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What Kind of Oil Does a Generator Use? – Detailed Guide

Written by Jamie Masterson

If your generator engine is running at a temp above the freezing point of water (32°F), use an SAE 30 oil. In case the operating temp gets Below 40°F and down to -10°F, a 10W-30 oil will work the best. Get a synthetic 5W-30 oil for all-purpose use.

oil for a generator

Types of Generator Oils

Conventional oil

The oil, primarily known as engine oil, is used to protect the part of the engine from excessive heat and friction. Generators use the same motor oil as your car. Earlier units used conventional oils mainly, but the practice is not so common today.

Conventional or regular oils are produced from natural crude oil. They offer a decent amount of protection, but can’t outperform synthetic oils. They are easier to find, cheaper, and less refined than their synthetic counterparts.

Conventional oil

Conventional oils usually don’t have any added quality modifiers (additives) in them, so they only offer a decent amount of protection.

Synthetic oil

Synthetic oils use a conventional oil base, refine it, and incorporate a wide variety of additives for improved performance. Unlike conventional oils, synthetic oils can perform in a wider spectrum of temperatures, protect your engine better, and keep your engine cleaner.

Due to the complex manufacturing process and the number of additives used, synthetic oils are more expensive and modern-day generators mostly depend on them.

Synthetic oil

Synthetic oils are designed to last longer, provide a wider range of functionalities, and keep your engine healthier. Some of the additives used in synthetic oils include detergent, defrosting agent, anti-bubble agent, anti-corrosion agents, and many more.

Standard Oil vs Synthetic Oil: Which One to Choose?

If you have a newer model of generator, synthetic oils will probably be the best option for you. This might be true that standard oils also protect your engine, but they do much more than just provide lubrication.

For an older model of generator, find out the best oils to use in the user manual. Each generator comes with a user manual that clearly mentions which oils to use and how.

This method also applies to newer generator models. Synthetic oils won’t be able to provide much support to the older models.

Standard oil vs synthetic oil

Synthetic oils contain much more additives than regular oils, which makes them exponentially more efficient in providing lubrication, dissipating the heat, and cleaning the engine. Nowadays a typical motor oil contains additives up to 30%.

Let’s look at some of the most commonly used additives in synthetic oils:

Additive Type Example Effect
Antioxidants Zinc dithiophosphate Prevents oxidation
Anti-foaming agents Silicone polymers Prevents bubble forming in the oil
Pour point depressants Alkylated naphthalene Modifies the oil’s properties in lower temperature
Anti-wear agents Stearic acid Reduces wear and tear
Friction modifiers Organic fatty acids Reduces friction and heat
Extreme pressure (EP) additives Sulfurized mineral oils Minimize adhesive wear
Viscosity index modifiers Alkylated styrenes Controls the viscosity of the oil
Rust and Corrosion inhibitors Basic metal sulfonates Prevents rust and corrosion
Detergents and dispersants Polymeric alkylthio-phosphonates Brakes down and cleans build up deposits
Demulsifiers Silicone polyethers Helps the solution to mix with other additives better

When it comes to choosing the right oils for your generator, always follow the user manual. Each manufacturer produces engine oil slightly differently. Consult a professional if you don’t have access to the information on your user manual.

Oils Used in Different Types of Generators

Diesel generator

Diesel generator

If you want to find the perfect companion for your diesel generator, there is no other option but to go through your user manual. You can only use outside oils if that grade/rating matches the operating temperature range of your machine.

We recommend using a thinner oil like 5W-30 in the cold temperatures and a 10W-40 in the hot summer seasons. Contact an expert if you need professional opinions.

Gasoline generator

Gasoline generator

If you’re looking for the perfect oils for your gasoline generator that can be used all year round, we recommend a versatile option like the 5W-30. In case the operating temperature of your machine gets above 32°F, use the SAE 30 oil.

On the flip side, if the engine temperature is below 40°F and down to -10°F, an oil with a 10W-30 rating will perform better.

Propane/NG generator

Propane generator

Generators that use propane or natural gas provide a cleaner burning process. Cleaner burn means higher temperature and that can cause more viscosity breakdown. That’s why they require specially designed engine oils.

Specially designed engine oils (Ex: 15W-40) will work better at higher temperatures and provide fewer viscosity breakdowns.

What Do the Numbers on the Bottle Mean

What do the numbers on the bottle mean

Every synthetic, multigrade oil bottle is marked with some rankings to showcase the range of working temperature and viscosity. The number looks something like this: 10W-40.

Here, the first number is equipped with the letter “W”, which refers to the winter season or cold temperature. The number shows the viscosity grade of that particular oil at different temperatures.

The 1st part indicates the starting temp of the engine and the 2nd part refers to the operating temperature.

The first half of the ranking also shows the viscosity grade of that oil at the starting temperature of your engine (32°F). 10W means the liquid acts like a 10-grade viscous liquid at 32°F. The later part of the ranking shows the viscosity grade at the operating temperature (212°F).

Note that the viscosity of the oil won’t change physically, rather the oil would act like a more/less viscous liquid at that specific temperature. A 10W-40 ranking means that the oil will act like a 10-grade viscous liquid at 32°F and like a 40-grade viscous liquid at 212°F or higher.

What do the numbers on the bottle mean

Tips to Choose the Right Generator Oil

Follow the manual

We can’t stress this enough. As I’ve mentioned earlier, every manufacturer has a slightly different formula when it comes to engine oils. Also, your generator’s manufacturer knows exactly what oil you should use. That’s why going through your user manual is so important.

Follow the manual

Check the viscosity

This is another crucial factor for choosing the right oils for your generator. You’ll need to buy your engine oils according to your engine’s temperature. Most generators can work with an SAE 10W-30 oil type. However, you should follow the instruction manual of your machine.

Check the viscosity

Find the operating temperature

Not all engines will operate at the same temperature. Depending on your weather, you may need to run your engine at a higher or lower temperature than usual. That’s why it’s important to keep the operating temperature in mind. Here is a general guideline.

  1. If you run your generator above 32°F (0°C) — use an SAE 30 oil
  2. If the temperature stays between 40°F (4.4°C) to -10°F (-23°C) — a 10W-30 oil will be better
  3. For all-purpose uses — a synthetic 5W-3 oil will do

Engine type matters too

Different types of engines work at different temperature ranges. That’s why what is good for a diesel engine might not be the best choice for a gasoline engine. For example, a 2-stroke engine uses fuel and engine together whereas a 4-stroke engine uses them separately.

Buy from reliable sources

Cheaper, low-quality oils may cost you some money in the short term, but it will set you even further back in the long run. Lower-grade or counterfeit oils may damage your engine, which will send you down a path of costly repairs/replacements.

Buy from reliable sources

Some trusted and leading oil brands in the USA include:

  • Honda
  • Motor 1
  • Shell Rotella
  • Briggs & Stratton
  • Generac

How to Change Generator Oil

This is how you can change the engine oil of your generator effortlessly:


Q. When should I change my generator oil?

The general recommendation to change your generator oil is after every 100 hours of operation. If you use your generator less frequently, the oil can last up to 150 hours. However, it’s strongly recommended that you follow the instructions provided in your user manual.

Q. What happens if I put the wrong oil in my generator?

Using the wrong oil in your generator can be devastating. Your engine parts may wear out before time, which can end up in permanent engine damage, or if not treated, can result in a complete engine failure.

Q. Are SAE 30 and 10W-30 the same?

Not at all. Unlike the 10W-30, the SAE 30 oil can not work efficiently in lower temperatures. It is optimized to work better at higher temperatures. The 10W-30 on the other hand will work like a 30-grade viscous oil at the operating temp and like a 10-grade oil at a lower temp.

Q. How many quarts of oil does a generator take?

Depending on the size, a standard generator can hold 1.1 to 1.9 quarts (1- 8.5 liter) of engine oil.

About the author

Jamie Masterson

With decade-long experience as a generator technician, Jamie has worked with USA’s top generator manufacturers and suppliers as an independent contractor.

The long years of service to the industry has taught Jamie the ins and outs of troubleshooting, repairing, and maintaining all kinds of generators in home, industrial and outdoor settings.

Jamie thinks this platform is a great opportunity to share his tips and tricks with you so you can make the most of such power equipment for better living.

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