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Best Generator Oils For Longevity

The lights start to flicker during the storm, but you don’t even notice. After all, you have a generator for backup.

image of oil pouring into funnel

But when was the last time your generator was maintained? You likely run your generator once every 3 months and are religious about using fuel additives for stabilizing the gasoline in the tank.

Does the oil type matter?

See Related: Choosing An Oil For Your Air Compressor

What Does Oil Do for a Generator?

While you can use standard car oil in the generator, your generator will have a different life than your vehicle.

If it is a standby generator, it may sit for long periods of time between use. If it is a portable generator, it may run for long periods of time after being transported and jostled.

Oil lubricates the camshaft and bearings and other rotating assembly parts inside the generator engine. This prevents early breakdown from friction. Oil also plays a small role in transferring heat away from the piston.

As oil is used, it begins to break down and become less effective. It also starts to carry small bits of worn metal.

This is why oil should be changed every 100 hours.

See Related: Top Side Creepers Improve Shop Effenciency

Quick Picks

Generac Full Synthetic Motor Oil5w-30Made by a generator manufacturer.
Briggs& Stratton Small Engine OIl5w-30Designed for Portable Generators.
Honda Motor OIl10w-30Designed for Long-lasting Honda engines.
Valvoline Full Synthetic0w-40Excellent brand with high protection.

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How to Choose the Right Oil for a Generator

Frankly, it’s hard to screw up the oil type. Generators are just happy to have oil. But if you are worried about getting the longest life possible, or you have some warranty concerns, this list will help.

blue generator

1. Read Your Manual

If you still have the manual, pull it out. Sometimes if you search for your model of the generator online with the words “pdf”, it will pull up a copy of the manual for you to reference.

Reference the section on generator maintenance to find the exact oil type. Generally speaking, most small engines will use 10w-30 oil with some of them switching to 5w-30 for cold weather and winter use.

2. Determine Your Engine Type

Most generators have a 4-stroke engine which requires the oil to be added separately from the gasoline. I’ve never seen a generator with a 2-stroke engine.

These 4-stroke engines work well on SAE 30 oil. Specifically, I recommend the 10w-30 which starts off thinner and thickens as the engine runs to provide greater protection.

3. Match Oil To Environmental Temperature

Guys who work on construction sites in the winter are very aware of how the temperature affects their equipment. In the hot summer weather above 110 degrees, you may want a thicker oil. 10w-30 is a good choice for temperatures up to 100+ degrees.

When the weather drops below 30 degrees, you need a thinner oil for better protection on cold starts. 5w-30 is excellent for winter temperatures down to -20 degrees.

4. What Is Viscosity?

You’ll see us frequently refer to viscosity or the thickness of the oil. The 1st number (such as 5w) refers to the thickness at 0 degrees Fahrenheit. The second number is the temperature above 212 degrees Fahrenheit.

The lower starting figure provides a thinner oil for better coverage when the engine is cold. As the engine heats up, the oil thickens to the second value, providing better protection under load.

Best Oils For Generators

The last time I needed backup power was the ice storm of 2007. The Extreme cold made it hard to keep the pipes from freezing. We used the generator to run several 1500 watt heaters inside and underneath the house.

image of red, black max portable 4500 watt generator

There are a lot of oils that are created explicitly for outdoor power tools. The same oils that you use in your leaf blowers or pressure washers should, technically, work.

However, Even those oils aren’t all built to the same standards. Here is a list of Generator oils that are held to a higher standard. 

1. Generac Full Synthetic 5W-30

generac oil

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This Generac oil is fully synthetic – this means that compared to conventional oil this one is extra distilled and modified. Generac adds some specific additives to this oil that is designed to protect their generators through long periods of sitting.

This large focus on quality means that this oil is considered a little pricier than others on the market. You more than get what you pay for though, as this oil works great in protecting against any sludge deposits while still maintaining proper viscosity in colder temperatures.

Generac generators are pretty much all propane or natural gas-powered since those fuel types don’t degrade over long periods of not being used. 

Definitely, I would highly recommend this type of oil for all kinds of Generac generators not only to ensure proper functioning but also to keep the warranty on the machine.

However, all generators face the same challenges that the Generac’s do, making this one of the top picks for This type of oil can work remarkably well in most of the continental United States as it holds its viscosity well even in extreme cold.

2. Briggs and Stratton SAE 5w30 Synthetic Small Engine

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Here’s another synthetic. In my own experience, and as I search forums for other homeowner’s use cases, synthetics consistently out-perform crude oils.

When it comes to small engines not many can compete with the raw experience of Briggs and Stratton – being in business for over a century means that this company knows everything on small engines. Their oil is specifically tailored to meet the demands of air-cooled 4-cycle engines, allowing you to keep your engine running smooth and well protected even under rigorous demands.

Each quart of Briggs and Stratton oil is protected with a high-quality detergent. This detergent is classified by the American Petroleum Institute as SJ/CD. This is a special designation that specifies this oil for air-cooled power equipment use. The largest national trade association with natural gas and petroleum certifies this product will work for just about any current generator out there today.

This type of oil is made explicitly for extremely cold temperatures.

The higher than average price turns off a lot of people to this product, but considering generator maintenance and oil changes are done only once every other year or so, then picking up this type of product is a no-brainer.

3. Honda Motor Oil 10W-30

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Best For High Use Construction Equipment. Honda is another company that is known for its quality products with everything mechanical. Their oil is no exception, either, as it has been shown to make motors run smoother and longer, especially with Honda generators.

This oil is also rated SJ by the API. This means that any 4-cycle engine made after 1996 should be compatible with this oil.

The viscosity rating means that this oil will work great for generators from equatorial to a temperate environment, but isn’t going to be as recommended for cold weather.

You are paying more for the synthetic price, which always scares a few folks. But for the contractor who relies on their generator daily, or is running a portable welder, light towers or other small engine-driven equipment.

It is also a good choice for homeowners choosing oil for standby generators in warmer environments.

This oil does a remarkable job in defending against varnish deposits along with maintaining viscosity year-round.

4. Valvoline Full Synthetic 0W-40 Small Engine

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This is one of my favorites for extreme cold weather use.

Being a fully synthetic small engine motor oil means that this Yamalube product will keep your engine cleaner longer.

Most importantly is that this synthetic is rated by the API at 0 weight (0W) viscosity which means it instantly flows to all parts of the engine within the first few cranks of starting.

This extremely low viscosity also has benefits in temperate climates. Even at room temperature, oil can start to thicken up, so when someone starts their generator, there is a lot of slow-moving crudes that has to work through the engine first before it warms up.

This means that your engine is not adequately protected for the first few minutes of use, creating problems with metal-on-metal performance.

This Yamalube oil has none of those problems, meaning that the damage done to your motor during startup is significantly reduced.

However, in my opinion, this product is the best for areas with extreme weather. You start at 0w for the quick coating properties and faster flow, but then it quickly moves to a 40 weight oil to improve protection under load and decrease oil consumption. (It is excellent for snowblowers)

It does not have the brand name recognition of the Generac oil, but it’s what I’m putting into my standby generator (technically, a portable generator that I use when the power goes out).

Rotella T6 5w-30 Synthetic Diesel Generator Oil

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There are a lot of great CJ-4 oil manufacturers, but one of my favorites is the Rotella brand. 

Rotella has a long history of keeping fleet trucks on the road, and I know vehicles that have been driven to the 1 million mile mark on Rotella oil.

The T6 offers added additives to reduce friction, and the 5 weight oil protects your generator under colder temperatures.

For the nerdy shopper who wants a better understanding of their engine, here is some insider information to help you make a more informed decision. Diesel Engines require a CJ-4 Designated oil from the American Petroleum Institute.

When I was a kid, I ran our riding mower dry of oil and seized the engine.

Dad dumped some Rotella down the spark plug hole and refilled it. After hand turning the engine a few times he got it going again and that mower ran another 2 years.

Ever since then, I’ve been a big fan of the Rotella for small engines.

Generators Oil Buyer’s Guide

For the nerdy shopper who wants a better understanding of their engine, here is some insider information to help you make a more informed decision. 

Can You Use Synthetic Oil In Generators?

Image of a home backup generator for use during power outages.

The short answer to this question is yes and is actually sometimes recommended. To fully understand why you first need to understand the differences between synthetic and conventional. Both types of oil initially come from the same place -the ground.

Synthetic differs as it goes through the higher process of refinement and distillation, with more chemicals added to modify and enhance the oils.

This process creates a cleaner oil that allows for a much higher level of protection along with increased performance, especially for smaller engines [1]. This has to do with overall superior viscosity in temperature extremes – synthetic oils lubricate better in frigid conditions or high-stress conditions that involve high temperatures and dust.

But for reliable backup power and longevity, these synthetics are hard to beat.

Plus, your generator’s maintenance routine maintenance schedule can be stretched out, requiring less downtime on power tool repairs.

How Often Should Generator Oil Changes Be Done?

Generator oil filters and oil filters should be changed every 100 hours of a generator running time. With Synthetic oil, that time can be doubled to 200 hours.

In a prolonged power outage, that is about once every eight days.

For comparison, most lawn mowers recommend changing the oil once every 50 hours.

When in doubt, remember: An engine has never been worn-out by too many oil changes.

As a quick side note, most lawnmower manufacturers recommend changing the oil filter and air filter once for every two oil changes.

How Does A Splash Oiling System Work?

image of man starting dirty generator on building site

The primary task of any oil system is making sure that all the moving parts are kept well protected by keeping it lubricated.

When it comes to air-cooled generators (and most outdoor power equipment) the principal way it keeps these parts lubricated is through a splash system. 

Splash oil systems are designed for shorter runs of 2 to 3 hours with a 30 minute cool down between (think 1 tank of gas). Many generators do run a pressurized oil system which work for longer runs. 

Inside the crankcase of the engine is a dipper that is driven by gears. This dipper grabs small bits of oil and flings it around the crankcase.

There are two separate ways it can do this – either through a connecting rod that picks up oil to spread around or through a spinning gear that splashes oil throughout the crankcase.

Either way, the end result is the same: Oil is distributed throughout the engine keeping it protected from dust and metal on metal damage [2].

Originally designed for use in steam engines, the splash oiling system is rarely used in water-cooled, 4-stroke, engines (such as those used in passenger cars), as the engine is too large for the oil to reach all of the needed areas. (Some bigger generators over 25 horsepower use an oil pump, too)

During prolonged outages, you should check oil levels daily. These splash systems used in air-cooled engines (most generators under 20kW) tend to burn more oil than a car would, and you want to make sure your oil consumption has not put the engine at danger.

Gas in Oil and Why You May Want a Manual Fuel Shut-Off for Your Generator

A weird quirk is that fuel can leak from the tank, past a stuck carburetor float, into the engine cylinder.

On worn engines or engines with stuck piston rings, the gas can leak past the cylinder on down below to the oil in the crankcase.

This dilutes the oil and causes the crankcase to overflow with a diluted gas and oil mixture.

The symptoms of this are a non-start engine. Repeated tries to start the engine can lead to engine failure (although, in my experience, this rarely happens).

The last thing you want to do in a power outage is to have to change your generator’s oil.

Fuel shutoffs are little knobs inserted into the fuel line to turn off the flow of fuel to the engine. They can easily be added to most high-end generators in about 30 minutes of work.

If your engine does not allow for a fuel shut off, it makes sense to keep the gas tank empty until it needs to be used.


Our readers submit questions to us. I try to find answers and add them to this post.

What is the best oil to use in my Warrior Diesel generator?

SAE15w40 diesel engine oil. It is recommended to change after the first 20 hours, then after every 100 hours following.

Can I use Synthetic Oil in My Gas Generator?

Absolutely! Synthetic oil is more refined and “slippery”, and can — theoretically —  provide a better coating. However, there does not appear to be any indication that synthetic oils extend the lifespan of these small, air-cooled, motors.  Any benefit from synthetic is likely limited to motors with overhead valves (OHV).

There is always some confusion about the safety of synthetics, as some of the earlier small engines struggled to perform and suffered from overheating problems when synthetics were first introduced.

These days, synthetics are ubiquitous and manufacturers build their machines to be compatible. Even on small generators, synthetics are ok.

Keep in mind that while synthetic oil can lengthen the distance between oil changes in a car, you should still change your  See Briggs and Stratton, Honda, and Cummins Onan

Can I Use Synthetic Diesel Oil In My Gasoline Engine?

As a kid, we just used dad’s diesel oil in all of our mowers and generators and other power tools. He bought the it in bulk, and it seemed to work well.

The good news with Diesel oil is that it is engineered for higher wear. So it will contain a higher level of zinc dialkyldithiophosphate and other surfactants. These are excellent for a diesel engine, and many semi-trucks see over a million miles before an engine has to be rebuilt.

So why don’t all cars use Diesel oil? Some of that may have to do with the EPA. The catalytic converters on the modern automobile would be clogged by the zinc by-products that make it into the exhaust. Diesel motors are “dirtier” and have systems that allow for this problem.

Your gasoline generator will likely not have a catalytic converter to get in the way so you could theoretically argue that it might work. However, I’m not an engineer, so I’ll just leave you with this information and let you make your own decision!

Can I use a different brand oil than my generator’s motor?

Absolutely. Most generators do not manufacturer their own oil, and simply provide a recommendation as to the viscosity of oil to use. You can use any reliable brand of oil with that matching viscosity.

Conclusion | Best Oil

This article has been geared for homeowners with standby generators. Low viscosity synthetic small engine motor oil is your best bet for reliable protection.

For high daily use generators (such as construction site generator engines), a 10W-30 Synthetic oil provides all-day protection with less consumption and fewer oil changes.

At a minimum, change the oil and oil filters once a year, even if the generator has not been used much.


Zachary Drumm

Hey! My name is Zachary Drumm! This site allows me to test new tools, piddle around in the garage, and share the insights I get from flipping cars and houses. When it comes to tools, home improvement, and being a “shade tree mechanic,” you’ve come to the right spot. If I’m not in the garage creating content, you’ll find me outside, running, canoeing, and traveling. My goal is to empower more people to be self-sufficient.