A generator that shuts down is protecting itself. The control system has seen something outside its limits and stopped the engine before it does damage. The fastest route to a fix is to work out which protection tripped, so before anything else, read the display and write down or photograph exactly what it says.
Most marine generators report the same handful of shutdowns. Here's what each one usually means.
High coolant or high exhaust temperature
This is by far the most common, and nine times out of ten it's raw-water flow.
A generator runs at a fixed load for hours in warm water, so any restriction in the seawater circuit shows up quickly. In rough order of likelihood:
- A blocked strainer. Weed, plastic bags and, in the Balearics, loose Posidonia leaves.
- A worn or failed impeller. If vanes are missing, the pieces will be in the heat exchanger or the pipework after the pump. Changing the impeller alone won't cure it until they're out.
- A partly closed seacock. It happens more often than anyone admits, particularly after a haul-out.
- A scaled or blocked heat exchanger. Flow is down even though the pump is fine.
- A restricted exhaust mixing elbow. Carbon and corrosion narrow the elbow until the cooling water can't get through.
What crew can check: with the generator stopped, close the seacock, open and clean the strainer, reopen the seacock and check water flows in. Start it and watch the exhaust outlet. You should see a good, steady flow of water mixed with the exhaust. If the flow is weak, the problem is between the strainer and the outlet.
If you're trained and confident changing an impeller, carry a spare and do it. Otherwise, leave it to us.
Low oil pressure
Stop and check the oil level with the engine off and level. If it's low, find out where it went before topping up and restarting. Look for oil in the drip tray or the bilge.
If the level is fine and the generator still trips on low oil pressure, it's either a sender or switch fault, or a real loss of pressure. Don't keep restarting it to find out which. If the pressure really has gone, every restart does more damage. That's a job for a technician with a test gauge.
It cranks but won't start
With no alarm and no start, the likely suspects are fuel and air:
- A fuel valve left closed, or a tank switched over to one that's empty.
- A blocked fuel filter, or air in the system after a filter change.
- Glow plugs (on smaller generators) or the fuel stop solenoid.
Don't keep cranking. On a wet exhaust, every crank pumps raw water into the waterlift muffler, and with no exhaust pressure to push it out, it can work its way back into the engine. Two or three attempts, then stop and call us. Water in the cylinders is a far bigger job than a fuel problem.
It runs, then stops without an alarm
This is usually fuel starvation: a filter loading up, a pick-up in a low tank sucking air in a swell, or an air leak on the suction side. If the generator hunts or surges before it stops, that points the same way.
Overspeed, underspeed or frequency faults
These come from the governor, its actuator, or the speed sensor. They can also be caused by large loads switching on and off. A watermaker and three AC compressors starting together can pull the speed down far enough to trip a protection. Starting heavy loads one at a time often makes the problem go away.
On variable-speed generators such as the Fischer Panda iSeries or WhisperPower's Genverter range, the inverter manages output, so the fault codes are different. Write down the code exactly; the manufacturer's code list is what we work from.
A breaker trips, but the engine keeps running
That isn't an engine shutdown. It's an electrical overload or fault downstream. Switch off the big loads and reset. If it trips again with only light loads on, there's a fault on that circuit that needs tracing.
Water in the oil
If the oil on the dipstick looks milky or there's more of it than there should be, stop. Don't restart. Possible causes include water getting back through the exhaust, a failed anti-siphon valve, or a heat-exchanger or gasket failure. All of them need a technician before the generator runs again.
What to send us
If you book online or message us, include:
- the make, model and running hours of the generator;
- the exact alarm text or code;
- what was running when it stopped (air conditioning, watermaker, galley);
- a photo of the exhaust outlet with it running, if it will run;
- where the yacht is.
We service Onan, Fischer Panda, Kohler (now sold as Rehlko) and WhisperPower generators on board across Mallorca and the Balearics. See our generator service page, book online with photos, or call the 24/7 line on +34 971 251 374.