Is It Risky to Let Your Portable Generator Run Out of Gas? – Spruce Generator (2023)

A portable generator is always a savior during a power outage or when you need an outdoor power supply, especially in a remote area. But one of the disadvantages of using a portable generator is that you need enough fuel. And if you do, you still be concerned by the question, “is it bad to run a generator out of gas?”

The short answer is YES. When you wait for your generator to run out of gas to refuel it, you risk damaging the generator itself and your appliances. There might be voltage fluctuations, and the generator might lose the residual magnetization necessary in producing electricity. Next time you start the generator, its engine will run normally, but there will be no voltage produced.

Can you fix the generator magnetism loss? Can you prevent your generator from run out of gas? How do you start a generator after it runs out of gas? Read more to get these answers and more.

What Are the Risks of Running a Generator Out of Gas?

As mentioned above, when you run your generator until the last drop of fuel in the tank, you risk damaging your appliances and the generator itself. It’s not something to be worried about much, but it’s something you might want to avoid if you can.

Loss of residual magnetization

If you’re using a gasoline generator, you’re unlikely to run into low fuel problems. These generators rely on gravity which pushes the fuel into the engine from the tank. When it’s burnt, it drives the alternator rotor to produce electricity.

However, you should be worried about your generator losing residual magnetization. If you run your generator out of gas day after day, there is the chance it will not produce any electricity the next time you start it. It’s a common problem in diesel generators, but you can also experience it in portable gasoline generators.

How does this happen? When you run a generator out of fuel with appliances connected, they continue to draw any small voltage left in the generator line. Before you realize it, they have consumed all the residual magnetization.

What is residual magnetization? How a generator works are by rotating a set of magnetic conductors through an electromagnetic to produce electricity.

Residual magnetization ensures the electromagnetic parts work during every generator start to produce enough power-producing electromagnetic field. When consumed, the generator starts as usual, but the voltmeter read zero.

It’s easy to fix the problem with a drill or a 12v battery, something we will look at later.


There is also a risk of fuel pump overheating if your generator uses one to supply fuel to the engine or runs a fuel injection system.

The fuel cools down the fuel pump in the gas tank. When the fuel is low, or the tank is almost empty, the pump will start pulling a high amount of air, which cannot cool the fuel pump.

However, this happens quickly, at least until the engine stops running and everything, including the fuel pump, stops. But if this was to happen more than once, it can reduce the fuel pump’s lifespan.

Damages to the Connected Appliances

Waiting until your generator runs out of fuel also exposes your connected appliances to damages, especially sensitive electronics such as sound systems, computers, and the likes.

When the generator pulls a small amount of fuel mixed with air, it will run the engine with varying speeds, changing almost instantly.

When that happens, the output voltage will also fluctuate; there will be voltage highs and lows. The fluctuations can cause lasting damages to your appliances.

How to Fix Damage Caused When a Generator Runs Out Of Gas

How to Flash (Re-Magnetize) Generator

If you allowed your generator to run out of gas without knowing twice or thrice recently, then you might experience the issue of loss of residual magnetization.

And as I mentioned earlier, the problem can lead to your generator starting as usual, but it doesn’t produce any voltage.

Fixing the problem is easy; all you need is to re-magnetize or flash your generator. You can use either a corded drill or a 12-volt battery.

How to Use a Drill to Flash a Generator

Step 1: Hook up the drill cord to one of the AC outlets on your generator and turn on the generator.

Step 2: With the generator running, turn the drill chuck on the reverse (opposite direction) while pressing the drill’s trigger.

Rotating the drill chuck in reverse sends current to the generator alternator, thus restoring the lost residual magnetization. However, the method isn’t that reliable.

How to Use Car Battery to Flash Generator

If the drill method didn’t work, get a car DC generator and follow the following steps:

Step 1: Use your generator user’s manual to locate its voltage regulator. There are two wires, a white or red wire and a black wire, connecting to the generator brushes.

Step 2: Unplug those wires from generator brushes and connect them to the battery’s positive and negative terminals marked with (+) positive and (-) negative.

Refer to your user manual to know which wire connects to the positive terminal and the one that connects to the negative terminal.

Step 3: Start your generator and allow the engine to run for about three seconds or so. While it’s running, don’t touch the voltage regulator as there is the risk of getting shocked.

Step 4: You can now turn your generator off and disconnect the battery and return the wires to the brushes.

Step 5: Start your generator now. It should work after this process.

How to Prime a Diesel Generator

If you’re using a diesel generator, you need to prime it before starting it again. The process is referred to as ‘bleeding.’

It’s essentially the process of removing any air sucked into the fuel pump when the generator was running on fumes. The air might not allow the pump to prime so that no fuel will be reaching the engine.

Your generator’s user manual should have a rundown on how to bleed it successfully. The user manual is there to make you familiar with your generator, its part, and give you easy fixes to common problems.

If the manual is unavailable or it seems complicated for you, here is simplified steps on how to bleed your generator:

Step 1: Fill the gas tank with enough diesel; a level higher than its fuel filter would be better. It needs to move into the fuel filter filling it.

Step 2: Loosen the nut on the fuel filter top using a wrench to ensure the diesel drains rushing out any air inside it.

Step 3: Give it a minute and then seal the fuel filter by returning the nut and tightening it using the wrench.

Step 4: Crank the generator without starting the engine. This helps build enough pressure inside the fuel pump.

Step 5: Locate the generator’s fuel injector system and loosen the injector nuts to let the air out. Do the same to all the injectors, one at a time. Once the air is leaked out, tighten the nuts back in place.

Step 6: Repeat this process until you bleed all the air sucked into the fuel line.

Step 7: Start your generator now. Cracking it shouldn’t be a problem now.

The bleeding process is quite similar to various models. It should take you few minutes to get your generator operational again.

If there is something different, refer to your user manual. If not available, you can get it from your manufacturer’s website. You can also call customer support for some help.

How to Make Sure Your Generator Doesn’t Run Out Of Gas

All the above problems are avoidable if you know how to make sure your generator never runs out of gas. You can:

Set a timer

Filling the fuel tank gives you a better estimate of how long your generator will run under a specific load. Check the generator manual to know its run time.

If your generator takes 4-hours to consume a full tank of fuel at half or full load, set a time within that range.

Once your timer rings, you can open the fuel tank and check how much fuel there is without shaking the generator, especially when running.

If your generator has a working fuel gauge, you don’t need to open the fuel tank. The fuel gauge can tell you the amount of gas remaining.

If too low, shut the engine off, allow it to cool a bit and get the extra fuel can and refill it.

Ensure You Have enough fuel

If you’re getting ready for a hurricane, get enough fuel from the gas station. It’d be best to have more than one gas can if you anticipate the hurricane to cause a power outage that can last hours.

The same applies when you go camping. Carry enough fuel with you. If you think you will take longer than the generator’s run time, carrying extra fuel can help you stay ready for any emergency.

Can You Refill Your Generator While It’s Running?

Is it bad to run a generator out of gas? Yes! But that doesn’t mean you can take the gas can and try to refuel the generator while running.

You must NEVER refill your generator fuel tank when it’s running or when still hot. That might lead to fire or explosion, and as you can guess, that won’t go well for you and your generator.

Avoid injuries and damages by refilling it when it’s off. If the gas tank is almost empty, unplug the load and shut off the generator. Give it a minute or so for it to cool down and then refuel it.

How to Start a Generator after Running Out of Gas

Most of the time, if you run the generator out of gas, you might have problems starting it. I don’t mean the two problems I discussed before. If your generator ran out of gas now won’t start, few starting issues might be giving you a hard time. It would be best if you were to start your generator with the following steps.

Steps to Follow:

Step 1: start by refueling the generator with ‘good’ gas. If your gasoline has been sitting in storage longer than three months without preservatives, it’s no longer useful. You can check it; if it looks cloudy, it’s ‘bad’ gas.

Step 2: After you’ve refueled the generator with ‘good’ gas, you can crack the generator. If nothing is happening, engage the chock and start the generator while making sure the fuel gauge on the fuel tank cap is on.

Step 3: If your generator runs slightly sluggish, don’t worry; it’s normal. If you’re still having a problem starting the generator, play with choke. However, when the engine reaches a rhythm, slowly release the choke to the off position.

Step 4: If the generator is still not starting, you can try re-magnetizing it or priming the pump if it’s a diesel model. If you’re not a success, try troubleshooting other areas like bad spark plugs, clogged fuel filters, bad coils, or dirty air filters.

Related Questions

How long should I run my portable generator?

You can run your portable generator until the next refueling. However, if your generator runs on a huge propane tank, it’d be best to give it a cool-down break. It can be 4-, 8- or 12-hour intervals.

Bad Gas in My Generator. How Do I Remove It?

It’s easy; turn on the fuel valve and drain every drop of the fuel out of the generator. Shut off the fuel valve and close the fuel tank. Locate the carburetor (use your user manual) and remove the drain bolt. Allow the remaining gas to run out.

Final Verdict

Is it bad to run a generator out of gas? Yes. Time your next refueling and have an extra can near. Never refill the generator when it’s running. If you ever experience a problem where the generator runs okay but does not produce any voltage, try flashing it use a drill or a 12-volt DC battery.

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