What type of engine oil should be used in a generator?

Engine oil is used to lubricate the moving parts, cool and clean the engine, protect against corrosion, and enhance the sealing of the engine. It is important to highlight that all generators are not the same and may need a different oil.

Today we will discuss what type of engine oil you should use in a generator. What are the associated risks, benefits, and disadvantages of not changing/changing engine oil at the right time? A majority of your questions related to engine oil will be answered after reading this article. So, hang on with us while we take you on an interesting and informative ride.

What type of engine oil should be used in a generator?

Before deciding what type of engine oil is best for your generator, you need to consider some points. Wrong oil can cause serious troubles for your generator. Therefore you must carefully select the engine oil. Let’s look at the factors/checklist before selecting your generator’s engine oil.

Go through the User Manual

It is important to go through the user manual before buying oil for your generator. The user manuals have complete information on what type of oil is best for engine oil and under what conditions. Some companies also list the recommended oil brands that are best for the respective generator. We suggest you go with the recommended ones. They may be a bit costly but will enhance your generator’s performance and overall life.

Type of Engine

You will be surprised to know that there are some 2-stroke generators still available in the market. A lot of old people still have 2-stroke generators with them in mint condition. Many engine junkies keep a 2-stroke generator because they are fond of it. If you have a 2-stroke engine, we are pretty sure that you already know which is the best oil for your generator. However, you can also find the best ones here. 2-stroke engines use a combination of gasoline and engine oil. The mixing instructions are mentioned on the oil packaging and in the user manual.

The other and most common type of engine found in portable or standby generators is a 4-stroke engine. The size and classification of the engine vary from one generator to another, but all the 4-stroke engines use the same type of oil, known as SAE 30. SAE stands for Society of Automotive Engineers. It is a US-based, globally active association of engineers and provides standards for rating various things in the automotive industry such as horsepower ratings, aerospace industry standards, level of autonomy, and viscosity rating for engine oils. “30” in SAE 30 means the viscosity of the oil. It is commonly used for, generators, lawnmowers, and other engine-based power tools. There are a couple of variations of SAE 30, such as SAE 5W-30 and SAE 10W-30. Each of these variations has different properties which are suitable for different working conditions. We will discuss this in more detail in the next sections.

Oil Viscosity

Oil viscosity is one of the most important factors when selecting the right oil. As already discussed, the best way to select the oil is to follow the manufacturer’s directions.

Oil viscosity is the measure of how well the oil can pour at a specific temperature. Thinner oils have a low viscosity and pour more easily at lower temperatures than thicker oils with a higher viscosity. Thin oils reduce friction in the engine and help the engine start quickly during extremely cold weather. For example, in the oil SAE 10W-30, 10W means how well the oil can be pumped at lower temperatures. 5W has better pumping in cold weather than 10W. Please keep in mind that W here means winter and is not related to the weight or volume of the oil. The second number in the name, “30”, means how well the oil can be pumped at 212 Fahrenheit (100 C).

A common generator user doesn’t need to know this information. You can buy the oil by simply checking the recommendations. However, when the machine grows old, and the engine’s power decreases, the right type of oil can make the machine perform better according to the working conditions.

Operating Temperatures

The operating temperature is the most important factor when selecting engine oil for a generator. We have gone through hundreds of manuals, and each of them has pointed out that the user must consider the operating temperature before buying the generator oil.

Generac, one of the best generator brands in the North American market, suggests using engine oil according to the operating temperature. Once you know which oil is best for your area, making the right call will be easy. Let’s check out Generac’s recommendations.

  • Above 32°F: SAE 30
  • Below 40°F and down to -10°F: 10W-30
  • For all temperatures: Synthetic 5W-30

When you are not sure which oil is best according to the temperature, go with 5W-30 and let go of all the worries.

Best Generator Oils

Now that we have discussed in detail how to select the right oil for your generator, it is now time to look at some of the best oils currently available on the market. These oils have hundreds and thousands of reviews from satisfied customers and are recommended by various generator brands. However, we suggest you check the user manual before picking the right oil for your machine.

Types of Generator and Engine Oil

The type of fuel on which the engine runs is also very important. You can’t use the same oil in a gasoline engine and a diesel engine. Hence, if you have a diesel generator, all the other factors discussed above will remain the same, but you will buy a diesel variant of the same oil. Diesel variants are easily available online and in stores nearby. Similarly, if you have a natural gas generator, you will be going for the natural gas variant.

Advantages of Timely Oil Change

Just like an automotive engine, there are hundreds of moving parts in a generator’s engine. Engine oil is compulsory to keep them going without friction. Following are the key roles/benefits of engine oil. We will also explain how a timely oil change enables you to get more out of your generator.


It is the main role of engine oil. The pistons in the engine are continuously moving, and there is a lot of friction between them. Engine oil reduces this friction and provides a layer of oil for frictionless movement. When oil’s life is over, it loses its ability to lubricate. Therefore a timely oil change ensures lubrication and provides a friction-free environment for pistons.


Engine oil keeps the engine cool. When electricity is produced from the generator, a lot of heat energy is also produced as a by-product. Moving engine oil removes the heat from the pistons and keeps them cool.

Protection from Corrosion

Engine oil helps slow down corrosion on the metallic parts of the engine. The oil gets oxidized by coming in contact with oxygen and loses its protection ability once the recommended running hours are complete. Hence, you must change the oil timely to protect your engine.


One of the most important functions/benefits of engine oil is to clean the pistons. Microscopic sediments and dust particles gather over pistons from time to time. Engine oil comes in contact with pistons and removes these particles. The oil then carries these particles to the oil filter, where they are captured.

Longer Lifespan for Engine

All the benefits discussed above lead to a longer lifespan of the engine. When the friction is reduced, corrosion minimized, and the engine is kept cool and clean, it increases the engine’s durability.

Better Performance

Engine oil ensures better performance. Less friction leads to stable output production.

Better Fuel Average

Overused engine oil or low levels of engine oil results in poor fuel averages. It happens due to increased friction and decreased engine efficiency. As a result, the engine consumes more fuel to produce electricity. Hence, it is vital to ensure optimum oil levels and replace the engine oil timely.

Risks/Disadvantages of not changing the Engine Oil on Time

We have listed the benefits of a timely oil change. If you don’t replace the engine oil or run your generator with low oil levels, the following problems can occur.

  • High fuel consumption rate
  • Overheating
  • Fluctuations in the output
  • Decreased engine life
  • Higher running sounds
  • Increased CO2 emissions
  • Jamming and grinding of engine parts


Let’s look at some of the FAQs related to engine oil and its replacement.

How to check the oil level in my generator?

Standby generators display the oil level and give warning signs when the engine oil gets below the recommended level. Some portable generators also have this feature. Modern-day machines won’t start if there is not enough oil in the engine. If your generator doesn’t have these features, you will have to manually check the oil levels in the machine.

To manually check the oil level in your generator, let it sit for 5-10 minutes after turning off the unit. Locate the dipstick on the generator. If you don’t know where it is located, refer to the product manual. It is usually located on the engine side of the machine. Once you have located the dipstick, take it out, wipe it with a clean cloth and insert it back. Now remove the dipstick again and check the immersed side. The dipstick usually has the letters “F” or “L” written on it. F stands for full, and L stands for low. If the oil level is in between the two marks, then you don’t need to worry. If the oil level is below L or very near to it, you need to add engine oil. Please keep in mind that continuously decreased oil levels indicate a problem with the engine and you must consult a professional or claim warranty (if available).

How much oil will my generator consume?

There is no standard amount of oil that your generator will consume. As long as you check the oil level and replace the oil timely, you don’t need to worry about it.

How often should engine oil be changed?

The oil change needs of a standby generator are different from that of a portable generator. The general rule is to change the engine oil after the first 20-30 hours of operation and then every 100 hours. Some high-quality oils have more life. You must consider the manufacturer’s guidelines, oil packaging instructions and consult customer service for the best plan of action.

How to change the engine oil in my portable generator?

oil changing process in a generator

To change the engine oil, you will need the following things

  • New oil and oil filter
  • Canister/can for oil drainage
  • Gloves and goggles
  • Clean brush and towel
  • Oil funnel
  • Generator tool kit

Follow the directions below for changing the oil

  • Clean the area around the oil dipstick and oil cap.
  • Heat the old oil by running your generator for 5-10 minutes. If your engine has low oil, you will need to drain the oil by tilting the generator.
  • Raise your generator by placing it on concrete blocks/bricks. You may need help if you have a heavy unit.
  • Remove the spark plug.
  • Place the canister under the oil filter and remove the oil plug.
  • Replace the old filter and tighten it securely.
  • Pour new oil.
  • Reconnect the spark plug and check the oil levels.
  • Run your generator for 5-10 minutes to ensure everything is in order.

For standby generators, refer to the instruction manual or get the oil changed by a professional.

Why is there gas in my generator oil?

Gas in engine oil occurs due to a couple of reasons. Either the fuel shut-off valve is not closed properly, or the fuel float in the carburetor is stuck in the open position due to stale fuel or debris deposits. You can eliminate these problems by closing the fuel shut-off valve when the machine is not in use. If the problem persists, it is probably due to a faulty carburetor. Get your carburetor serviced in this case. A detailed guide for cleaning the carburetor is given here. If you still can’t find the issue, it is time to get in touch with professionals.

How to bypass the low oil sensor on the generator?

low oil pressure sensor

Bypassing the low oil sensor on the generator is an easy process. You need to remove the wire from the low-oil pressure switch and tape it so that it doesn’t touch the ground. Though it is not recommended to bypass an oil sensor, sometimes you need power more than anything and even more than the risk of creating potential problems for your generator. Once the purpose of running the generator is fulfilled, attach the wire back and refill the oil in your generator.

What happens if the oil level is too low?

Too little oil will give a very low runtime. It will overheat the unit and can cause engine problems.

Final Words

We are sure that generator maintenance will now be easier for you. A timely oil change can save hundreds of bucks and keep your valuable machine going for a long time.

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