A Guide to Running Synthetic Oil in a Generator

Your generator is one of the things that must be constantly maintained and kept working with new tools, more oils, and constant filter changes. One of the things that many people do is move towards synthetic oils that are usually less expensive and can serve multiple purposes.

Synthetic oil is perfect for generators because it handles temperature changes well, cleans your engine while in use, and is usually less harmful to the environment than alternatives. There are many types of synthetic oil with various additives to make it capable of handling nearly anything.

The choices in your synthetic oils will decide how well your generator can run on it, and many people will not be entirely sure what the advantages are. Each type of generator runs better when you get a specific type of synthetic oil, making a choice essential and sometimes extremely hard.

Is Synthetic Oil Better for Generators?

Because synthetic oils are better at creating films and working under higher temperatures, they are much better for smaller engines than mixed or natural oils. Synthetic oil can handle much higher engine temperatures, which further helps everything work when under pressure.

Small engines usually used on portable or standby generators will run significantly hotter than larger ones. As the pistons are moving faster and the cooling system is most of the time only air-cooled, the oil needs to be able to handle very high temperatures.

We always recommend using synthetic oil with your generator either way. If the temperatures drop well below zero degrees in the winter, the oil will not freeze and become utterly damaging to the system when you start it.

How Do You Know When You Should Use Synthetic Oil?

If you have to replace the oil in your generator more often than not, or when you find that the oil in your generator has turned entirely black. Both of these are signs that the current oil you are using in your generator cannot handle the engine’s hard work and heat.

When you are doing a service for your generator, you want the oil that is coming out to be slightly discolored but not completely black. If the oil is completely black, it means that the oil has been run far above its intended operating temperatures.

Further, you might not have serviced the generator enough, which caused the oil to expire, with natural oils expiring much faster than you may expect. Synthetic oils have expiration dates; however, they take significantly longer, and you can run them in the generator without worry.

Is Synthetic Oil Better Than Natural or Combination Oil?

Yes, synthetic oil is better for your generator than natural or combination oils as they are usually imprecise, and the chemicals in them are not as accurate. Natural oils are combinations of naturally found chemicals but not always at the same ratios as the next batch may have.

Synthetic oils are always precise combinations of chemicals from the manufacturer made to handle the conditions of specific engines. Further, natural oils can become acidic much faster than synthetic oils, which can severely damage the inside of your generator, shortening its life.

Usually, you will find that older generators require natural oils because synthetic oils are not always better. However, with modern technology, all synthetic oils have drastically increased quality and will always be better for your generator, even if it is an extremely old generator.

Why Is Synthetic Oil Used?

Now that we know almost everything about synthetic oils, including which oils will work the best with your generator, we must consider why people use them. Many people are still stuck believing the same things about synthetic oils when companies first brought them to market in the 1950s.

However, the oils have changed drastically and are now actually more capable than any other type of oil, with many being much more eco-friendly. There are four reasons why synthetic oil is better than natural oils, with every type of synthetic oil having its unique advantages.

1. Temperature Resistance of Synthetic Oil

Synthetic oils can resist extremely low temperatures and extremely high temperatures, with most able to comfortably handle both. This means you can run the engine in the morning at below zero temperatures until the afternoon when it reaches peak temperatures.

The ability to handle all temperatures has meant that synthetic oils have replaced almost all other types of oils. With nearly any engine reaching higher temperatures, they still do not deteriorate when run to the extreme because their max temperature is far above the engine’s operating temperature.

2. Engine Protection

Because synthetic oil helps coat specific engines and keep them working smoothly, they offer better protection than natural oils. An easy example of this is the film created, with natural oils eventually becoming too gunky on the inside of the engine.

Synthetic oils rarely become like this and will usually create a thinner film that makes it harder for the engine to move. Further, the oil will keep damaged parts and metal flakes suspended in them much longer than natural oils, which may settle down faster.

3. Lower Consumption

Synthetic oil lasts longer and is more burn resistant than natural oils, which means they last much longer than the other oils used. As the generator turns and creates power, naturally, the amount of oil used increases, which is not as big a problem when using synthetic oils.

We have seen many people that forget to service their generator regularly, that they have the challenge of trying to clean out the dried-out natural oil that was in previously. Synthetic oil does not get used up as faster, lasting longer, and allowing you to have some leeway between generator services.

4. Engine Cleaning

The one claim that you will always see people and companies make is that oil is cleaning your generator’s engine from the inside. Synthetic oil does do this, removing rust and other contaminants from the inside and keeping them suspended for much longer than they would be when using natural oils.

This naturally cleans your generator as it is working, which means that when you are servicing it, you are essentially giving the entire inside a clean with the new oil. If you have enough oil and a system that has gone a while without a service, it will be beneficial to run the engine with new oil and then drain it out and add more in.

What Are the Top Seven Synthetic Oils for Generators?

We need to look at the best first to understand why synthetic oils are better and how to run your generator in the best possible way with these lab-manufactured oils. Usually, we provide a range of oils from synthetic and organic manufacturers or mix the products.

However, for the best performance from your generator, we recommend just sticking with synthetic since the cost is less and you can comfortably use the oil without challenge. Further, the more remote you are, the more likely it is that your supply of synthetic oil won’t run out.

1. Pennzoil Ultra Platinum Full Synthetic 5w-30

We recommend the Pennzoil Ultra-Premium for older generators as it is excellent at helping to keep engines clean. This means that as a part of the high operating temperatures that the 5W-30 can operate at, it will also help keep the engine going.

Generally, the Pennzoil 5W-30 can handle machines that are running hotter with pistons that are moving faster. It makes it ideal for small engines; portable generators have small engines and usually run at their maximum speed and power throughout their lifetime.

2. Mobil 1 Extended Performance Full Synthetic Motor Oil 5w-20

The Mobil 1 5W-20 full synthetic oil is the one we recommend using when your generator will be running in the desert one day and then near arctic temperatures the next day. Not only can the oil withstand temperatures of -30 degrees Fahrenheit, but it can also handle up to 500 degrees Fahrenheit.

While doing that, it will easily help the engine run at these temperatures, keeping the metal from warping or becoming too weak to the temperature changes. Further, it can handle just around 100 hours of operating with the generator, making the oil perfect for your generator of any size.

3. Royal Purple 44154 04154 Api-Licensed Sae 15w-40

If you run a generator that uses slightly richer fuel, the Royal Blue 15W-40 is great for medium to larger generators to be oiled. Because it does not focus on anything specific, this fully synthetic oil is a great way to ensure that your medium to a large generator runs just like new.

Unlike the other synthetic oils that we have listed here, the Royal Blue 15W-40 is for a simpler servicing of your generator. Instead, the slightly improved price and similarity to handling both heat and cold allow you to service your generator with the same oil every time without facing exorbitant costs.

4. Shell Rotella T6 Full Synthetic 5W-40

You may think that the only synthetic oil is for petrol or gas generators; however, the Shell Rotella 5W-40 is a full synthetic oil meant to be used only with diesel engines. As diesel is naturally lubricating, this oil serves other purposes more than it does the lubrication of the pistons.

Shell Rotella 5W-40 is made to survive the sheering that can happen as your generator’s engine goes through heating and cooling cycles. Diesel engines are naturally oiled by their diesel fuel, making the oil used slightly different from standard oil able to handle the higher pressures in these engines.

5. Liqui Moly 2040 Premium 5W-40

Older generators usually need an oil capable of helping protect the inside of the machine with something called a film. This layer of oil forms over areas not deep within the oil pan, protecting the machine from rust and anything that may damage the inside.

We always recommend that you use an oil that can create a film across the inside of the engine when it is older. The liquid moly 5W-40 is known for creating a thicker film throughout the engine, making it perfect for keeping your older generators from being damaged from older damage.

6. Castrol 03100 GTX High Mileage 5W-20

The Castrol 5W-20 is the oil you can most likely find on Amazon or at the nearest gas station on the corner of your street. It can be used with most petrol generators and will easily help you keep it clean, cool, and running for hours on end without having to stress whether or not your engine is safe.

We recommend using Castrol oil when you are not entirely sure what will be the best for your generator, as the manufacturer specializes in most fluids that go inside an engine. You can buy the oil in small quart jugs or larger six-gallon bottles to fill smaller or larger generators.

7. Amazon Basics Full Synthetic Motor Oil

The simple fact is that this is the basic oil for your generator, allowing you to comfortably use it for all of your generators and know that everything is the same. Amazon basics usually focus on providing something that is of similar quality to other oils on the market.

However, because this oil is just aiming to be the basic oil, it does not always have the same cleaning, film creating, or heat protection. It will always be best to use the Amazon basics for a generator that you are using in a moderate climate and only when you know you will not use it often.


Synthetic oils are one of the best things you can add to your generator as they will clean the inside and ensure that the machine is always performing at its best. You can replace the natural oils in all generators with the right synthetic, making the entire engine run cleaner and cooler.

Always remember, technology is always improving on synthetic oils, while natural oils have been the same for more than a hundred years.


Hubert Miles

I've been conducting home inspections since 2002. I'm a licensed Home Inspector, Certified Master Inspector (CMI), and an FHA 203k Consultant. I started PickGenerators.com to help people better understand whole-house and portable generators.

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