomization, cold running
Diagram placeholder:[DIAGRAM: Exhaust temp trend chart — normal band + fault signatures]
4. Low Power / Poor Acceleration / High Fuel Rate
4.1 Split into “air-side” vs “fuel-side” vs “compression”
Air-side (most common at sea)
- Air filter restriction
- Turbocharger fouling (turbine/compressor)
- Scavenge ports / receiver fouling (2-stroke)
- Charge-air cooler fouling (air-side or water-side)
- Exhaust back pressure high
Quick checks
- Boost/scavenge pressure low at same load
- Turbo speed low or hunting
- Charge air temp high (after cooler)
Fuel-side
- Dirty filters / low supply pressure
- Faulty injector(s)
- Pump wear/calibration
- Incorrect timing / ECU fault (common rail)
Compression-side
- Head gasket leak
- Valves not seating / riding
- Rings/liners worn
- Start air valve leaking (yes, it kills compression)
4.2 “Low power” master table
| Likely cause | Why it reduces power | How to confirm | Corrective action |
|---|---|---|---|
| Air cleaner restriction | Less oxygen → incomplete combustion | Low boost + black smoke | Clean/replace |
| Head gasket leak | Compression loss | Bubbles in header, low cyl pressure | Replace gasket, check flatness |
| Injector not sealing in head | Compression leak path | Soot around injector, hissing | Renew sealing washer, torque properly |
| Start air valve leaking | Bleeds compression | Start air line warm, pressure fluctuations | Overhaul/replace start valve |
| Tappets too tight (valves riding) | Valves not closing | No clearance at cold setting | Reset clearances |
| Sticking/broken valve spring | Valve stays open | Low cyl pressure + uneven EGT | Free/repair, decarbonize |
| Pitted valves/seats | Leakage | Leak test, low compression | Regrind/renew |
| Incorrect valve timing | Poor scavenging & charge | Timing marks off | Retime gear/chain |
| Worn bores / rings | Blow-by | High crankcase pressure, oil mist | Overhaul unit |
| Turbocharger fouled | Low air mass | Low boost, high EGT | Water wash/clean, inspect bearings |
| Restricted fuel | Starvation | Supply pressure low | Open valves, clean vent/filters |
| Fuel pump worn/mistimed | Poor injection | Timing check, rack mismatch | Retime/calibrate |
| Exhaust restriction | Back pressure | EGT high + poor response | Clear obstruction |
5. Loss of Lube Oil Pressure / Oil System Faults
5.1 First rule
- Sudden pressure loss: stop now (unless emergency manoeuvring; then minimum speed + shortest time).
- Gradual loss: reduce speed, stabilize temps, find restriction/wear.
5.2 Lube oil fault table
| Fault | Typical pattern | Why it happens | What to check | Action |
|---|---|---|---|---|
| Low sump level | Pressure fluctuates in seaway | Pump draws air | Dip, alarms | Top up, find leak/consumption |
| Suction strainer clogged | Gradual drop | Sludge/contamination | ΔP or pump noise | Clean strainer if possible |
| LO pump drive failure | Instant zero | Sheared coupling/gear | Pump not turning | Stop, repair drive |
| Pump wear | Gradual low | Clearance increase | Pressure vs rpm | Overhaul/replace pump |
| Relief valve stuck open | Low pressure especially warm | Valve hung open | Remove/inspect | Clean/repair spring/seat |
| Filter clogged then bypass opens | Drop then partial recovery | Bypass valve opens | Filter ΔP, element condition | Change element now |
| LO too hot | Pressure low when hot | Viscosity down | LO temp high | Reduce load, clean cooler |
| Bearing clearance excessive | Chronic low + hotter bearing | Restriction reduced | Bearing temps, vibration | Inspect bearing(s) |
| Water in oil | Milky emulsion | Cooler leak / gasket | Purifier, sample | Stop leak, change oil |
| Fuel in oil | Level rises, thin oil | Leaking injectors/pump | Smell, viscosity | Stop leak, change oil |
6. Engine Overheating / High Temps
6.1 Identify which temperature is high
- JW out high → cooling system flow/heat transfer problem
- Exhaust temps high → overload, air shortage, late injection
- LO temp high → cooler issues, bearing friction, oil flow problems
6.2 Overheating table
| Cause | Gradual or sudden | Confirmation | Immediate action | Permanent fix |
|---|---|---|---|---|
| Scale in water jackets | Gradual | Rising temps over weeks | Reduce load | Chemical clean, water treatment |
| Sea water strainer clog | Gradual→sudden | SW pressure drop | Clean strainer | Improve cleaning schedule |
| Thermostat stuck closed | Sudden | No flow to cooler | Bypass/replace | Replace thermostat |
| Pump impeller slip | Sudden | Low flow, pump noise | Slow down | Rebuild pump |
| Engine overload | Sudden/high load | High EGT + smoke | Reduce load | Fix prop/hull/rope |
| Late injection timing | Gradual | High EGT, poor response | Reduce load | Correct timing |
| Head gasket leak | Variable | Bubbles, level loss | Reduce/stop | Replace gasket |
Important: If header tank low and engine hot, add water slowly while running (thermal shock risk).
7. Excessive Vibration / Fluctuating RPM / Hunting
7.1 Vibration (mechanical)
Common sources:
- Turbo rotor imbalance / bearing wear
- Misalignment engine ↔ shaft line
- Damaged prop / rope / cavitation
- Failed flexible mounts
- Misfire on one cylinder
Fast confirmation
- Compare vibration vs rpm (resonance points)
- IR gun on bearings/couplings
- Cylinder cut-out test (where safe)
7.2 RPM hunting (control/governor/fuel)
- Governor oil low/dirty (hydraulic)
- Linkages binding / worn joints
- Load steps too aggressive
- Intermittent injector fault
Diagram placeholder:[DIAGRAM: Governor loop — speed sensor → governor → fuel rack/actuator → engine speed feedback]
8. Crankcase Explosions & Hot Spots
8.1 The triangle in the crankcase
- Fuel: oil mist (worse if fuel dilution)
- Oxygen: air present
- Heat source: hot bearing, blow-by, piston scuffing
8.2 What causes the heat
- Hot bearing (lack of lube/clearance issue)
- Blow-by (worn rings/liners; combustion gas into crankcase)
- Piston scuffing (overheat + lubrication breakdown)
8.3 Correct response (minimum words, maximum safety)
- Do NOT open crankcase doors immediately.
- Reduce load, follow maker/ISM procedures.
- Ensure relief valves functional; investigate OMD alarms.
- Correct root cause before restart.
Diagram placeholder:[DIAGRAM: Crankcase explosion mechanism + relief valve function]
9. Quick Reference — Symptom → Likely System
| Symptom | Likely system | First check |
|---|---|---|
| Won’t crank | Electrical/start | Battery voltage under load |
| Cranks, no fire | Fuel/air/compression | Fuel supply + air filter + timing |
| Black smoke + high EGT | Air shortage / overload | Boost/scavenge pressure |
| Blue smoke | Lube oil ingress | Oil consumption, turbo seals |
| White vapour | Water/cold/misfire | Coolant loss, water in fuel |
| Low power at sea | Air/turbo/exhaust | CAC ΔT, turbo speed, exhaust restriction |
| LO pressure low | LO system/bearings | Level, filters, cooler, relief valve |
| Sudden overheating | Flow control | Thermostat/pump/strainer |
| Vibration rises | Alignment/prop/turbo | Prop/rope, turbo bearings |
| RPM hunting | Governor/fuel | Governor oil/linkages/injectors |
10. Glossary
| erm | Definition |
|---|---|
| Alternator | Generator producing electrical power. |
| Bleeding | Removing air from fluid lines to restore solid flow. |
| Blow-by | Combustion gases leaking past rings into crankcase/scavenge. |
| Circuit breaker | Protective electrical switch that trips on fault/overload. |
| Combustion | Burning of fuel in compressed air producing heat/work. |
| Compression | Pressure/temperature rise as piston compresses air. |
| Contamination | Unwanted foreign material in fuel/oil/water systems. |
| Drive train | Gearbox/shaft/couplings/bearings to propeller. |
| Electrolyte | Battery acid solution (sulfuric acid in lead-acid). |
| Keel cooler | Cooling loop through hull/keel heat exchanger. |
| Relief valve | Valve that opens at set pressure to prevent over-pressure. |
| Sacrificial anode | Zinc/aluminium block that corrodes to protect structure. |
| Scale | Mineral deposits on cooling surfaces reducing heat transfer. |
| Sea water strainer | Filter on SW intake preventing debris entering coolers. |
| Short circuit | Unintended electrical path bypassing load; high current. |
| Thermostat | Temperature-controlled valve regulating coolant flow. |
| Turbocharger | Exhaust-driven compressor increasing intake air mass. |
| Voltmeter | Measures electrical potential (V). |
| Ammeter | Measures current (A). |