Best Oils for Generators

Oil is vital for the correct function of your generator. It acts as a lubricant for the moving components such as the camshaft and bearings inside the engine. This prevents the engine parts from corroding due to friction and helps to extend the lifespan of your generator.

 It also helps to transfer a small amount of heat away from the piston. 

The oil also acts as a protective barrier to the metal parts, preventing mineral deposits from building up.

Higher quality engine oils will also have detergents that will catch these mineral buildups and help to remove them through the filter.

This barrier also protects the metal from coming into contact with water and rusting.


Amazon Basics Full Synthetic Motor Oil - 5W-30 - 5 Quart

This is our top pick at $24.20 on For this money, you get a large 5 quarts of oil, meaning that you will not run out anytime soon! 

It is a 5W-30 oil and is designed to be used in gasoline engines. It is certified by the API (American Petroleum Institute).

The oil has safety ratings of API SN Plus, SN, SM, and SL. It is SAE certified and is rated ILSAC GF-5 or GF-4.

It is specially formulated to protect your engine components against friction and has been shown to help improve your fuel economy. 


  • 5-quart bottle
  • API Certified
  • ILSAC Certified
  • SAE Certified


Castrol GTX 10W-30 Conventional Motor Oil, 5 Quarts

Our next pick is the Castrol 03093 GTX oil at $16.97. This too is 5 quarts, making it cheaper than the AmazonBasics version. It is ranked lower due to having fewer safety certifications. 

This is a 10W-30 oil, meaning that it will not be as effective as the AmazonBasics oil at lower temperatures. 

The oil is designed for gasoline engines and is certified by the API and the SAE. It meets API SN, SM, SL, and SJ regulations.

It also complies with ILSAC GF-5, GF-4, and GF-3. It is formulated to protect against sludge buildup in the engine. 


  • 5-quart bottle
  • Cheaper
  • SAE Certified
  • API Certified



This is our next pick at $16.99 for 2 1 quart bottles. 

It is an SAE 10W-30 oil with a flash point of 392 degrees Fahrenheit. It is designed for use in a 4-stroke engine. 

This is a petroleum-based oil to increase the lubrication inside the engine. It contains shear-stable polymer additives combined with base stock. 

It meets API SM standards and exceeds the stated requirements. 


  • API Certified
  • SAE Certified
  • 10W-30


  • Only 2 quarts


Generac Full Synthetic Motor Oil 5W-30 SN Quart Bottle Part# 0J5140 (qt)

This is our most expensive pick at $29.79 for only 2 quarts, hence the low ranking. 

The fully synthetic oil is an SAE 5W-30 classification and is designed for use in gasoline engines.

It meets SAE standards, ILSAC GF-5, GF-4, and API SN, SN Plus, and previous API standards. This gives good confidence to the buyer that the oil is safe for use. 


  • 5W-30 oil
  • SAE Certified
  • ILSAC Certified
  • API Certified


  • Expensive for not much


Briggs & Stratton 100005 SAE 30W Engine Oil - 18 Oz

This is our cheapest pick at only $3.67, but will not give you as much oil. The bottle is roughly half a quart so is not best suited to running a large generator. 

It is an SAE 30W oil, designed for use in small 4-cycle engines. It holds up well to use at warmer temperatures.

The oil has been classified as SJ/CD by the API.


  • Very cheap
  • SAE Certified
  • API Certified


  • Very small bottle
  • Designed for use in small engines

Best Oils For Generators Buyer's Guide

Check What Your Manual Says

The easiest way to check the best oil for the optimal running of your generator is to check the owner’s manual. This will contain all of the information you need to know about your generator and should be your first port of call.

If you cannot find it, there are usually pdfs available for download online. Simply look for the model number and manufacturer’s name. Googling these will often give you the results you are looking for. 

Your owner’s manual will contain all of the information necessary to clean, maintain, and look after your generator. 

Types of Oil

There are 3 types of oil: real, full synthetic, and synthetic blend. Synthetic oil works better at higher temperatures than real oil as it does not increase in viscosity as it gets hotter. It is generally around 3x pricier but lasts longer than traditional crude oil. 

Synthetic oil can help your generator to use less fuel and will help to keep your generator’s motor in working condition. It also does not come with the environmental impacts of crude oil, so many people prefer it. 

Synthetic blend oil is a mix of completely synthetic and real oil. It shares a lot of the same properties as synthetic oil, but it is at a much lower cost. 


If you are buying a large quantity of oil, you may as well try and get one that can be used in multiple systems.

Not all oils are suitable for all motors, but it is worth checking.

We recommend purchasing a multi-functional oil where possible to save future you money!


If you are concerned about your environmental impact (let’s face it, who isn’t in 2020?) consider looking at how your oil burns. 

What is the operating temperature of your generator?

If you live in an extreme climate (hot or cold) you should take this into consideration when choosing an oil for your generator.

Different oils operate at different temperatures and are designed accordingly. Oil designed for use in -20 degrees Fahrenheit will not work well in a warm climate, and vice versa. 

Synthetic 5W-30 can be used in all temperatures and is a very versatile oil. Above 32 degrees Fahrenheit SAE 30 is likely the optimum oil to use. Between -10 and 40 degrees Fahrenheit, it is recommended you use 10W-30 oil. 

The Viscosity of the Oil (SAE rating)

Viscosity is a term used to describe the liquid’s resistance to flow - in other words, the internal friction of moving liquids. SAE stands for the Society of Automotive Engineers and is how motor oil viscosity is measured.

This will be indicated clearly in the name of the oil. There will be a letter W in the name, standing for winter. The number before the W is the viscosity at 0 degrees Fahrenheit. There will be a number after the W too, which indicates the viscosity at 212 degrees Fahrenheit. 

As a quick rule of thumb, the higher the number after the W, the better suited the oil is to higher operating temperatures. Oils with higher numbers are often thicker (more viscous) and adds lubrication to the engine components. 

Conversely, the lower the number before the W, the better suited the oil is to lower operating temperatures. For temperatures below zero degrees Fahrenheit, we suggest using SAE 5W-30. 

What Type of Engine is your Generator?

There are 2 main types of engine - 2-stroke and 4-stroke. To properly understand the difference you need to know what happens during a combustion cycle within the engine. 

There is a piston contained within the engine cylinder. During combustion, this moves up and down to the top dead center (TDC) and bottom dead center (BDC). TDC means that the piston is close to the valves, and BDC is when it is furthest from the valves. When the piston moves from TDC to BDC (or vice versa) this is known as a stroke. 

The entire process is known as a combustion cycle or revolution. When gas and air are sucked into the piston it moves down to allow the gases to collect in the combustion chamber.

The intake valve is forced closed as the piston moves up the cylinder again. This acts to compress the gas, which is then ignited through the use of a small spark. The piston then travels back up the cylinder and the exhaust valve opens to expel the fumes.

A 2-stroke engine requires just one piston stroke to complete the combustion cycle. They need fuel that has been pre-mixed with oil to work. There is an initial compression stroke followed by the compressed fuel explosion.

When the stroke reverses the exhaust fumes are expelled and new fuel is drawn into the cylinder. The spark plugs will only fire once per revolution and the power is generated once for every 2-strokes of the piston. 

Choose a Reputable Brand

For the best results, we suggest choosing an oil from a reputable source.

Common brands are Shell, Generac, Schaeffer, and Castrol. They should all come with an SAE rating clearly marked. 

Other indications of quality assurance are the API (American Petroleum Institute) logo and the rating SJ, SL, SM, and SN. 

Frequently Asked Questions

How Often Should I Change My Generator Oil?

Upon first use, we recommend changing the oil after only 20-30 hours. After this point, you should replace the oil after every 100 hours if using real oil. If you are putting synthetic oil in your generator engine, you can safely leave it in there for up to 200 hours. 

If your power is out for an extended period of time, this roughly equates to once every 8 days.  

This is because as it is exposed to heat, the oil begins to break down and this makes it less effective. It can even pick up small fragments of metal which can cause damage to the engine.

What Happens if I Add Too Much or Too Little Oil?

Neither scenario is optimal for the functionality of your generator.

If you do not have enough oil your generator will switch off prematurely and you are likely to activate the low-oil level warning system. If you continue to operate your generator past this point, it can cause the engine to burn. 

If you have excess oil in your generator then you can increase the resistance and potentially could have oil leaking through the air cleaner. 

How Much Oil Does My Generator Need?

This depends on how big your generator engine is.

As a rule of thumb, use these quantities as a guide.

80cc engine - 0.4 quarts

114-224cc engine - 0.6 quarts

270-459cc engine - 1.1 quarts

717cc engine - 1.4 quarts

754cc engine - 1.6 quarts

Can I Use Car Oil in My Generator?

Yes, you can. Most generators will require similar synthetic motor oils to the ones you use in your car.

This can help to save you money purchasing many different bottles of oil. 

Can I Use SAE 30 instead of 10w30 in My Generator?

It is not recommended by generator manufacturers, however, in practice, this does work.

We always suggest buying the correct oil for your generator according to the user manual. In a pinch though, this substitute will work. 

Why Do Generators Burn Oil?

There are a couple of reasons that generators could burn oil. These include the crankcase being overfilled or the wrong type of oil being added to your generator. If the air filter is clogged this could also cause your generator to begin burning oil.

Damage to the generator could also cause oil burning, particularly if the cylinder walls or piston rings are scored or damaged in any way. Clogged crankcase vent tubes, bad valve stem seals, and blown head gaskets can also be a root cause.

How do you Change the Oil in a Generator?

What Will You Need?

Personal protective equipment (goggles and gloves)

New engine oil

Drain oil can

Replacement oil filter

Clean brush and towel

Ratchet and oil filter wrench

Socket wrench

Phillips and flathead screwdriver

Funnel for oil

2 large, sturdy blocks

How do you do it?

Your first step is to start your generator and allow it to run for a few minutes to warm the old oil slightly. This will make it less viscous and easier to drain off. 

You should place the 2 blocks on a level surface and place your generator on the top. This will give you some space to work in, underneath the oil drainage plug. It is vital to place the blocks on a level surface to ensure the generator does not overbalance. 

Find the spark plug on your generator and unplug so that there is no chance your engine will start while you are changing the oil. If you are unsure where it is, check in your owner’s manual. Some manufacturers may even include more than one spark plug, so it is wise to check carefully.

Remove the wire connected to the spark plug. Hold the spark wire boot tightly, twist, and pull. This is a safe and effective way to disconnect the spark plug, no matter its quality. Do not try to pull the wire as this can quickly cause serious damage. 

Find the oil drain plug - this is usually a ⅜ inch nut with a hexagonal head. Wipe away any excess oil and grime and place the drain can underneath the hole. 

Remove the plus using the ratchet. Unscrew completely, being aware that oil will start draining as soon as you move the plug. 

Collect the oil in a container and set aside to dispose of it safely later. Loosen the oil filter with your wrench and manually unscrew. 

Using a small amount of oil, gently lubricate the gasket of the new oil filter. Start screwing in manually and finish off with a wrench. Do the same with the oil drain plug. 

Remove the oil fill cap and add your funnel to the hole. Slowly pour the oil into the generator. Remove the funnel and screw on the oil fill cap. 

Grasp the boot of the spark plug wire and press over the top of the plug until it goes all the way in. You will often hear a click when it is in the correct location. 

Turn your generator on and allow it to run for a few minutes, allowing the new oil to work its way through the engine.

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    I'm an environment and energy blogger who teaches outdoor and energy enthusiasts how to be better informed when it comes to purchasing or maintaining a generator, solar panel system, or anything else related to your energy needs.