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How long can a diesel generator run continuously for?

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If you own or are thinking about buying a diesel generator, you may be wondering how long you can run the generator continuously.

Diesel engine generators are usually the preferred choice if they are to potentially run for extended periods because they can be bought with huge long range tanks. This means you’ll be able to get more in a single fuel tank making a diesel engine generator more suitable for continuous use.

The more efficient choice

Diesel generators also have more efficient motors. They will use less fuel than petrol generators over time so are cheaper to run. This is especially beneficial if the generator is being used for prolonged power outages.

As we take a further look into the running time of a generator, it’s worth remembering that every generator is different and all require regular maintenance. Make sure you check the user manual for a new generator before you get started.

Throughout this article we look at why diesel generators are better for continuous power and answer the question, how long can you run a generator continuously?

Can you run a diesel generator continuously?

When it comes to diesel, if you are going to run a generator continuously there are a few things you’ll need to consider depending on the type of generator you own.

A limiting factor with a portable generator is the size of its fuel tank. For portable generators to be portable they tend to have smaller tanks, meaning you’ll have less fuel so your run time will be effected by needing to stop the generator, cool down the engine, and refill the tank.

If you have a standby generator or a portable generator you can buy a larger fuel tank to help with the fuel supply meaning the running generator can produce power for longer.

What limits a generators running time?

With any generator you are limited by it’s rated runtime. This is what signifies how much power a generator can supply under what’s considered its normal working load. You’ll need to check this to ensure you’re buying the right generator for the job.

Finally, if you are running diesel generators continuously you’re going to require more regular oil changes. Generators that run low on engine oil can face serious problems. Make sure you check your levels on your generator regularly.

Check out our guide to which type of oil you should use for your diesel generator here.

What is considered high hours on a diesel generator?

A diesel generator can last between 10,000-50,000 hours before needing servicing. However, a smaller portable generator will be limited to 2,000-3,000 hours due to its size.

Factors such as the generator type, load on the generator, and environmental conditions such as extreme weather, all come into play.

Typically portable generators run will happily run for a few hours continuously, 16-18 hours are considered high hours.

Can standby generators can run for longer?

Standby generators not limited by fuel supply can run continuously for for up to 500 hours, this is 3 weeks of continuous use. This is dependent on your standby generator’s manufacturer recommendations, but at 21 days it is recommended you allow you standby generator to cool and perform general maintenance.

Evopower diesel generator

How much diesel does a generator use per hour?

Whether you’re using standby generators or a portable generator, you’ll need to workout how much diesel your generator uses per hour so you can estimate how long can you run a generator before it needs more fuel.

What affects how much diesel is consumed?

Generators have a fixed RPM, so to work out the fuel consumption you need to consider the load you’re putting on the generator, e.g. the amount of equipment or appliances you plan to run on its power.

How to calculate

Below is approximately how many litres per hour you can expect to use given the size and output of the engine and the load placed on the generator.

Generator Size/ Approximate Diesel Fuel Consumption¼ Load(Litres/hr)½ Load(Litres/hr)¾ Load(Litres/hr)Full Load(Litres/hr)
8kW / 10kVA1123
10kW / 12kVA1234
12kW / 15kVA1234
16kW / 20kVA1345
20kW / 25kVA2356
24kW / 30kVA2457
32kW / 40kVA35810
40kW / 50kVA36912
40kW / 50kVA591419
60kW / 75kVA7121825
120kW / 150kVA8162432
160kW / 200kVA10203040
200kW / 250kVA13253850
280kW / 350kVA19385675
400kW / 500kVA275380106
640kW / 800kVA4386129172
800kW / 1000kVA60110170220
1000kW / 1250kVA65130194259

What are the long term impacts?

Running Diesel engines for several days continuously can have some long term impacts. Firstly the general upkeep needed is going to be greater. Keeping on top of it will greatly extend any generators lifespan.

You also need to think about whether the generator will be adequately loaded during its run time. A few hours won’t be a problem, but if you run a generator on a light load for an extended period, you risk what is known as wet stacking. This is when a black oil like liquid drips from the exhaust joints, because the engine is sending unburned fuel into the exhaust system.

Finally, diesel fumes from a generator aren’t good for the environment or people, so consider whether your generator really needs to run continuously and make sure it’s well ventilated.

Are there alternative options to diesel generators

Alternative fuel supplies such as natural gas generators, are able to run for longer due to being connected to a gas line with a continuous supply of gas. However, they require regular maintenance as they have a lot going on and if not maintained could leave you without backup power in a power outage.

Propane fuelled generators, otherwise known as liquid petroleum gas (LPG) generators, have the advantage that you don’t have to wait for the generator to cool before you refill, unlike diesel generators that require the tank to be cool before you refill them, meaning you’re able to run the generator continuously while keeping the propane topped up.

However, propane is less efficient than diesel and propane engines have a shorter lifespan, so if you’re looking to run your standby generator continuously, propane is probably not the best option.


How long can you run a diesel generator? A larger standby generator with a continual supply of diesel can run for about 500 hours before it’s recommended you allow it to cool and check it over. This is going to be your best option if you want to run a generator non-stop for extended periods.

Portable generators are not as suitable as they are limited by the size of their engine and fuel tanks, and other forms of fuel such as Liquid Petroleum Gas (LPG) are going to be more costly to run for prolonged periods.

If you would like help choosing the best generator for your needs, contact Solent Power today.

Paul Phelps Solar Power Owner
Paul Phelps
Paul is the MD of Solent Power and specialises in emergency power solutions, helping to protect your facilities from power loss. Get in touch with us today to discuss the different power brands that we can offer and how they can suit your needs.
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