Why does my inboard diesel keep running after I turn it off?
My yacht's inboard diesel keeps idling after I turn the ignition key off, although the instrument panel goes dead. Is that normal, or should I be checking the stop cable or fuel shut-off solenoid?
Answer
Your inboard diesel keeps running because turning off the key has not stopped fuel delivery; on many older installations, a separate stop cable or button stops the engine. If the key used to stop it, check the fuel-stop linkage and electrical stop circuit first; an engine that suddenly races and produces heavy smoke needs urgent action.
Check the shutdown procedure
A diesel ignites fuel through compression and needs no ignition spark to keep running. On a mechanically controlled engine, the key may only supply power to the instruments, warning alarms and starting circuit.
Identify the engine model and panel arrangement before replacing parts. Common arrangements include:
- Pull-to-stop cable: a cockpit handle moves a stop lever on the injection pump.
- Separate electrical STOP button: a solenoid moves the fuel-stop mechanism when the button is pressed.
- Key-operated shutdown: turning the key off operates a stop circuit or removes power from a fuel-control solenoid.
The arrangement depends on the engine model, production year and any replacement control panel. A dead instrument panel shows only that its electrical supply has switched off. It does not prove that the injection pump has stopped delivering fuel.
With a separate stop control, select neutral, allow the specified cooling period, then operate the stop control until the engine stops. Switch off the key afterwards. Yanmar's 2018 YM instructions recommend five minutes of idling without load before shutdown.
Inspect the cable and stop lever
If the engine stays at normal idle, check that the stop control moves the injection-pump stop lever through its full travel. A loose cable clamp, slipped outer sheath or seized cable can let the handle move while the pump lever barely moves.
Keep hands, clothing and tools clear of belts, pulleys and hot exhaust components during any running check.
- Find the designated stop lever in the engine handbook. Do not confuse it with the throttle lever.
- With the engine stopped, ask someone to operate the cockpit handle while you watch the cable, its mounting bracket and the lever.
- Check for a loose cable nipple, broken strands, corrosion and an outer sheath moving in its clamp.
- Confirm that the lever reaches its specified stop position and returns fully to the running position.
If the handbook gives a manual stopping procedure and the lever is safely accessible, use it to stop a normally idling engine. If operating the lever directly stops the engine but the cockpit control does not, the fault lies in the cable, mounting or adjustment. Do not alter sealed injection-pump screws or governor settings.