The 5 Best Oils for Generators In 2020 – Reviews And Buying Guide

According to toolspost expert team Shell Rotella T6 Full Synthetic Oil is the best oil for generators in 2020.

It is an often overlooked fact that the most important moving part in any engine is its oil. Without oil, engines don't work. When it comes to generators, having the right oil and maintaining it correctly, could be absolutely vital. 

Generators are by definition important pieces of equipment; if you're depending on one for heating, cooling or pumping water, you really want to make sure your oil is up to scratch.

Best Generator Oil Comparison Chart



Liquid Vol.




Shell Rotella T6 Full Synthetic Heavy Duty Engine Oil

55 Gallon

432 Lbs

35 x 22.5 x 22.5 inches

Shell Rotella T6 Heavy Duty Oil

1 Gallon

23.6 Lbs

13.8 x 12.7 x 8.7 inches

48 Fl. Ounces

3.08 Lbs

4.5 x 4.5 x 8.5 inches

32 Fl. Ounces

1.88 Lbs

4.4 x 4.4 x 8.9 inches


1.95 Lbs

2.4 x 4.1 x 10.6 inches

32 Fl. Ounces

1.93 Lbs

8.8 x 4.3 x 2.6 inches

Different types of engine need different kinds of oil, and generators are specialist machines. When used with the right oil, they should never let you down.

Our Top Picks Of Best Oils For Generators 2020 Reviewed

1. Honda 08207-10W30 Motor Oil

This high quality motor oil is sold by Honda specifically for use with its own products. It has Honda as its Original Equipment Manufacturer (OEM) on the bottle, and is designed for Honda four stroke engines, used by generators, lawnmowers, scooters, go karts and mopeds.

As such, it is highly recommended that you only use this oil if you have a Honda generator. It does its job as soon as you start up, which is extremely important in two stroke engines.

Honda 08207-10W30 Motor Oil

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This oil will make your generator engine more efficient, even if you use it as a top up for oil of a different spec. It is on the high side when it comes to price, however.

2. Briggs & Stratton 30W Engine Oil - 48 Oz. 100028

From Briggs and Stratton comes this excellent engine oil which is perfect for generators. B & S are one of the best known engine manufacturers in the US, and market oils which make their engines perform better and last longer.

Luckily for us, that means they work great on other engines too. This specially mixed motor oil has some great plus points for generator engines.

 Briggs & Stratton 30W Engine Oil

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It is a detergent oil, meaning it keeps your engine clean by not allowing a build-up of waste products. Its formulation is designed to work best in high temperatures, such as those in generator motors. It is also great value and comes in a handy sized bottle.

3. Generac Full Synthetic Motor Oil 5W-30 SN Quart Bottle Part# 0J5140 (qt)

Generac Power Systems are at the forefront of generator technology, and this product is part of that process.

This is a synthetic oil, which is becoming increasingly popular with users of high temperature motors in general, and generators in particular.

Traditional motor oil, refined from crude, changes over time and exposure to heat. Basically, it becomes thicker.

Generac Full Synthetic Motor Oil

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For a lubricating motor oil, this obviously presents massive problems. Thicker oil cannot move around the workings of your motor like it's supposed to, and your engine jams. If you've ever had this happen, you will appreciate the value of synthetic motor oil. This oil is fully synthetic and great value.

4. Cummins 3265336 Onan SAE 15W-40 Oil - 1 Quart

Cummins generators are hugely respected throughout industry, and their Onan brand is part of their reason for having such a great reputation. This one-quart bottle of engine oil has everything you'd expect from such industry leaders.

Cummins use this oil for their own generator motors of a certain type; the type you and I use. The oil is tested in their own factories to make their engines work at their best.

Cummins 3265336 Onan SAE 15W-40 Oil

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It is designed for diesel engines but works perfectly well in gas powered generators as well. It is formulated to increase engine efficiency by resisting viscosity caused by very hot engines.

5. Briggs & Stratton SAE 5W-30 Synthetic Small Engine Motor Oil

This excellent synthetic oil comes from Briggs and Stratton. It is designed for use in small four stroke engines such as those found in some generators.

As well as conquering the viscosity problem posed by traditional motor oils, this is also a detergent oil which will keep your engine's working parts trouble free. This is great for fuel efficiency and for longer engine life.

Briggs & Stratton SAE 5W-30 Synthetic Small Engine Motor Oil

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Synthetic oil is also known for its ability to start working as soon as you fire up. Again, as its molecular structure doesn't need warming up to start lubricating properly, you can trust this oil in the winter.

Quick Tips To Buy Best Oil for Generators

Buying the right generator oil is vital to the functioning of your engine. As we have seen, generator manufacturers themselves make oils which give their own products the best performance and longest life.

While these are some of the biggest names in the generator market, engine oil sold for use in these engines and others of similar size and speed, can come from brand names more associated with the motoring industry.

It pays to be careful. Choosing the wrong oil could be expensive and may cost you more than money.

Here are some things to bear in mind when choosing your generator's engine oil:

Know your generator

There is a wide range of power generators on the market, making the choice of oil more difficult than it used to be. By and large, portable generators were made by certain companies, to work with pretty standard oils;

so, if yours broke down on a campsite, you could probably ‘borrow’ some from another, friendly camper.

These days, generators are more readily available in types of manufacture which require specific upkeep, including generator oil. Manufacturers will always recommend their own brand of engine oil;

But it is still the case that other brands may well work just fine. While the choice is bigger, you may find a brand of oil on the market which is actually better value.

A lot of people who depend on generators have the same one for years and years. Reliability is by far the most important factor in their use.

This goes for the oil which keeps them running; and as the saying goes, if it isn’t broken, don't fix it. In today's market, that might not be such good advice. Do some research.

Real or Synthetic?

This is a question often rightly asked when it comes to oil for generators. While users of other engines for different uses might not have the choice, the increasing call for synthetic lubricating oil is often from users of small engines such as these.

The main reason for this is the temperature these motors reach. Two stroke engines rely on high temperatures to work efficiently, and traditionally, generators have used these.

As we have seen in some of our reviews, synthetic engine oil is highly recommended for use in these motors, as it does not suffer from the problem of increased viscosity.

Synthetic oil is a consistent product in another way; its price does not depend on that of a barrel of crude. While it may be more expensive by the bottle, its properties mean it lasts longer than traditional motor oil. In the long run, this may save you money.

Of course, better performing oil means a better performing generator. This means less fuel, which again is a consideration. Over time, synthetic oil will look after your motor very well. As well as avoiding stalls and jams, this may mean you never have to buy a new generator.

It may not be top of everyone's list, but there are also environmental considerations when burning fossil fuel. Apart from anything else, it'll run out one day.

Final Note

As technology marches on, so we are presented with ever more choice. This is just as true with generator oil as anything else mechanical. Just to drive the point home, engine oil is part of your engine.

Advancing technology means that synthetic oils are getting cheaper, so are more able to compete with the old type in terms of the bottom line.

For such an inexpensive product, it is well worth thinking about what you are actually buying. For a lot of people, engine oil is an afterthought; thought about after fuel, etc. until their generator stops working.

We hope our guide to the best oils for generators helps you to make your choice.

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