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Best Synthetic Oil for Your Generator - The Complete Buying Guide

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Synthetic oil is best for generators because it is resistant to temperature changes, cleans the engine as it runs, and has less of an impact on the environment than other types of oil. Synthetic oil comes in a wide variety and can be tailored to meet practically any need thanks to its many benefits.

Many people don't know that different synthetic oils can improve the performance of their generators in different ways. Because different types of generators require different types of synthetic oil to function optimally, making a choice is often vital and often challenging.

Why or why not synthetic oil for generators?

For smaller engines, synthetic lubricants are preferable over blended or natural oils due to their superior film-forming and high-temperature performance. Everything functions better under pressure because synthetic oil can handle far higher engine temperatures.

Portable or permanent standby generators often include smaller, hotter-running engines than larger ones. Since the pistons are moving at a faster rate and the cooling system is usually just air-cooled, the oil must be able to resist extremely high temperatures.

For the best results from your generator, you should always use synthetic oil. Even if the temperature outside drops well below freezing, the oil won't solidify and cause irreparable damage the next time the engine is started.

The greater expense of synthetic oil is reasonable

Synthetic oil is more expensive than conventional oil, yet it is still a great investment.

Synthetic oils are more expensive than conventional oils because they contain detergents, anti-wear chemicals (such as zinc dithiophosphate), and other ingredients. They improve the lubricating and cooling properties of synthetic oils by including additives.

Conventional oils, on the other hand, often contain far fewer additives. This is due to the fact that their underlying elements are typically of low quality, making it illogical to invest heavily in expensive additives to try to improve the oil.

The assumption that replacing conventional oil with synthetic oil is harmful is false. There is an equally widespread misunderstanding that some sort of break-in time is necessary for the transition to go well. That is not the case.

Synthetic oil is an option that can be substituted for conventional oil at any time and the engine does not have to be broken in with conventional oil first. 

Synthetic oils are the best option for your generator. Also, once you settle on a synthetic oil brand, be consistent with it. It's not a good idea to often switch brands of synthetic oil because no two are exactly comparable.

When should you switch to synthetic oil

If you discover that you need to change the oil in your generator more often than usual, or if the oil has become entirely black, it's time to replace the oil. These are both signs that the oil in your generator is either thin or too old to protect it from the heat and stress it experiences.

If your generator is being serviced, you want the oil to be dirty looking but not completely black. When oil becomes completely black, it has been heated to a far higher temperature than is safe.

Natural oils expire more quickly than you might expect, therefore you may not have given the generator the upkeep it needed to extend its life. Since synthetic oils last so much longer, you can keep using the generator without worrying about reaching their expiration date.

Is synthetic oil better than natural oil or a mixture of the two?

As natural and blend oils have a tendency to be less consistant and include less specific chemicals, synthetic oil is recommended for your generator. Natural oils are chemical combinations that occur naturally but whose exact composition might vary from one batch to the next.

Manufacturers of synthetic oils typically formulate their own unique chemical blends to meet the specifications of various types of engines.

Furthermore, unlike synthetic lubricants, natural oils have a much higher propensity to turn acidic, which can badly damage the interior of your generator and shorten its lifespan.

Natural oils are often required for older generators because synthetic oils might actually clean them TOO well, and release too much sludge too quickly. Synthetic oils, which are of much superior quality thanks to modern technology, are always preferable, even if your generator is relatively old but be careful when doing the switch.

Using a high-quality synthetic oil

Some generators may require special oils in order to function. Manufacturers will typically list the oil viscosity range within which their generators will operate. Synthetic oils with the viscosity number recommended by the manufacturer should be used.

The oil's resistance to flow is quantified by its viscosity index. Diesel engines have slightly more stringent viscosity requirements since the oil's ability to flow properly in hot and cold engine conditions is temperature dependent. If the oil has a high viscosity, it is able to resist flow effectively.

You'll become familiar with the convention of using two numbers, such as 10W-30, to describe the viscosity of engine oil. The first number after the "W" (winter) indicates the oil's resistance to flow or thinness at temperatures of zero degrees Fahrenheit (about -18 degrees C).

Since W denotes winter, this number describes the oil's ability to resist thickening when exposed to low temperatures. Moreover, the lower this value is, the less likely it is that the oil will thicken when it is cold.

Synthetic oils are great winter lubricants and should be used by everyone who runs their generator throughout the colder winter months.

The oil's behavior under high temperatures is described by the second number, 212 degrees Fahrenheit (100 degrees C). The greater the number, the less the oil will thin out in hot temperatures, and vice versa. Consequently, a 10W-30 oil will thin down faster in warmer conditions than a 10W-40 oil.

Use of synthetic oil in your generator has many advantages

The quality standards for the base oils used to produce synthetic oils are often greater than those for the base oils used to produce conventional oils.

Synthetic oils have superior chemical stability and are far more resistant to degradation and loss of desirable properties than their natural counterparts because of the higher quality of their basic oils.

Because of the complex process needed to produce them, synthetic oils may be tailored to meet the unique needs of current oils and are cleaner than their conventional counterparts. Because of this, engines would benefit more from synthetic oils than from regular oils. Some more benefits of synthetic oils are:

Temperature tolerance of synthetic oil

Unlike mineral oils, synthetic oils may be used in both very hot and very cold conditions without breaking down. The engine may be run in sub-freezing conditions in the morning and continue working until it reaches its hotter temperatures in the afternoon.

Because synthetic oils can function in any temperature range, they have largely replaced natural oils. Since their maximum temperature is higher than the engine's working temperature, they remain in good condition even when subjected to extreme conditions.

The importance of engine safety

Because of their ability to coat certain engines and maintain smooth operation, synthetic lubricants offer superior protection to natural oils. The coating that forms in an engine when the natural oils inside become too greasy is a good example of this.

In contrast to conventional oils, synthetic oils rarely reach this stage and instead form a thin covering that impedes the engine's motion. In addition, the oil will keep damaged parts and metal flakes suspended in them for a lot longer than natural oils would.

More efficient

Synthetic oil is superior to all other oils because it lasts longer and is more resistant to flames. Synthetic oils alleviate this problem somewhat, but it still increases as the generator spins and produces energy.

You can have a tough time cleaning dried-out oil from their generators because they didn't do routine maintenance. As synthetic oil does not decrease as rapidly as conventional oil, you can go longer between generator maintenance checks.

Cleaning the engine

Deposits form on moving parts as the oil in your generator makes its way through the engine. Using conventional oils will result in the accumulation of sludge, which will have a negative impact on your engine's efficiency and lifespan over time. Synthetic oils, on the other hand, tend to form less sludge since they contain less impurities.

Synthetic oil is much more effective than natural oils at removing rust and other contaminants from within a machine, and it also keeps these particles suspended for much longer.

Due to the natural cleaning process that occurs when the generator is in operation, replacing the oil is like giving the entire inside a thorough cleaning. If you have enough oil but the system hasn't been serviced in a while, it's best to run the engine with fresh oil before draining it and adding extra.

Raise in viscosity

Synthetic oils provide greater stability and viscosity throughout a wide temperature range. The ability of synthetic oils to maintain fluidity at subfreezing temperatures and to resist excessive heat is beneficial to the year-round performance of your generator.

This is another often asked query relating to synthetic oils. The answer to this question is an emphatic yes. You should expect to go longer between oil changes when using synthetic oil in your generator. However, the brand of synthetic oil you choose also makes a difference.

To find out how often you should replace your oil, consult your generators manual. 

Best Synthetic Oil for Your Generator

You should always by synthetic oil from brands you trust, here are my favorites:

Castrol 03100 GTX 5W-20

Castrol 03100 GTX High Mileage 5W-20 Synthetic Blend Motor Oil, 5 Quarts

You may acquire Castrol 5W-20 oil from places like Amazon or your local gas station. It's compatible with most gasoline generators and makes it easy to keep the unit operating for long periods of time while minimizing noise, heat, and stress.

Since Castrol is an industry leader in producing a wide variety of engine fluids, it is our recommendation that you purchase their oil whenever you are unsure of what to use in your generator. The oil is available in both one-quart and six-gallon containers, making it suitable for both small and big generators.

Shell Rotella T6 5W-40

Shell Rotella T6 Full Synthetic 5W-40 Diesel Engine Oil (1-Gallon, Single Pack)

It's easy to assume that gasoline and gas-powered generators are the only possible users of synthetic oils, but Shell Rotella 5W-40 is a totally synthetic oil made specifically for diesel engines. Diesel is naturally lubricating, therefore this oil has additional use beyond just keeping the pistons smooth.

The engine in your generator experiences thermal cycling, and Shell Rotella 5W-40 is made to withstand the sheering that may occur during these transitions. Oil used in diesel engines is slightly different from regular oil since diesel fuel naturally lubricates diesel engines.

Mobil 1 Extended Performance 5W-20

Mobil 1-123840 Extended Performance High Mileage 5W-20; 5QT, Gray

We recommend Mobil 1 5W-20 full synthetic oil for use in your generator when it needs to function in extreme temperatures, such as the desert one day and near the arctic the next. The oil can endure heat of 500 degrees Fahrenheit and cold of -30 degrees Fahrenheit.

It will be easy to keep the engine operating at these temperatures if the metal doesn't distort or weaken too much in response to temperature changes. With an oil change every 100 hours, your generator, no matter how big, will be good to go.

Amazon Basics Full Synthetic Motor Oil

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

Amazon Basics is known for providing oils that are competitive with those sold by other companies but usually at a cheaper price.

This oil's primary goal is to serve as the base oil, hence it might not have the same cleaning, film-making, or heat-protecting abilities as other oils. When using a generator in a mild temperature and when you don't plan on running it very often, you can stick with the Amazon basics.


It's general knowledge that generators can't function properly without motor oil. Because of this, you need to be selective regarding the oil used in your generators. Concerns about the safety of using synthetic oils in generators are a common source of enquiry from generator owners.

Most modern generators can use synthetic oils instead of conventional oils. Synthetic oils are superior to conventional motor oils as a lubricant for generators and can extend engine life. Use a premium SAE synthetic oil, such as Castrol's, in the 5w30 or 10w30 range.

Avoid using synthetic oil in older generators, since it might damage the machines and cause deposits to break loose.

If you put the wrong kind of oil in your generator, its life expectancy could be drastically reduced, if not completely ruined.

About Tom Bell

Hey, I’m Tom, the owner of Generator Reviews! I built this website to help you get the very most out of your generator and select the correct one for your personal circumstances. This site contains reviews of virtually every generator, detailed buying guides, as well as maintenance advice to help you keep yours in tip-top shape!


Generator.Reviews is an independent review business. I am not affiliated with any manufacturers and do not accept paid reviews. When you buy through my links, I may earn a commission which helps me to maintain this website and keep the reviews coming your way!

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