No matter the quality of your generator, if you don’t use the right oil, it will gradually seize up. Parts will become quickly worn and degraded, which means that maintenance and repair costs will skyrocket. Buying the best oil for your generator will help ensure that you enjoy a long, trouble free life.
In the best oil for generator, 2019, guide, we have tried to cover a variety of oils, including those that are suited for use in cold weather, and for use in a range of different generator types.
We have tested dozens of oils in various running conditions, in order to bring you a list of the best you can buy. We will look at some of the best manufacturers, the most common types of oil, whether mineral or synthetic oils are best, and even what those nonsensical numbers (e.g. 5W-40) mean.
TOP 5 Generator Oil Rundown
Honda 10W-30 Motor Oil: designed primarily for use with Honda generators, this 4-stroke 10W-30 oil is a little pricey but it will maximise efficiency in your Honda generator engine and is our top choice.
Briggs & Stratton 30W Oil: a cost effective generator oil for use in warmer conditions, and the detergent oil will keep the motor clean.
Cummins Onan 15W-40: suitable for diesel and gas generators, works well with engines that run at very high temperatures.
Shell Rotella 15W-40: not suited to low temperatures, works well at high temperatures and costs less than most of its competitors.
Husqvarna XP+ 2-Stroke Oil: the best of the bunch, when it comes to choosing a 2 stroke oil especially because of its low smoke production.
How To Choose The Best Oil For Your Generator
Most of us know that car engines need oil to run smoothly, and this is true of any motor. The parts of a motor rub against one another while in operation. This causes friction and can wear the parts down. A build up of friction also means that the motor has to work harder in order to run, which means even more wear on the parts, and considerable wear on the wallet.
Oil acts as a lubricant, which reduces friction and keeps the engine running smoothly. A generator is just a motor, or engine, and it needs the same lubrication as your car engine.
Oil also serves several other purposes. It reduces heat, can clean the engine, and reduces oxidation that leads to corrosion of engine parts. The better lubricated the engine parts, the more slippery they become, which means that they are easier to operate and will cost less in fuel running costs.
So, oil is important to your generator. But, not all oils are suitable for all engines. Use the wrong oil and it could have as detrimental an effect as having no oil.
Know Your Generator
The first step to choose the best oil for your generator is knowing your generator. Most modern generators have 4-stroke motors, although some 2-stroke variants do still exist. You need different types of oil for 2-stroke and 4-stroke engines, so check this.
While a 4-cycle engine will have separate reservoirs for oil and fuel, a 2-stroke engine requires a mix that is put in the same tank. You can create your own mix of fuel and oil, or buy one that is pre-mixed.
Read the manufacturer’s guide: not only will this tell you whether you have 2- or 4-stroke model, but it will also give some recommendations regarding the type of oil you want, how often you should be changing it, and some general guidelines on how to run your generator more efficiently.
Mineral Or Synthetic?
There are two basic types of oil that can be used in a generator – synthetic or mineral. Mineral oil is sometimes referred to as real oil.
Synthetic oil has been developed to be more effective and kinder on generators, especially on 2-stroke generators. These engines operate at higher temperatures, and synthetic oil offers greater consistency at high and extreme temperatures. It also lasts longer, which means that oil changes can occur less frequently.
Synthetic oil tends to work better as soon as you start the generator. This means that it will lubricate the engine immediately, unlike natural oil which takes time to reach the necessary viscosity.
It might cost more per bottle but, over time, we believe that synthetic oil will save you money on repairs, maintenance, and oil replacement.
There’s also the environmental consideration: natural oil uses more crude oil, which is a fossil fuel and a finite resource. Synthetic blends and pure synthetic oils use less or no crude in their production, so are kinder on the environment.
Performing Regular Oil Changes
While it is important that you have an adequate amount of oil and that it is in good condition, you don’t want to have to keep changing the oil because this will cost you more money in the long run.
Always check the operator instructions to determine how often you should change oil. Typically, this is measured in the number of hours that you run a generator. Most new generators demand an oil change after 25 hours, with further oil changes recommended every 50 hours, although some generator and oil combinations can last as long as 200 hours without having to undergo a change.
Manufacturer instructions are written according to ideal operating conditions, and assuming that the oil in your generator remains in good condition. If you regularly start the generator in extreme conditions or if you have noticed additional sludge or debris in the oil, it is a good idea to perform an oil change, even if it has not been running for the recommended number of hours.
What About Those Numbers?
When first looking at generator oil, one of the most baffling elements is the array of codes and numbers that appear in some of the names.
What does SL 5W-40 mean, for example?
The category of oil, in this case SL, is the API Service Classification. When cars and engines were first built, they used SA class oil, but this became obsolete in the 1920s. The current classification is SN, but it is still considered acceptable to use SM, SL, and SJ grade oils. The most recent, SN grade, oils are considered the best. They have been developed to improve protection for pistons, have better sludge control, and offer better fuel economy and engine cleanliness.
Some oils have a Winter rating, in the example above, this is the 5W figure. The W stands for Winter and the number preceding it is the viscosity of the oil at winter temperatures. The lower the number, the thinner the oil in these conditions, and the better the generator will start at these temperatures.
The second number, 40, represents the oil’s viscosity at normal temperatures. Thicker oil maintains film strength at high temperatures. In hot conditions, your generator will benefit from an oil with a higher viscosity at normal operating temperatures.
Most manuals tell you to choose an oil according to the typical conditions in which you will use it. If the generator will only be running at temperatures of 0C or above, then most manuals recommend an SAE 30. Temperatures below 0C and above -20C and you should opt for 10W-30. In all conditions, manufacturers recommend that a good quality synthetic 5W-30 will run efficiently.
Most oils fall into the 5W-30 or 10W-40 range, but not all.
5 Of The Best Oil For Generators review 2019
Taking all of these factors into account, these are the 5 best oils for generators we have found:
Honda Motor Oil 10W-30
A mineral engine oil by Honda, for Honda 4-stroke engines that offers the reliability of the Honda name and excellent results when used in generators. It is also suitable for other small engines.
Although the 10W-30 oil is a mineral oil, it performs surprisingly well at startup. Mineral oils tend to take longer to reach the required viscosity once you start the engine, but during testing, we found that Honda’s oil not only led to a smoother operating generator but it reached that point more quickly than other oils.
It meets the latest API SN Classification, which means that it adheres to the American Petroleum Institute’s requirements for engine oil.
Lastly, but by no means least, it is manufactured and supplied by Honda: a name that is synonymous with reliability and performance. It has been designed specifically for use with Honda engines, but this oil has shown to be effective in any generator that requires 10W-30 oil.
The only real downfall is that it is pricey for a mineral oil. In fact, it has a similar price tag to a lot of synthetic oils.
Pros
- The Honda Name
- Latest SN API Classification
- Great startup and ongoing performance
Cons
- Pricey for a mineral oil
- Mineral oil
Briggs & Stratton SAE 30
Briggs & Stratton is one of the most widely recognised names in gasoline engines in the USA. It has headquarters in Wisconsin and offices around the world, such is its popularity. Not only are they known for making durable and rugged engines, but for the manufacture and supply of equally high quality oil.
The Briggs & Stratton 30 oil is no exception. It is ideal for use in warmer climates, and may not fare well in extreme cold temperatures. It is a mineral oil, which means that it costs less than a lot of its synthetic counterparts, and while it has been developed for use in Briggs & Stratton’s motors, it will work equally well in any engine that specifically requires SAE 30 oil.
One of the key features of this oil is that it is a detergent oil, which means that it will work especially well preventing sludge buildup that can ruin your generator, and your day. It is Classified as an SJ oil by the API, which means that it is still current, although newer regulations do exist.
Pros
- Efficient at high temperatures
- Lower cost than synthetic alternatives
- Detergent oil prevents sludge
Cons
- Mineral oil
- SJ classification
- Not designed for low temperatures
Cummins Onan 15W-40
Cummins manufactures a host of engines, filtration, and power generators, including its Onan range of generators. They are a well respected brand, thanks to products like the 15W-40 oil.
The Cummins Onan 15W-40 oil is designed primarily for diesel generators, but it also works well with engines and generators that run at very high temperatures. Whether the temperature is governed by local environment, the conditions that your generator are kept in, or the style and operation of the generator, if it runs hot, then this is a solid choice of oil.
This oil does a great job of reducing wear on engine parts, and it will also reduce the diesel usage in your generator, saving you money and ensuring efficiency from your generator.
Pros
- Designed for diesel generators
- Highly efficient at high temperatures
- Cummins reputation
Cons
- Not ideal for cold conditions
Shell Rotella 15W-40
Shell is one of the largest manufacturers of petrol and oil products in the world. It is ranked as the ninth largest company in the world and is the largest energy company. Founded more than 110 years ago in London, it has developed an incredible reputation within the industry, and its petrol and oils are used around the world, not only in cars and vehicles, but in generators and other engines.
The Shell Rotella 15W-40 range can be used in diesel and gas engines. It has a C rating for diesel and an S rating for gasoline, making it a true multi-purpose oil. It is a synthetic oil so it will cost more than the mineral alternatives, but we have found that it will reduce wear and tear on engine parts and will reach optimal temperature more rapidly than other oils. We have also found it to be cheaper than a lot of other 15W-40 oils on the market.
The 15W-40 oil type is rarely recommended in manufacturer instructions, because it doesn’t have the best winter rating, and this does mean that there are slim pickings when it comes to choosing the best of this type of oil. Fortunately, though, the Shell Rotella range is efficient and effective.
Pros
- Costs less than most 15W-40 oils
- Synthetic oil
- Works with diesel and gas generators
- Shell name
Cons
- 15W-40 is rarely recommended by generator manufacturers
- Not ideal for low temperatures
Husqvarna XP+ 2-Stroke
Most generators are 4-stroke models, but there are still a lot of older 2-stroke models out there, and some people prefer this simpler type of engine. Because 2-strokes are less popular, it does mean that your oil options are also more limited.
Thankfully, the Husqvarna XP+ range of engine oil comes from a company that specialises in the manufacture of this type of engine, and it shows.
The oil is great for keeping operating temperatures down, produces very little smoke compared to other oils of a similar nature, it is a synthetic blend, so it might cost more than natural oils but will reduce running costs.
The oil includes fuel stabilizer which provides efficiency at lower temperatures. This increases engine protection while also reducing the amount of engine smoke from your generator. Simply put, if you have a two stroke engine, this is the best oil we have found.
Pros
- One of few 2-stroke oil options
- Synthetic oil
- Low smoke production
Cons
- Semi-synthetic oil
- More expensive than mineral oils
Conclusion
It is difficult to pick a single oil as being the best generator oil, because it depends on the type of generator you have. If you have a diesel generator, we recommend the Cummins Onan 15W-40 oil. For 2-stroke generators, the Husqvarna XP+ is your best option, and for Honda generators, the Honda motor oil is our pick of the bunch.
In fact, the Honda oil just about shaves it as our overall pick.
While it is a little on the pricey side for a minera l oil, it really does offer improved efficiency and better running conditions for your generator. It also bears the Honda name, which is a mark of quality when it comes to 4-stroke generators.