Lube Oil & Fuel Systems — Properties, Treatment & Changeover

1. Four Jobs, Two Oils

Lubrication

Films every moving part against friction and wear — mains, crossheads, guides, rods, thrust, chain drive.

Cleaning

Carries dirt and debris away from running surfaces to filters and separator.

Cooling

Holds pistons and bearings inside tolerable temperature, including piston-cooling spaces.

Hydraulics

Works hydraulically actuated exhaust valves as the pressure medium.

Main supply pump draws from the sump and feeds mains, crosshead bearings and guides, connecting-rod bearings, thrust, chain drive and piston cooling. A self-cleaning centrifugal separator works in bypass, drawing sump oil and returning it to the sump after stripping water and solids.

Slow-speed cylinder liners get their own system: high-sulphur fuel makes dilute sulphuric acid on the wall, so special alkaline cylinder oil — dosed to neutralise acid and keep liners clean — is metered by mechanical lubricators to each cylinder and injected between liner and rings on the upstroke.

2. Watch the Sump, Rescue by the Book

Sump quantity holds one safe litres-figure allowing only consumption, losses and refills — any other rise or fall means trouble. Routine health is onboard testing plus sea-going purification, with purifier and filter dirt load telling when intensity must rise.

• System volume through separator: 3× / day
• Rated throughput for polishing: 40%
• Water ceiling before action: 0.5%
• Batch settle before re-purify: 24 h @ 60 °C

Water contamination: at ≤0.5%, run and purify at sea. Above 0.5%, intensify purification or use the renovating tank. For batch treatment, stop the leak, settle the oil and obtain laboratory analysis.

Batch rescue:

1. Find and kill the seawater entry first — purifying into an open leak is bailing a holed boat.
2. Shift the whole charge to the settling tank and hold around 60 °C.
3. Settle about 24 hours, draining water and sludge on schedule.
4. Scrub and inspect the empty sump.
5. Re-purify at optimum temperature and minimum throughput back into the cleaned sump.
6. Shore-test before reuse — the lab rules whether the oil returns to service or needs water-washing treatment.

3. Fuel That Never Sleeps

Change to diesel for a prolonged cold inactive period, major fuel-system repair, drydock or long lay-up — never casually. Reduce load per procedures, secure tracing steam, set viscosity control for the lighter fuel, ease the changeover valve across while watching line pressure, then secure heavy-oil feed and swing returns to the diesel service tank once flushed. Reverse the discipline coming back.

Bowl work lives next door

Gravity-disc selection, start-up proofs and desludge intervals belong to Purifier Operation — Separation, Start-Up & Oil Limits; fuel-ready bunkering practice to the fuel-preparation routine.

4. Fuel Properties — What the Lab Reads Before the Engine Burns It

Characteristics that matter (MOT): viscosity sets heating and injection temperature; CCAI grades ignition quality (high CCAI means lazy ignition — shorten the delay with hotter fuel and correct timing); catalytic fines (aluminium + silicon from refinery cracking) grind pumps, valves, liners and rings; sulphur feeds cold corrosion and steals calorific value (~0.7% per 1% S); asphaltenes block filters, upset purifiers and grow trumpet/petal nozzle deposits (dispersant-dosed); Conradson carbon above ~10% fouls chambers and smokes; ash metals (vanadium, sodium) melt at 480–560 °C into hot corrosion on exhaust valves, while nickel, aluminium, silicon and sand abrade everything they touch:

• Catalytic fines: aluminium and silicon abrade pumps, valves and liners.
• Sulphur: causes acid corrosion and reduces calorific value by approximately 0.7% per 1% sulphur; alkaline cylinder oil counters the acid.
• Asphaltenes: block filters and form trumpet-shaped nozzle deposits; dispersant dosing is used.
• Vanadium and sodium ash: melts at 480–560 °C, attacks exhaust valves and cannot be removed by centrifuging.
• Conradson carbon above 10% produces smoke. Viscosity sets the heater requirement; keep fuel 10 °C above its pour point for pumping.
• Keep settling and service temperatures 14 °C below the flash point; set the engine inlet condition for injection viscosity.

Representative sampling — the analysis is only as honest as the sample

Sample at six points: before the filter, cooler inlet, engine inlet, LO pump inlet, and the two points the book adds for the system under test. One bottle per point, labelled, sealed, dispatched — a single bunker-manifold drip tells you about the manifold, not the engine.

Microbial degradation — the sump grows its own enemies

Anaerobic sulphate-reducing bacteria live without oxygen in sump-bottom water, eating hydrocarbons and additives into acids, stable sludge, corrosion cells and H2S. Signs: rotten-egg smell, choking filters, discoloured oil, crankcase sludge, mud on the sounding tape, yellow crankcase patches, pitted purifier bowl, rust film on the oil, dead additive performance. Prevention: keep LO and purifier running so water never settles, heat the crankcase if the pump stops, test oil on schedule, dose stored oil with biocide.