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10 Best Oils for Generators of 2024 – Reviews & Top Picks

Best Oil for Generaor

close up AmazonBasics AM0D533Q Full Synthetic Motor Oil

Whether you rely on your generator only occasionally to keep the lights on when the power’s out or use it daily in your RV setup, your generator’s needs are the same. It requires regular oil changes with high-quality oil to reduce friction and keep your generator running. A failure could mean no generator when it’s needed most.

We want to ensure you’re never left in the dark due to wear and tear or picking the wrong product, so we decided to determine exactly which oils could be trusted to power generators. To do so, we tested several brands of oil, comparing our findings in the following 10 reviews.

A Quick Comparison of Our Favorites

Rating Image Product Details
Best Overall
Castrol 03129C EDGE High Mileage Motor Oil Castrol 03129C EDGE High Mileage Motor Oil
  • Extra fluid titanium technology ,Increased fuel economy ,30% greater oil film strength
  • Best Value
    Second place
    AmazonBasics AM0D533Q Full Synthetic Motor Oil AmazonBasics AM0D533Q Full Synthetic Motor Oil
  • Fully synthetic ,Resists thermal breakdown ,Reduces exhaust emissions
  • Premium Choice
    Third place
    Generac 0J5140 Full Synthetic Motor Oil Generac 0J5140 Full Synthetic Motor Oil
  • Superior viscosity breakdown protection ,Synthetic base with additional additives,Prevents sludge and varnish deposits
  • STP 18589 4 Cycle Oil Formula STP 18589 4 Cycle Oil Formula
  • Made specifically for small engines ,Controls engine oil viscosity ,Creates a protective layer at high temps
  • Cummins 3265336 Onan SAE 15W-40 Oil Cummins 3265336 Onan SAE 15W-40 Oil
  • Perfect for Onan generators ,Pack of 4 ,Maximum protection formula
  • The 10 Best Oils for Generators – Reviews 2024

    1. Castrol 03129C EDGE High Mileage Motor Oil – Best Overall

    Castrol 03129C EDGE High Mileage Motor Oil

    Castrol EDGE high mileage motor oil is made to keep high-mileage vehicles running longer, so it stands to reason that it would be a great choice to keep your generator running longer. However, there are more benefits than just an improved lifespan. Castrol EDGE features extra fluid titanium technology, which increases oil film strength up to 30% while reducing its breakdown.

    When using Castrol EDGE, you can expect increased fuel economy. Since it’s a fully synthetic formula, you won’t have to change it as often as non-synthetic oils. And this formula is also made to be 10 times stronger against high-temperature oil thickening.

    Granted, this oil is not made specifically for small engines like some of the other options on this list, but that means it’s also much more affordable. And if it can be trusted with our vehicles, there’s no reason we can’t trust it in our generators as well. Overall, Castrol EDGE is the best overall oil for generators we reviewed this year.

    • Extra fluid titanium technology
    • Increased fuel economy
    • 30% greater oil film strength
    • 10 times stronger against high-temp oil thickening
    • Fully synthetic formula
    • Not made specifically for small engines

    2. AmazonBasics AM0D533Q Full Synthetic Motor Oil – Best Value

    AmazonBasics AM0D533Q Full Synthetic Motor Oil

    Generators are already expensive, but maintaining one doesn’t have to be. The AmazonBasics full synthetic motor oil is a great option that saves you quite a bit of money over other oils you could use in your generator. This oil comes in many weights, so you’re sure to find exactly the oil you need.

    Since it’s synthetic, AmazonBasics oil lasts longer and protects your generator’s engine against wear. The formula is built to resist thermal breakdown while reducing exhaust emissions, making it desirable for anyone concerned with their carbon footprint.

    We had just one problem with the AmazonBasics oil. Usually, there’s a clear stripe on the side of the bottle with graduated markings so you can see how much oil is left. This makes it easy to refill the correct amount, but these bottles are missing that crucial piece. Still, the oil is great and is one of the best generator oils for the money. But it’s recommended that you keep another oil bottle around for precise filling!

    • Priced affordably
    • Fully synthetic
    • Resists thermal breakdown
    • Reduces exhaust emissions
    • Available in many weights
    • Can’t tell how much oil is in the bottle

    3. Generac 0J5140 Full Synthetic Motor Oil – Premium Choice

    Generac 0J5140 Full Synthetic Motor Oil

    Generac is known for making a wide range of exceptional quality generators, so it stands to reason that they know a thing or two about what generators need when it comes to oil. They make generators of every size, from small portable generators to home and business backup generators and industrial power mega generators.

    The synthetic motor oil is the original equipment manufacturer (OEM) oil used in Generac generators. It’s a synthetic base with additional special additives to ensure your generator runs problem-free for many years. Since this is the recommended oil in Generac manuals, it’s the best and safest choice for Generac generators in particular, though it’s also an excellent option for other generators.

    With Generac, you get superior viscosity breakdown protection, so your oil keeps working well over time, not just when you first change it. Furthermore, it prevents sludge and varnish deposits from accumulating inside your engine, ensuring long-lasting performance. Of course, you’ll be paying a premium for that performance since it is some of the most expensive oil we’ve seen.

    • Superior viscosity breakdown protection
    • Prevents sludge and varnish deposits
    • Synthetic base with additional additives
    • Generac OEM for Generac generators
    • Very expensive

    4. STP 18589 4 Cycle Oil Formula

    STP 18589 4 Cycle Oil Formula

    Your generator has a small engine, so why not use oil in it that’s specifically meant for a small engine? It only makes sense. Well, this STP 4-cycle oil formula is made just for small engines, and it includes features to keep them running longer and better.

    STP oil is made to control the viscosity, preventing it from getting thinner as it breaks down. It creates a protective layer at high temperatures to reduce wear and tear, allowing your generator’s motor to last much longer.

    Like most specialty oils, this formula isn’t cheap. It’s far from the most expensive we’ve seen, however. At least this blend offers some improvements for the price, like detergents to keep the inside of your engine clean and corrosion inhibitors to prevent problems while the generator is being stored.

    • Made specifically for small engines
    • Controls engine oil viscosity
    • Creates a protective layer at high temps
    • Reduces engine wear
    • It’s certainly not cheap

    5. Cummins 3265336 Onan SAE 15W-40 Oil

    Cummins 3265336 Onan SAE 15W-40 Oil

    The Onan line of Cummins generators are the best-selling RV generators ever. They’re known for their longevity, lasting many years without issue. If you have one of the iconic generators and want to ensure that it lasts as long as you hope, using the Onan OEM oil is an excellent choice since it’s made for the Onan generators.

    This is the maximum protection formula meant to keep your generator running with low friction and high dependability. It’s expensive oil, but if you own an Onan generator, you already know it’s pretty pricey on its own. We trust the Onan oil in our Onan generators, but if you have another type of generator, you can save money by choosing another reputable brand instead.

    • Perfect for Onan generators
    • Pack of 4
    • Maximum protection formula
    • Wildly expensive

    6. Briggs & Stratton 100074 SAE 5W-30 Motor Oil

    Briggs & Stratton 100074 SAE 5W-30 Motor Oil

    Briggs & Stratton is known for making quality small engines. This 100074 SAE 5W-30 oil is made to work in small engines from a brand with plenty of experience designing and maintaining small engines.

    Briggs & Stratton motors are known for lasting a long time, and its oil could be a part of the reason. It’s fully synthetic, so you can go longer between changes, providing better protection against heat and friction.

    But this is pretty expensive oil, even compared to other blends for smaller engines. In truth, it doesn’t seem to offer improved performance. That doesn’t mean it doesn’t work well; it does. But is it something special that’s worth paying extra for? We don’t think so.

    • Made specifically for small engines
    • Fully synthetic formula
    • Engines last a long time
    • From the small engine experts
    • It’s pretty pricey
    • Doesn’t seem to offer improved performance

    7. Briggs & Stratton 100028 Engine Oil

    Briggs & Stratton 100028 Engine Oil

    As mentioned, Briggs & Stratton is known for making high-quality small gas engines. With this background, we expect them to know about the fluids that need to fill their motors. This 100028 engine oil isn’t meant specifically for small engines, but other oils from Briggs & Stratton are. Although the oil is still warranty certified and recommended in all their motors, we prefer the small-engine specific blend.

    What’s great about this formula is the affordable price. It’s for 4-cycle engines only, so you won’t want to use it in your 2-cycle motor. It comes in a larger 48-ounce container, and you won’t need as many bottles.

    • From a company based around small engines
    • Warranty certified in all Briggs & Stratton manuals
    • Affordably priced
    • For 4-cycle engines only
    • Not made specifically for small engines

    8. ROYAL PURPLE 15W40 Synthetic Diesel Motor Oil

    ROYAL PURPLE 15W40 Synthetic Diesel Motor Oil

    Royal Purple is a controversial motor oil. This blend claims to feature improved compatibility with ethanol fuels. Moreover, the 15W40 synthetic blend is supposed to offer better fuel economy while protecting the emissions system. It also supposedly provides superior defense against corrosion.

    These claims might be true, but in our experience, we could find nothing special about this oil. Our generators ran fine using this oil, but not any better than the other oils we tested.

    Also, it’s worth noting that Royal Purple has been in trouble recently for false advertising. Many claims they had made about their products had been proven false. They’ve likely learned their lesson, but it still leaves a lot of doubt regarding any claims on their oils, including this one.

    • Protects the emission system
    • Improved compatibility with ethanol fuels
    • Better fuel economy
    • Synthetic formula
    • It’s very expensive oil
    • Seems to operate like regular oil
    • Royal Purple has been in trouble for false advertising

    9. Honda 08207-10W30 Motor Oil

    Honda 08207-10W30 Motor Oil

    Honda motors are often heralded as long-lasting motors with top-notch dependability. As such, they’re some of the most expensive generators on the market. If you own a Honda generator, they insist that you continue using Honda oil in your generator. It’s what’s suggested in the manual, and since this oil is OEM for Honda, it’s a great choice.

    That said, if you own a generator other than a Honda, we’d recommend going with another brand. This oil doesn’t offer anything special for the expensive price you pay. You’re essentially paying for the Honda name. This 08207-10W30 blend isn’t even synthetic. For the price, you can get fully synthetic oil from other brands that will suit you just as well or even better.

    • Perfect for Honda generators
    • Overpriced because of the brand name
    • Not synthetic

    10. Delo 400 SAE 30 Motor Oil

    Delo 400 SAE 30 Motor Oil

    The Delo 400 SAE 30 motor oil is available in bulk volumes of up to 5 gallons. That can save you a lot of money over purchasing it by the quart. But that’s our favorite thing about this oil. It’s not synthetic, though it’s priced high enough to make you think it is.

    You can’t use this oil in 2-stroke motors since it’s only compatible with 4-stroke motors. When pouring it, you’ll have to guess how much you’re using since there’s no way to tell on the bottle. It’s a bit cheaper than some brands, but since it’s not synthetic and not made specifically for small motors, we’d recommend skipping it in favor of something that meets those criteria.

    • Available in bulk
    • No markings to see how much you’ve poured
    • Not recommended for use in 2-stroke motors
    • Not small motor specific

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    Buyer’s Guide – Choosing the Best Generator Oil

    There are many different oils you could choose for your generator. But if you put the wrong oil in, you will have some serious issues. If you’re already experienced with small motors, you might not need the following information. But if you’re unsure what to fill your generator with, this buyer’s guide is for you.

    Make Sure You Choose the Right Oil

    If you know little about engines, oil might seem almost trivial. You just grab oil and pour it in, right? Well, you could, but your engine likely wouldn’t function right. There are a few things that you’ll need to make sure of before adding oil to your engine.

    Check the Manual for the Proper Weight

    The most important thing to get right is putting the proper weight oil in your generator. Putting oil of the wrong weight in is one of the biggest mistakes you can make. Luckily, it’s pretty easy to ensure you’re putting the right oil in. All you have to do is open up the user manual for your generator and find the section where it discusses maintenance. Here, it should list precisely which oil you need to add.

    Once you determine what weight of oil your generator needs, you can pick just about any brand at that weight. Any of them will work, but various additives can cause some to perform better than others.

    Synthetic vs Conventional Oil

    Synthetic oil offers quite a few advantages over conventional oil. It resists breakdown for much longer, meaning you can go longer between oil changes. Going further, synthetic oils can withstand higher temperatures, which means they can keep your engine running better for longer.

    Synthetic oil is ideal if you ever use your generator in cold weather. It flows much better in cold temperatures. Also, the engine is easier to start with synthetic oil and puts less strain on the engine. Granted, synthetic oil is quite a bit more expensive than conventional oil. But with so many advantages, it’s a cost we’re always willing to pay.

    OEM is Always Safe

    If your generator is from a major name brand, you can’t go wrong by sticking with the OEM product that’s recommended for your generator. Generally, it is an oil manufactured by the same company. While that oil might not provide superior benefits over other brands, you definitely can’t go wrong by picking what’s recommended for your generator.

    Also, some brands will only honor warranties if their oil is used. Other oils, even of the proper weight, will void the warranty. It’s also possible that certain brands use special additives to make sure their oils work well in their generators since they know precisely what their machines need to run at peak performance.

    Ensure You Get the Right Amount

    Another important consideration is how much oil you need. Oil comes in quarts, gallons, 5-quart containers, and even 5 gallons. Of course, you’ll unlikely need 5 gallons of oil to fill your generator. Still, you should know precisely how much oil you need to avoid overbuying and, more importantly, overfilling.

    To determine what your generator requires, check the manual and find the maintenance section. It should tell you exactly how much oil you’ll be replacing. Alternatively, this information is most likely available online as well.

    How Often Should You Change the Oil?

    It’s important to keep up with the maintenance of your generator if you want it to function at its best for many years. As such, you’ll want to follow the manual’s guidelines regarding how often you should change the oil.

    As a rule of thumb, new generators usually need their first oil change after 25 hours. After that, you’ll want to perform regular oil changes after every 50 or 60 hours of use. But again, you’ll need to confirm that in the manual for your generator.

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    There are several oils on the market with varying formulas and features. They span different weights and come from various manufacturers. It could be catastrophic if your generator isn’t working when needed, which is why we’re making recommendations that we’re confident won’t let you down.

    Castrol EDGE high mileage is our top pick. This fully synthetic formula provides increased fuel economy and protection against high-temperature oil thickening. You’ll get 30% greater oil film strength and reduced breakdown and friction.

    The AmazonBasics oil comes in many weights and is one of the most affordable oils we’ve seen, though it’s still fully synthetic and resists thermal breakdown while offering reduced emissions.

    And it might be expensive, but Generac full synthetic motor oil is our premium choice. It comes from a brand that specializes in generators of all sizes, and it is Generac’s OEM oil that’s recommended in their generators. It has a synthetic base with special additives that can keep your generator running longer, with superior viscosity breakdown protection that prevents sludge and varnish deposits in the motor.


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