Saltwater Ingress and Hydrolock Repair in Australia
Seawater inside a marine diesel is the most time-critical problem on this site. Damage is measured in hours, not months, and what you do in the first day determines whether the outcome is an oil change or a rebuild.
If it has just happened: do not crank the engine
Water does not compress. If there is water on top of a piston, turning the engine over bends connecting rods and can crack a piston or the block. A hydrolocked engine that has not been cranked is often recoverable; one that has been cranked frequently is not.
Do not try to start it. Do not turn it over “just to see”.
Emergency first steps
The order matters:
- Stop. No cranking.
- Remove the injectors or glow plugs to open the cylinders, so any water has somewhere to go.
- Turn the engine over by hand using the crankshaft, expelling water through the open ports.
- Fill the cylinders with oil to displace remaining water and prevent rust. Bare cylinder bores rust in hours in a marine environment.
- Change the oil, repeatedly. Seawater in the sump is corroding bearings the whole time it is there.
- Get a mechanic. This is a triage sequence, not a repair.
Every hour that seawater sits in an engine is bearing, bore and valve damage. A prompt response can save an engine; a weekend of waiting usually does not.
How the water got in
Finding this out is not optional — a repaired engine on an unrepaired cause floods again.
Exhaust system. The most common route. A corroded or blocked exhaust elbow, a riser that is too low, an inadequate exhaust loop, or a following sea pushing water back up the exhaust while the engine is stopped. → Exhaust elbow replacement
Aftercooler. A perforated seawater-cooled aftercooler puts water directly into the intake. → Aftercooler service
Heat exchanger or oil cooler. A perforated tube stack mixes seawater with coolant or oil. → Heat exchanger service
Head gasket or cracked head, letting water into a cylinder.
Cranking an engine that will not start, pumping raw water through the exhaust into the cylinders — which is why a persistent no-start on a marine diesel should not be met with more cranking.
Swamping or a knockdown.
Assessing the damage
- Oil analysis for salt and water content
- Compression and leak-down testing
- Borescope inspection of bores and valves for rust and pitting
- Bearing inspection — often the deciding factor
- Checking for a bent rod after any cranking
Outcomes range from repeated oil changes and inspection through to a full rebuild, and the honest determination requires opening the engine.
→ Marine engine rebuild · Saltwater in the engine oil
What it costs
The widest range on this site — determined almost entirely by how quickly it was addressed.
→ Saltwater damage repair cost
Find saltwater ingress repair in your city
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Frequently asked questions
My engine won’t turn over — should I use a bigger battery? No. An engine that will not turn may be hydrolocked, and forcing it bends rods. Find out why before applying more force.
How quickly do I need to act on seawater in the oil? Immediately. Salt water corrodes bearings continuously while it sits. Hours matter.
Can an engine recover from ingesting seawater? Frequently, if it was not cranked and was treated within a day. The same engine left a week is usually a rebuild.
Why does my engine keep taking water in? Almost always the exhaust system — a corroded elbow, or an installation geometry that lets water back to the engine. The cause must be fixed or it recurs.
Should I keep cranking a marine engine that won’t start? No. On a raw-water-cooled engine, cranking pumps water through the exhaust and it can back up into the cylinders. Diagnose instead.