What Kind of Oil Does a Generator Use?

Generators are motors that convert mechanical energy into electrical energy. 

These units need oil to lubricate their moving parts and run smoothly. Generator oil also cools down your unit and prevents corrosion or rusting, extending its lifespan. 

You can use different oil types in generators. Single-grade, Multigrade, and Synthetic are the most common types in retail outlets and online stores.

Understanding their differences will help you choose the right one for optimal performance. Here’s everything to know about generator oil.

What Kind of Oil Does a Generator Use?

There are three different oil types for generators: 

  • Single-grade
  • Multigrade
  • Synthetic

These lubricants are graded based on viscosity or thickness. Single-grade oils have a lower viscosity level, while multigrade types have an enhancer known as a Viscosity Index Improver, which keeps them from thinning out as they heat up. 

Synthetic variants blend chemicals into crude oil and are not as affected by temperature changes as others.

Which Oil is Best for Generators? 


  • Synthetic oil has a higher viscosity, meaning it is thicker and can better withstand high temperatures. 
  • They do not break down as quickly and last longer than other types. 
  • Plus, it has a few contaminants hence less clogging.

However, synthetic oil is more expensive than single-grade and multigrade. 

Single-grade & Multigrade

  • Single-grade types are the least dense, meaning they are thinnest and can’t withstand high temperatures as well. 
  • Multigrade tries to enhance thickness with enhancers, but it’s still less dense than synthetic.

However, both conventional oils are less expensive than synthetic oil. 

So which is the best oil?

Synthetic oil is best for generators because it can withstand high temperatures and lasts longer. It’s also the better choice because it does not clog filters.

But synthetic is no one-size-fits-all! Remember, what’s best for one unit may not fit another– as we’ll discuss in a few.

Understanding Oil Gradings for Generators

The Society of Automotive Engineers (SAE) has a system for grading and ranking oil based on viscosity. Many automakers and generator companies use it to determine the best lubricant for a particular engine. 

The SAE system has five grades: 0, 5, 10, 15, and 20. These grades are based on the oil’s viscosity at low temperatures. The higher the grade, the more the thickness and the better it performs.

  • SAE 5W-20 works best from -37⁰ to 77⁰ F
  • SAE 5W-30 performs best from -22⁰ to 86⁰F
  • SAE 10W-30 works between -20⁰ and 96⁰ F
  • SAE 10W-40 performs best from -15⁰ to 100⁰ F
  • SAE 15W-30 works optimally from -13⁰ to 95⁰ F

Remember, the SAE system uses several different classifications for oils, depending on their intended use.

Why You Should Follow Your Generator Maker’s Recommendation

If your manufacturer recommends an SAE or specific oil brand, it’s advisable to follow their advice. 

This is crucial because the maker understands what’s best for your unit. Such oil is formulated to protect your generator and keep it running smoothly. Checking the SAE rating is the best way to ensure you use the right product for your generator.

Remember, using the wrong oil can damage your backup. Even worse, it can void your warranty if the machine breaks down within the guarantee period.

What Happens if Oil Level Runs Low?

Oil lubricates all moving parts and keeps your generator cool. A few things may happen if the level drops:

  • First, the oil may only reach some of the parts that need lubrication to run properly. This can cause the generator to run rough and make noise. 
  • The unit may require more work to start.
  • The generator may start to overheat and catch fire.
  • It may also produce metal-on-metal noises due to a lack of lubrication.

Finally, low oil levels can cause the generator to seize up, which can be dangerous. 

How to Inspect Oil Levels

You can tell if your generator needs an oil swap by checking the level and color. The lubricant level should be;

  • at the top of the dipstick
  • light in color 
  • free of debris

If it’s dark, way below the dipstick line and dirty, you need an oil change.

Knowing how to check and change the oil on your generator is essential to keeping it in good shape. By taking these simple steps, you can prevent your generator from breaking down and costing you money.

How Much Oil Does a Generator Need?

The amount of oil a generator needs depends on its size, but it typically ranges from 2 to 4 liters. 

After refilling, use the dipstick to track the level and confirm that you have added the correct amount. 

If you run your generator for extended periods, check the oil level every few weeks. Remember, deficient levels can damage your backup power source.

How to Change the Oil in a Generator

The process is simple if you need to exchange the oil in your generator.  

  • First, consult your generator’s manual to find the recommended type, viscosity, and amount your unit holds. 
  • After that, shut down your backup and let it cool down for around 20 minutes. 
  • Next, loosen the drain plug and drain the used lubricant into a container.
  • Once you’ve drained out everything, replace the drain plug and fill the generator with a new bottle. 
  • You can use the dipstick to check the level and add more if necessary. 

Finally, start the generator and run it for a few minutes to ensure everything is working correctly.

How Often Should I Change Generator Oil?

The frequency of oil swaps will vary depending on how often you use your generator and other factors, including:

  • The make and model of the generator, 
  • The lubricant used
  • Manufacturer’s recommended lifespan
  • The environment where you run your unit (does it make your oil dirty?)

If you only use it occasionally, you can probably get away with changing the oil once a year. 

If you use it regularly, you should change the oil every three months or 200 hours, whichever comes first.

Can I Use My Auto Oil in My Generator?

Yes, you can. Automotive engines typically use 5W-30 or 10W-30 oil, the recommended SAE for most generators. 

Either of these variants should work fine in your unit. Also, mixing the two oils may provide better performance.

What are Some Popular Generator Oil Brands?

There are many reputable generator oil brands on the market, each with its advantages. For example, Castrol is known for its high-quality products and range of options, while Shell is known for its eco-friendly products. 

Some of the most popular brands include

  • Shell 
  • Castrol
  • Honda
  • Valvoline
  • Chevron 
  • Mobil 

These brands all have a long history of providing high-end products that meet different customers’ needs. 

For example, the Shell Rotella T6 Full Synthetic Diesel Engine Oil is designed to offer exceptional wear protection and cleanliness. It also has excellent low-temperature properties, making it ideal for cold-weather operation. 

If you own a Honda, try the Honda Genuine 5W-30 Engine Oil, specially formulated for their generators. On top of excellent protection against wear and deposits, it has a low volatility rate, meaning less oil burn-off.

Alternatively, try the Valvoline Premium Blue Extreme 5W-40 Diesel Engine Oil. This product offers excellent protection against deposits and has outstanding low-temperature performance. Plus, it’s compatible with after-treatment devices.

What to Look For in the Best Generator Oil Brands

When choosing generator oil brands, there are several things to keep in mind:

The type of engine you have

Depending on your unit’s engine, you may need to use different oil types. For example, four-stroke engines require conventional oil, while two-stroke engines may require synthetic or semi-synthetic oil.

Your climate and operating conditions

The climate you operate your generator in and how often you use it will also affect your choice of oil type. You may need synthetic or semi-synthetic variants if you live in a hot or high-altitude area.


Some oil additives can improve the performance of your generator’s engine. However, not all additives are compatible with all engine types. Check your owner’s manual before adding any additives to your lubricant.

Change interval

You can extend the interval between swaps depending on the brand/type of oil you use. However, always check your owner’s manual for the OEM interval for your specific model.

Final Thoughts

Generator oil is crucial in maintaining your backup power source and keeping it running smoothly. 

It helps to understand the following if you have a unit:

  1. The right oil type for your generator
  2. How to drain out old oil and replace it with a new bottle
  3. How much oil your unit needs
  4. The correct oil change interval

Lastly, when choosing a generator oil brand, always consider the engine type, climate, operating conditions, maker’s OEM, and oil change interval.


Can I use synthetic oil in my generator?

  • Yes, you can use synthetic oil in your generator. 

How often should I change the oil in my generator?

  • You should change the oil in your generator every 3 months or 200 hours of use, whichever comes first. 

What are the consequences of not changing the oil in my generator?

  • If you do not change the oil in your generator, it may overheat and be damaged. 

How do I dispose of used generator oil?

  • Used generator oil can be disposed of by taking it to a local recycling center.
What Kind of Oil Does a Generator Use?

Carter Brooks

I'm Carter Brooks, an expert in portable generators with a background in Mechanical Engineering. My experience spans from working in the manufacturing industry, where I gained hands-on knowledge of various machinery, to a focused career in blogging about portable generators. I combine my technical expertise with real-world experience, garnered from numerous camping trips and outdoor adventures, to provide in-depth reviews and practical advice. My blog is dedicated to helping consumers understand and choose the best generators for their needs, emphasizing both efficiency and environmental impact.

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