Common marine diesel questions
264 questions boat owners actually ask, answered plainly and grouped by topic. Every answer links to the guide it comes from if you want the full explanation.
Overheating and cooling
Impellers, heat exchangers, exhaust elbows, strainers and the raw water circuit — the system behind most marine engine failures in Australia.
- How often should an aftercooler be serviced?
- How do I know if my aftercooler is leaking?
- Does my aftercooler have an anode?
- Why does an aftercooler matter more on a boat than a truck?
- How often should the exhaust elbow be inspected?
All 28 questions on overheating and cooling
Fuel, tanks and diesel bug
Contaminated fuel, microbial growth, blocked filters and water in the tank — on a boat the tank causes more trouble than the engine.
- Will a biocide alone fix it?
- Why did my filters get worse right after treatment?
- Can I prevent it entirely?
- Is diesel bug worse in Australia?
- How do I know it's the bug and not just dirty fuel?
All 24 questions on fuel, tanks and diesel bug
Gearboxes, sterndrives and shafts
ZF and Twin Disc gearboxes, sterndrive bellows, stern glands, shafts and alignment.
- How often should engine alignment be checked?
- Can alignment be done on the hard?
- What are the symptoms of misalignment?
- My boat vibrates — is it the propeller or the alignment?
- Do engine mounts need replacing at the same time?
All 25 questions on gearboxes, sterndrives and shafts
Rebuilds, repowers and major work
When to rebuild, when to repower, what a reconditioned engine really is, and what saltwater ingress costs.
- How do I know it's the head and not something cheaper?
- Can a corroded marine cylinder head be repaired?
- Do head bolts need replacing?
- Why did my head fail?
- Rebuild or repower?
All 38 questions on rebuilds, repowers and major work
Servicing, layup and recommissioning
Service intervals by hours and by calendar, winter layup, recommissioning, and why low hours is not good news.
- How often should anodes be replaced?
- Does my engine have anodes inside it?
- Zinc or aluminium?
- Why are my anodes disappearing so fast?
- Can I paint over anodes when antifouling?
All 28 questions on servicing, layup and recommissioning
Buying a boat and engine surveys
Pre-purchase engine inspections, sea trials, and the findings that should change your offer.
- Isn't the engine covered by the general marine survey?
- Do I need a sea trial?
- The seller has warmed the engine up for me — is that a problem?
- What if the survey finds problems?
- Are low hours a good sign?
All 9 questions on buying a boat and engine surveys
Finding and choosing a mechanic
Which trade does which job, mobile versus workshop versus haul-out, and what to ask before booking.
- What should I do first when the engine stops?
- Can I keep motoring with an overheat alarm?
- What is the most useful repair to learn?
- Is it cheaper to be towed or repaired on the water?
- My engine stopped and won't turn over — what now?
All 29 questions on finding and choosing a mechanic
Commercial, charter and workboats
Survey obligations, downtime economics, and how commercial operators maintain engines differently.
- How often should charter engines be serviced?
- Why replace parts that still work?
- What is the most common charter engine failure?
- When should major work be scheduled?
- Does oil analysis make sense across a fleet?
All 20 questions on commercial, charter and workboats
Questions by location
Local conditions, seasonality and access, from the Gold Coast to Port Stephens.