Marine diesel engines often originate from commercial vehicle engines (trucks, excavators) – they are fundamentally robust, but one of the main causes of failure is lack of use. If a boat engine is rarely run, the raw water impeller can seize up or belts can harden, for example. In addition, long periods of running at low revs lead to so-called “glazing” (polishing of the cylinder interior surfaces) – modern oils help, but ideally the engine should be run regularly at moderate loads. Another point: installation and marinization (adaptation to the boat) can make accessibility, maintenance, and diagnostics more difficult – it is advisable to familiarize yourself with the engine in advance at the harbor.
Pre-start checks
The following checks should be made before each trip or every morning on tour:
- Visual inspection – Loose or fallen parts, visible leaks, condition of the battery and cables. The engine compartment should be kept clean so that new leaks can be spotted quickly.
- Raw water inlet (seacock, etc.) – Must be open when the engine is running so that cooling water can be drawn in.
- Raw water filter – Remove with seacock closed, check for contamination. If full of dirt/algae, clean and open seacock briefly to flush.
- V-belt – Check the alternator belt, for example, to ensure it is in good condition and has the correct tension. The test: Turn the fan/alternator by hand – it should be difficult to turn and the belt should rotate reliably.
- Expansion tank – Check coolant level: unscrew the cap, place your finger on the rim; the coolant should be at about this point.
- Engine oil – Check oil level with dipstick: first pull it out and clean it, then reinsert it and check. The level should be at the upper mark.
- Transmission oil – Check this as well, but depending on the design, it is often more difficult to access.
- Fuel filter – Check the filter, including the water separator; the diesel should look clean, with no unwanted residues or “diesel bug.”
- Fuel – Check the tank contents, paying particular attention to using marine diesel if possible (lower bio content, less water).
- Driveshaft coupling – Check the connection between the engine/transmission and the propeller shaft: Check that the bolts are tight, turn the propeller shaft by hand – there should be smooth, even resistance, no blocked areas.
- Engine mounts – Mounting points are the connection between engine thrust and the boat. Visual inspection for signs of movement (“skating marks”). Check bolts/grooves and retighten if necessary.
- Throttle and gear linkages – Check the Bowden cables/control cables: securely mounted, no corrosion, so that there is no sticking in forward or reverse gear.
Start procedure
The following points are important when starting:
- Set the ignition to the preheat position (“glow plug”) and wait 10–15 seconds.
- The indicator lights should come on when the key is in the preheat position: oil pressure, temperature, voltage, etc.
- All lights should go out after starting. A short burst of black or white smoke is normal, but it should disappear quickly.
- Check: Voltage >12 V (for 12 V system), raw water drain visible? If no coolant is coming out of the exhaust → stop immediately!
- Warm up the engine: approx. 30 minutes. Operating temperature typically approx. 80–82 °C.
- Check fuel cap/seals: Grease O-ring, keep clean – to prevent water from entering the fuel.
Diagnosis of common problems 🛑
Some typical scenarios with causes:
- Engine won’t start: e.g., dead battery or no connection; air in the fuel system (“air lock”) – bleed correctly; defective glow plugs.
- Overheating: No coolant flow – e.g., strainer clogged, impeller damaged; coolant loss in the expansion tank due to leaky line.
- Loss of power: Propeller wrap – foreign objects or rope around propeller; air filter blocked; sight, belt, and bearing problems.
- Smoke: Blue = worn piston rings/cylinders; black = excessive injection; white = unburned fuel or condensation in cold weather.
- Vibrations: Many causes – air in the system, cylinder problem, engine mounting error, damaged propeller blade.
Assembly/installation instructions
This is particularly true for older sailing yachts: the engine compartment can be cramped and difficult to access. Important components (e.g., impeller housing) should be accessible. If not, install inspection hatches or make adjustments.
Simple tips and practices âś…
- Do not start the engine with the dipstick removed.
- If the dipstick is difficult to access, secure it with string so that it does not lie in the bilge.
- Grease screws and nuts or protect them with Vaseline.
- Do not force parts into place – if something does not fit by hand, it is probably installed incorrectly.
- Empty your pockets (e.g., glasses) before leaning over the engine.
- When working: Remove the ignition key and place it out of reach so that no one can start the engine accidentally.
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