Troubleshooter: Generate Solutions - PassageMaker
A reliable genset can be essential to comfortable cruising. These skills can save your cruise.

You’re one week into a three-week cruise. You find a nice anchorage for the afternoon and set the hook. Without the breeze you generated underway, the summer heat sets in and it’s time for air conditioning. You press the start switch and the genset cranks but won’t start. Midsummer night’s dream just turned into a nightmare.

While generators make life aboard more comfortable and flexible, they are not without their problems and can be cruise assassins.

Your generator can be described as two unrelated pieces of machinery bound together for a common purpose. One component is a diesel engine. Instead of driving a transmission, this engine drives an armature, a heavy set of windings and magnets. The rotation of this assembly creates a flow of electricity. In most other respects, though, this engine is similar to your main propulsion engine. Any issue that can plague your main engine can also occur with your genset.

Generator problems fall into one of five scenarios: generator won’t crank at all; it cranks but won’t start; it starts but shuts down; it starts and runs but runs unevenly and stalls; or it runs but does not produce electricity. Let’s look at each problem and explore solutions within reach of most boat owners.

Generator Won’t Crank

If nothing happens when you press the start and preheat/bypass switches, then refer to the troubleshooting procedures outlined in “What To Do When Your Engine Won’t Start” (PassageMaker, October 2016). If you find yourself in this situation with your generator, however, one advantage is that unlike a main engine that won’t start, a generator can usually be started using the panel mounted at the generator. Enabling you to bypass the start circuit that runs all the way to the helm station or main panel, this option allows you to circumvent any problems in the associated wiring, connections, and switches. Generators often have a 12-volt circuit breaker mounted on the genset. Make sure that this has not tripped as it can disable the control circuits.

Generator Cranks, But Won’t Start

If your generator cranks but won’t start, this suggests a fuel supply problem. Start with the primary fuel filter and make sure it is clean. Next, check for air in the fuel supply. You can do this by opening the bleed fitting on top of the secondary fuel filter or on top of the injection pump. A small fuel pump, referred to as a lift pump, moves fuel from the primary filter into the injection pump. These pumps might be actuated mechanically (rotation of the engine moves the pump components), or electrically (12-volt current energizes the pump). To check for air in the fuel you must activate the pump with a bleed fitting open. For manual pumps you can manipulate a lever on the pump to move fuel. For an electric pump you will need to press the start and preheat switches to energize the pump.

If fuel escapes but contains air bubbles, you have a leak somewhere in the fuel lines. Perhaps an O-ring on the fuel filter is improperly installed or a fuel-line connection has come loose. All connections from the tank up to the lift pump are on the suction side, and any openings there provide an entryway for air. Check for any problems and repeat the test until fuel without bubbles bleeds out. Tighten the fitting and try to start the genset again.

If no fuel escapes you either have a blockage in the fuel supply or a failed lift pump.

One more possibility lurks. When the genset shuts down it does so by cutting power to an electrically actuated solenoid. For the generator to run, the relay must have power. A poor connection or loose terminal can lead to failure, and in some cases the solenoid itself fails. Check closely for healthy electrical connections.

A failed lift pump will prevent the genset from starting. This electric pump relies on 12 volts to run. If no fuel comes out of the bleed fitting while cranking, this pump has failed or there is a blockage in the fuel supply.  

A failed lift pump will prevent the genset from starting. This electric pump relies on 12 volts to run. If no fuel comes out of the bleed fitting while cranking, this pump has failed or there is a blockage in the fuel supply.  

Generator Starts, But Shuts Down

The most likely scenario might be that the generator has been running just fine and then unexpectedly shuts down. Alternatively, you might find that the genset will start, but when you release the start switches it quickly dies. Both situations point to the same set of problems.

Generators run for long periods of time without the same vigilance that you devote to your propulsion engine. While sleeping with air conditioning running, you probably would not even hear a genset alarm. For this reason, generators come equipped with automatic shutdown mechanisms. These sensors vary among different generators but typically include ones that detect high coolant temperature, low seawater flow, and low oil pressure. On newer gensets the instrument panel will indicate which condition caused the failure, but on many older units, you will have to identify the culprit yourself. Here’s the tricky part: You will have to figure out if a sensor is pointing to a real problem or if the sensor itself has failed.

If the generator has been running and suddenly quits, go right to the genset and carefully put your hand on the water-lift muffler. It should be warm but not hot (you should be able to comfortably keep your hand on it). If that is the case (the muffler is warm but not hot), check the oil level on the dipstick and the coolant level in the plastic coolant recovery container and adjust as needed.

This relay must have power to keep the engine running. Look for loose terminals, corrosion, or chafed wires.   

This relay must have power to keep the engine running. Look for loose terminals, corrosion, or chafed wires.   

If it is too hot, however, you probably have a problem in the seawater flow. While the genset is still hot, check the block temperature with your heat gun (PassageMaker, January 2015). If the temperature is above 200° F, you have a cooling system problem. Both symptoms—hot muffler and overheated engine—point to the same possible causes:

Fouled seawater strainer: Close the seacock, tag out the start switch (PassageMaker, March 2018), and open and inspect the strainer.

Failed impeller: Remove pump cover and inspect.

Blocked intake seacock: Close the intake seacock and remove the top of the seawater strainer. Open the seacock and confirm that you have a good flow of water filling the strainer. If not, you might need a diver, a haul-out, or some clever use of a compressor or inflator to blow air out through the seacock.

What if everything checks out okay? It is possible that you have a faulty sensor. On most older gensets you can disable the sensors by temporarily removing the wires from the sensors. Disable all of them and see if the genset will run. If it does, reconnect them one at a time until it shuts down again and you will have found your culprit. But now you have a new dilemma: If you run the generator with the shutdown sensor disabled, you will have to keep a close eye on the related system. Failing to notice an overheating generator can result in serious damage. Running the generator with a disabled sensor while you are asleep greatly increases this risk. Nonetheless, in some situations, with extra vigilance, this workaround can be helpful.

Generator Runs Unevenly And Then Stalls

This scenario usually unfolds with the generator running smoothly followed by irregular rpm. If the rpm fluctuates and then the generator stalls, the fuel system is the most likely culprit. Refer to the procedures described in the previous section “Cranks, But Won’t Start.”

Abruptly overloading the genset can also cause it to stall. In most cases, the overload will trip the output breaker, relieving the load and allowing the engine to run without a load. In some situations, however, the generator might bog down and stall. If you have been pushing the limits of the genset, turn off some of the heavier loads and try again. It might support three air-conditioning units without difficulty, but if the water heater and battery charger happen to cycle on, you can easily overload the generator.

Poor performance can also point to restricted air intake. Many sound enclosures utilize an exposed foam that degrades over time. Dust and particles from failing insulation can clog the air filter and reduce performance. Inspect and clean the air filter as needed.

Generator STARTS, Then DIES When You Release the Preheat and Start Switches

This one can be perplexing. Since it starts reliably but immediately shuts down, we can rule out fuel and temperature issues. This failure might be triggered by your fire suppression system. A properly installed engine-room fire extinguishing system will shut down the engine and the generator just prior to dispensing the firefighting chemicals. These chemicals will not shut down a running diesel engine and if left running the machinery will ingest the firefighting agents, diluting the concentration. This critical system can malfunction, preventing the genset from starting. Make sure the green light on the fire system control panel is on. If not, you might have a blown fuse or a faulty unit. Disabling the firefighting system is not a good idea, but if you have the installation manual you can probably temporarily disable the connection to the generator to confirm the source of the problem.

If the fire extinguishing system is working, the shutdown switches described earlier might also be the cause. These switches work by either providing voltage or turning off voltage at a shutdown relay. In most cases, when all conditions are acceptable, this relay stays energized and allows fuel to flow. If a sensor finds a problem, it shuts down the voltage to the relay, which in turn cuts off fuel to the generator. Locate the relay and check all connections for looseness or corrosion.

Generators rely on shutdown sensors to automatically stop the genset in the event of a problem. In some cases, the sender itself, such as this coolant temperature switch (red arrow), can fail. The green arrows indicate bleed points for the fuel system.

Generators rely on shutdown sensors to automatically stop the genset in the event of a problem. In some cases, the sender itself, such as this coolant temperature switch (red arrow), can fail. The green arrows indicate bleed points for the fuel system.

Generator Starts and Runs, But Produces No Electricity

As always, start with the obvious. Have you properly switched over at the main electrical panel? If you were on shore power, have you switched over to the generator? If the panel has been properly configured, have a look at the generator. To protect against overloads, the generator has a circuit breaker mounted inside or just outside of the sound enclosure. This breaker will be the one that looks like two breakers joined together: a double-pole breaker. Find the breaker and if it has tripped, reset it. The setup also includes a DC breaker or fuse to protect the generator control circuits. Check this one as well.

When the genset runs but has no output, look for a breaker like this one mounted on the generator. This breaker protects against an overload from high demands.

When the genset runs but has no output, look for a breaker like this one mounted on the generator. This breaker protects against an overload from high demands.

Conclusion

When it comes to gensets, don’t let “out of sight” mean “out of mind.” Your generator needs as much attention as your main engine. Routinely inspect the belt tension and look for raw-water or coolant leaks that indicate a developing problem. If the foam sound insulation starts to break down, remove all of it and replace it with new material. Pay close attention to the exhaust elbow. The combination of high heat, saltwater cooling, and in many cases questionable alloys often leads to failure.

If your genset does quit, don’t give up. Many problems can be solved on board with a bit of resourcefulness. The troubleshooting procedures outlined in this article are within reach of every cruiser—and they just might save your cruise. 

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