How Much Fuel Does An Onan Generator Use? [Solved]

The lineup of Onan generators by Cummins Inc. is quite impressive. These models run on various fuels and have earned a strong reputation in the RV community and other enthusiasts. Still, it’s crucial to understand how much fuel they use to calculate your fuel costs and advance.

On average, Onan generators use 0.5 gallons of fuel per hour under moderate loads. That’s only an average figure, so some models use slightly more or less under the same conditions. High energy demands can drive that fuel usage up to a gallon per hour, while light usage can bring it down to approximately 0.2 gallons per hour instead.

This guide will help you understand Onan generators and their average fuel consumption. You’ll also discover a few tips on how to maximize your Onan generator’s fuel consumption to reduce your fuel costs and storage needs.

Let’s get started.

What Fuel Does Onan Generator Use?

Cummins Inc., the company that produces these generators, has models that use gasoline and LP (liquid or vapor) as fuels. 

Heavy-duty users with higher energy demand also have the option of choosing their diesel models instead.

With the Onan generator lineup consisting of various fuel types, you won’t have to worry about preparing alternative fuel tanks wherever you go. Instead, you can choose a generator that runs on the same fuel you’re already using for everything else.

How Much Fuel Does An Onan 4000 Generator Use?

The Onan 4000 generator consumes approximately 0.5 gallons of fuel per hour while under a moderate load. So, the generator will burn less fuel if it has no load, and it’ll burn much more if you’re placing a heavy demand on it.

That half-gallon rate of fuel usage is quite typical for Onan generators. You’ll find that most other Onan generator models use approximately the same amount, give or take 0.1 gallons of fuel per hour.

How Long Can An Onan Generator Run On A Gallon Of Gas?

An Onan generator can last between 1 and 2 hours on a gallon of gas. 

Of course, the exact duration will depend on which Onan generator model you have. Most models typically use only about 0.5 gallons of fuel per hour under a moderate load.

However, your generator will burn more gas if you place a higher load on it. For example, that’ll happen if you’re in an RV running power-hungry appliances like air-conditioning units.

On the other hand, a gallon of gas will last much longer if you only use your Onan generator for small appliances like phone chargers.

How Much Propane Does A 5500 Onan Generator Use?

Onan’s 5500 generator model uses 0.8 gallons of propane an hour under a moderate load (or ‘half-load’).

However, placing the generator under a full load will burn up 1.1 gallons of propane an hour instead.

How Much Fuel Does An Onan 7500 Generator Use?

The Onan 7500 generator is one of the brand’s diesel models. It uses an average of 0.49 gallons of diesel under a moderate load. Lighter loads will only consume 0.13 gallons per hour, though you can expect to burn 0.96 gallons every hour if you run the unit at full capacity.

How Can I Make My Onan Generator Consume Less Fuel?

As you’ve seen above. Onan generators come in all shapes and sizes. But, more importantly, you can find models that run on whatever fuel type you prefer.

Despite all those differences, you can follow a few common tips to ensure your unit uses fuel as efficiently as possible. Doing so will help you reduce your fuel costs in the long run.

Here are some ways you can make your Onan generator consume less fuel:

#1 Regular Maintenance And Servicing

Your top priority with an Onan generator should be regularly scheduled maintenance and service. That will maximize the unit’s overall lifespan, and it’ll also ensure it burns fuel efficiently.

Aside from regular maintenance, you should also service the generator whenever necessary. So, replacing any faulty parts will contribute to the generator’s overall efficiency, reducing its fuel usage.

#2 Maintain Correct Temperatures

Your generator is much like a standard car engine. That means it can only function optimally at the correct temperatures, neither too cold nor too hot. 

So, always ensure that your generator can cool itself efficiently, whether it uses air or water to do so.

#3 Never Underload or Overload

Believe it or not, underloading and overloading can increase your generator’s fuel consumption.

An overloaded generator will burn fuel too fast; that’s pretty clear. However, an underloaded generator will not reach its optimal temperature (similar to #2 above) and will work inefficiently.

In both cases, the Onan generator won’t burn fuel as efficiently as it should.

#4 Remove Carbon Deposits

As you continue using your Onan generator, carbon deposits will form as a natural byproduct. These deposits will form around parts like the generator’s piston tops, valves, and fuel injectors.

As you might imagine, these deposits will affect the generator’s fuel efficiency, causing it to burn more fuel than usual.

So, removing those deposits every year or so will maintain the generator’s efficiency and reduce its fuel usage.

How Long Do Onan Generators Last?

You can expect an Onan generator to last at least 10 years. However, that lifespan adds up to between 10,000 and 20,000 hours of total use for average users.

Naturally, your Onan generator will only enjoy a long lifespan if you take excellent care of it.

To do that, you must service your Onan generator regularly. Schedule and track your generator maintenance every 500 hours of use or once every two years, whichever comes first.

The maintenance tasks you must perform on your Onan generator during those service intervals include:

  • Changing the oil and flushing the coolant system
  • Replacing spark plugs, air filters, and fuel filters
  • Inspecting all parts, including fuel lines and batteries
  • Draining any condensation and water
  • And more, as instructed by the manufacturer in the generator’s user manual.

Remember: even if you don’t use your Onan generator often, you must still service the unit to maximize its lifespan. That will reduce its overall wear and tear while ensuring that it can produce power efficiently.

Still, let’s assume that you don’t take good care of your Onan generator. In that case, the unit will only last a fraction of its optimal lifespan. That could add up to 1,000 to 5,000 total hours of use, and you will not enjoy an optimal power output.

Final Thoughts

If you’re considering purchasing an onan generator, you’ll need to factor in the fuel it requires. While many onan generators use diesel or gasoline, there are also models that use propane.

According to Onan, an average generator will use 0.5 gallons of fuel per hour. That means if your generator runs for 8 hours, it will use up 4 gallons of fuel.

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