Factors Affecting the Continuous Runtime of AC Generators

Buying a standby generator for your home or business is an excellent investment. But making it run for the most number of hours is another matter altogether.

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One of the most common subjects on AC generators on the web is how long a diesel generator runs.

You might follow what manufacturers say. That a standby generator can run for 500 hours non-stop.

But to tell you the truth, though, there is no standard answer to this question. Even the 500 hours depends on many things, which we will discuss later.

Thus, we cannot tell you that your generator will run for days, weeks, or even months. Also, it is hard to say how long the lifespan of your generator will be.

When you fire up the generator, so many things happen. They all determine how long it will run and how long it will last.

But yes, you can prolong the runtime of your generator as much as possible. Consider the factors that affect the runtime of AC generators.

Keep reading to see them:

6 Factors Affecting Continuous Runtime of AC Generators

By design, standby AC generators can run for days on end as long as they have enough fuel. But even then, here are things that might affect your generator’s running time.

1. The type of generator

Needs we say that if you need a generator that can run for days without stopping. Will, it is not a portable type? It will have to be a standby type and a diesel one at that.

Standby generators come with large motors, long-range fuel tanks, and large coolant reservoirs. In some cases, the manufacturers say their generators can do up to 500 hours of non-stop running time. That is three weeks of a generator’s runtime!

Before you buy one, look for information about generators. You will find those huge industrial ones that can even run for years without stopping for too long. They can run even for weeks to a few months without the need to add oil or service them.

Even with small commercial generators, it is possible to add an oil view. This lets you know how much oil remains and add more while it is still running. This requires the input of a technician, but you will get the total value of your investment.

A small, portable generator is not going to last many hours. In any case, it does not have a big enough tank to hold fuel that can enable it to run for 24 hours.

Find out the manufacturer rating of the generator. Are you using it for suitable applications? If yes, it can run for days on end.

Even then, you will still need to stop the generator at some point. It can also be for a couple of hours for servicing and overhaul. In that case, if your business relies on a generator alone, you might need a second one.

Why does the type of generator matter so much? The bigger ones can run for hundreds of hours (up to 500) without a break or with a few breaks between. The small, portable ones can hardly run for 48 hours non-stop.

2. Quality of the wearable parts

An AC generator is not much different from a vehicle’s engine. Thus, there are so many moving parts, including fans, belts, and others. These parts wear out with time. If you do not stay on top of their condition, they could give up on you when you least expect them.

The generator also has many other wearable parts. These include oil filters, air filters, and diesel filters. If one of them is not clean or has some different sort of damage, it will affect the runtime of your generator.

If you wish to prolong the runtime, check these parts. Ensure they are always in good working condition.

Check the air filter for dust and other debris. Change the oil filter when you are servicing the generator. Old, sludgy oil can affect how the oil circulates in the engine. Always use clean diesel so that the fuel filter does not collect debris.

The generator has to run from time to time. Even if you do not need it, it is best to run it for some time every week. You can even run it without load so that oil and coolant can circulate.

Check with the manufacturer to know how to prolong the life of the wearable parts. This can depend on the average load size. But most of the time, it depends on more things, including ambient running temperature.

3. Low-quality fluids

Always use the coolants that the manufacturer recommends. Not all generators are the same. So you are supposed to check the user manual to see the service intervals. You will also see the parts to service and, most, the types of fluids that you need to use.

On top of using the correct coolant, you also need to maintain the recommended levels of the same. What do you need to do for the wearable parts to last a long time? For the last about 250 hours, the generator has to run at 60 to 70°C.

If the coolant is not enough and not of the best quality, the generator’s temperature can rise too much. This will affect the wearable parts, and it will cut short the runtime of the generator.

If you maintain the correct coolant level, you can prolong the lifespan of the parts. You might even be able to run your generator for a consistent 100 hours, with a couple of one-hour breaks.

4. Fuel and oil

By adding fuel to the tank, you can keep the generator running for a long time. The continuous runtime of the generator also depends on the oil a great deal.

But for most small models, you cannot add oil while the generator is still running. Thus, you will need to give the generator a few breaks to cool down to give you time to add more oil.

We can say that the generator will run for as long as it has fuel and oil.

If the generator uses up all its oil, the engine will seize, and it will stop working. Having fat in the generator’s oil sump and having diesel in the fuel tank will keep the generator running. It can run even for 200 hours.

The best way to know that the sump is not dry is to use an app. Most manufacturers of large industrial generators have user apps.

An App can keep you up to date with alerts on the oil and fuel status. That way, you can enjoy prolonged runtime for your generator.

Some people ask: Can a generator run 24/7? It can if all the parts are in good condition. But it is good to give it a break of about 15 minutes after about 7 to 10 hours. That way, if you need to add oil, you can do it.

You can also check the coolant level so that you can do it during the break if it needs topping up. You also need to note something else. The frequency of the breaks might depend on the load that you are running on the generator.

You could also buy a GenSet that has modern safety measures. It will go into limp mode or shut itself down completely to protect itself from damage.

If the coolant level runs low or the oil sump goes dry, the generator can shut itself down. Thus, to ensure that it runs, keep all the fluid levels up.

5. Running light or no load affects the runtime of a generator

Most people think that running a generator on a light load can increase the runtime. This is a mistake! It might, but at the same time, there will be other issues to contend with. These include things like soot buildup in the system.

Experts recommend running a generator 24 hours non-stop at a 70 percent load. This is an average, so it might even run at 60 to 80 percent load.

Your generator could also develop a problem of wet stacking. This is when your diesel generator starts to drip a thick black liquid from the exhaust. Such happens when you run the generator on a very light or no load.

If generator wet stacking occurs, it affects the performance and runtime of your unit. When you do need to run it at its average load, the runtime will reduce.

6. Maintenance status

Generators need constant maintenance at regular intervals. During maintenance, you can change some parts. These include belts, air cleaners, fuel filters, oil filters, and others.

Stay up to date with the maintenance of your standby GenSet. It can run for the 500 hours that most manufacturers say without up-to-date care. The generator’s runtime can decrease to even less than 200 hours.

As you replace the wearable parts, use the ones that have a higher runtime rating. They might cost more money, but they are worth it.


Buying a standby generator for your home or business is an excellent investment. But making it run for the most number of hours is another matter altogether.

Now, you can see the factors that affect the runtime of your standby diesel generator. You can milk as much runtime as possible.

Stay on top of its maintenance. Also, keep it in a place that has enough air circulation and run it at 70 percent load at all times.

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Hey all, I'm Baymax Yan, working at a generator manufacturer and Having more than 15 years of experience in this field, and I belives that “learn and lives.” The sure thing is that I can often help my work. So I have created the blog to share all my knowledge with you. Hope my sharing helps!

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