The usual suspects
| Symptom | Likely cause | First action |
|---|---|---|
| Turns over but won't start | Air in the fuel, blocked filter, no fuel | Check fuel; change/bleed the filter; bleed the system |
| Overheating | Blocked raw-water intake, failed impeller, broken belt | Clear the strainer; fit a new impeller; fit the belt |
| Stops or loses power | Fuel starvation, dirty filter, water in the fuel | Change the filter; drain the water trap; bleed the fuel |
| No cooling water at exhaust | Seacock shut, blocked strainer, failed impeller | Open the seacock; clear the strainer; replace the impeller |
| Common small-diesel faults and first actions. |
Bleeding the fuel system
Air in the fuel is the classic diesel stopper: a diesel will not run on fuel that has air in it, and air gets in after a filter change or when the tank runs low. Bleeding removes the air. You loosen the bleed points in order from the filter toward the injectors, work the lift pump until clean fuel free of bubbles comes out, then close each point in turn. Learn your engine's bleed sequence in calm water before you need it in a seaway.
WARNING — Run out of fuel and it won't just restart Running the tank dry lets air into the fuel system, and the engine will not restart until the air is bled out. Keep the tank topped up and know how to bleed the system.
TIP — Work logically, one change at a time Diagnose by the engine's needs — air, fuel, compression, cooling — check the simple, likely things first, and change one thing at a time so you know what fixed it.