Best Oils for Generators: Increase Engine Efficiency & Life

Generators are useful machines that keep your appliances and tools running during a power outage. Also, portable units make your camping and tailgating the most memorable ones. But owning a generator is not enough; you must have to maintain it regularly to increase its life.

The engine is the most critical part of any generator. Without oil, the engine doesn’t work. Therefore, it is essential to use the right oil according to your generator type and do frequent oiling to protect the engine from damages.

But which type of oil is best for your generator? Here we are reviewing the seven best engine oils that you can use in generators.

Generator Oil Reviews





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Castrol 15B5FC-3PK EDGE 0W-40 A3/B4 Motor Oil

  • premium full synthetic oil

  • 4.7 litres/bottle

  • titanium technology

Valvoline SAE 5W-30 Synthetic Blend Motor Oil

  • 0.9 liters/bottle

  • combo of synthetic and conventional base stocks

  • MaxLife technology

Shell Rotella T6 Full Synthetic 5W-40 Diesel Engine Oil

  • Works under any temperature/pressure

  • meets API standards and DFS

  • behaves like a 5 weight thinner oil

Briggs & Stratton 30W Engine Oil 100028

  • 48 fluid ounce bottle

  • ideal for 4-stroke air-cooled engines

  • best for pressure 40F-100F

Honda 08207-10W30 PK2 Motor Oil

  • 32 fluid ounce bottle

  • 10-30 viscosity rating

  • Meets API standards

Shell Rotella T5 15W-40 Diesel Engine Oil

  • synthetic blend technology

  • viscosity rate 10-40

  • Triple Protection Plus technology

Cummins 3265336 Onan SAE 15W-40 Oil

  • 32 fluid ounce bottle

  • viscosity rate 15-40

  • ideal for diesel generators

1. Castrol 15B5FC-3PK EDGE 0W-40 A3/B4 Motor Oil – Top Quality Full Synthetic Oil

Castrol Synthetic motor oil

Size and Weight: Castrol EDGE 0W-40 oil comes in 5-Quart bottle size and weighs 14.9 pounds. Here 5 Quarts are equal to 4.7 liters.

Oil Type: It is a premium full synthetic oil designed to work under extreme pressure and temperature, making it an ideal choice for portable gasoline generators. Synthetic oil contains chemical compounds that are artificially made.

Viscosity and Weight: In the winter season, Castrol 0W-40 flows like 0 weight oil, but after achieving the full operating temperature, it gains the viscosity of a 40 weight engine oil to provide ultimate engine protection.

Titanium Technology: Its titanium technology changes the way oil operates under pressure. You will see a massive difference in the performance of your generator.

Protection: Castrol EDGE 0W-40 offers greater engine protection as compared to conventional engine oils. It lubricates all the moving parts of the engine to reduce friction. No matter how much speed your generator’s engine is running at, it reduces metal-to-metal contact. Moreover, your engine will remain free from deposits, wear, and oxidation. As a result, it will work smoother and give excellent performance and economy.

Certification: This engine oil is fully API (American Petroleum Institute) certified. It meets the SN/CF, ACEA A3, ACEA B3, ACEA B4, and A3/B4 set standards.

These certifications are for seal compatibility, sludge control, wear, treatment, and deposit protection. Also, these certifications ensure that the fuel is formulated to use in small diesel and high-performance gasoline engines.

My Opinion:

Pros: Castrol 0W-40 oil is highly recommended for portable generators. It works well under extreme pressure. It reduces friction and increases the life of the generator engine. Also, it is available at a great price.

Cons: Its big-sized bottle may cause storage problems when traveling with a generator.

2. Valvoline SAE 5W-30 Synthetic Blend Motor Oil – Best 5W-30 Engine Oil

Valvoline Synthetic Blend Motor Oil

 Size and Weight: Valvoline SAE 5W-30 has a bottle size of 1-Quart that is equal to 0.9 liters. Also, its weight is only 1.65 pounds.

Oil Type: It is a mixture of synthetic and conventional base stocks, which makes it perfect for generators with fuel-efficient engines.

Viscosity and Weight: This Valvoline 5W-30 acts like a 5 weight thinner oil in cold weather conditions, and when the temperature rises, it behaves like a 30 weight engine oil.

Protection: For ultimate protection of your generator’s engine, this Valvoline oil is a perfect choice. Its seal conditioning property gives new life to old engine seals. Not only this, but it also has anti-wear additives that protect the engine from damages. These additives create a thick layer of anti-wear for engine protection. 

MaxLife Technology: This synthetic blend generator oil is powered by MaxLife technology. It helps keep the engine free from oxidation. You will never find any deposit formation and sludge after using this oil. 

My Opinion:

Pros: Valvoline SAE 5w-30 is designed to meet the needs of fuel-efficient engines. It prevents and stops oil leakage, protects the engine from wear and deposits, and increases the engine’s life.

Cons: If you have a severely worn engine, it will not improve its performance.

3. Shell Rotella T6 Full Synthetic 5W-40 Diesel Engine Oil – Best 5W-40 Engine Oil

Shell T6 Synthetic Diesel Engine Oil

Size and Weight: Its 1-gallon bottle weighs 23.7 pounds.

Oil Type: This diesel engine oil is also fully synthetic, like the Castrol 0W-40 oil. It works great under any temperature and pressure.

Viscosity and Weight: Shell Rotella 5W-40 behaves like a 5 weight thinner oil in winter for easy starts. But as the operating temperature goes up, its viscosity changes and converts it into a 40 weight engine oil.

Protection: It offers extreme quality protection to your engine from wear and sludge. Shell Rotella T6 helps generator engines to improve their economy. It maintains the engine oil pressure and opposes viscosity loss.

Additive Technology: It includes an additive technology that helps prevent damages caused by dirt and contaminants.

Certification: Rotella T6 meets and exceeds the API standards and DFS (Detroit Fluid Specifications).

My Opinion:

Pros: Shell Rotella T6 works extremely well under higher temperatures. It is an expensive product that works best with diesel engines. Also, it ensures fuel economy and protects the engine from sludge and wear.

Cons: There is no clear window to tell how much oil is left.

4. Briggs & Stratton 30W Engine Oil 100028 – Briggs & Stratton Engine Oil

B&S engine oil

Size and Weight: This Briggs & Stratton 30W engine oil comes in a 48 fluid ounce bottle that weighs 2.63 pounds.

Oil Type: It is a high-quality detergent oil, ideal for 4-stroke air-cooled engines. You can use it on any Briggs & Stratton generator or a unit that supports SAE 30W oil.

Viscosity: Briggs & Stratton SAE 30W is a single viscosity oil with a viscosity rating of 30.

Higher Temperatures: It is designed to work well under higher temperatures anywhere between 40F and 100F.

Protection: It protects the engine by preventing deposit formation and allows it to run smoothly.

Certification: This SAE 30W oil from Briggs & Stratton is SJ/CD classified by the American Petroleum Institute).

My Opinion:

Pros: Briggs & Stratton 30W engine oil offers excellent lubrication and engine protection. It is manufactured in the USA and available at a moderate price. Also, it works well at higher temperatures.

Cons: You have to check the oil level on a regular basis.

5. Honda 08207-10W30 PK2 Motor Oil – Generator Oil for Honda

Honda motor oil

Size and Weight: Its 32 fluid ounce bottle weighs 3.84 pounds.

Oil Type: It is a synthetic blend engine oil that works great in all weather conditions. If you have a gasoline-powered Honda generator, this oil is made for you.

Viscosity and Weight: Honda 10W-30 has a viscosity rating of 10 at low temperatures and 30 viscosity rating at higher temperatures.

Protection: Your generator engine will remain protected from varnish, wear, and corrosion.

Certification: It meets and exceeds all API service classifications.

My Opinion:

Pros: Honda 10W30 is a synthetic blend engine oil made for gasoline engines. Its viscosity rating is on the higher side, but it performs well in all weather conditions.

Cons: It is expensive oil.

6. Shell Rotella T5 15W-40 Diesel Engine Oil – Best 15W-40 Engine Oil

Shell Heavy Duty Diesel Engine Oil

Size and Weight: Shell Rotella T5 comes in a 1-gallon bottle weighing 7.68 pounds.

Oil Type: It is a synthetic blend oil, designed to treat diesel engines.

Viscosity and Weight: Shell 15W-40 operates like a 15 weight engine oil when the temperature is freezing. And when the operating temperature goes up, its viscosity changes to 40. 

Synthetic Blend Technology: The synthetic blend technology works extremely well to provide better wear protection. 

Advanced low-ash Formulation: Rotella T5 protects the particulate filters and exhaust catalysts to maintain generator emission compliance. 

Protection: It protects and extends the engine life and maintains its viscosity no matter whatever the temperature is. Its Triple Protection Plus technology provides excellent protection against deposits and oil breakdown.

Certification: According to API, this oil is classified as CK-4 as it maintains high temp/high shear viscosity.

My Opinion:

Pros: Shell Rotella T5 is one of the best oil made for diesel engines. It prevents oil breakdown and offers triple protection against deposits and wear. Also, it is cheaper than most of the 15W-40 options. 

Cons: It comes in a big size bottle.

7. Cummins 3265336 Onan SAE 15W-40 Oil – Perfect for Efficiency

Cummins best generator oil

Size and Weight: With 32 fluid ounce bottle size, its weight is 1.93 pounds. 

Oil Type: It is a thick oil made for powerful diesel engines. Along with portable diesel generators, you can also use it in your RV generator.

Viscosity and Weight: Cummins SAE 15W-40 has a viscosity rating of 15 in winters. It changes to 40 when it reaches to maximum operating temperature.

Protection: It prevents oxidation to keep the engine in good working condition. Also, it offers better fuel economy and protects it from wear and tear.

Certification: There is no clear information about the certifications of this oil, but it fully meets Cummins’ standards and expectations.

My Opinion:

Pros: Cummins 3265336 is made for diesel-powered generators with higher power output. It prevents oxidation better than many thinner oils. Also, it can be used on RV generators. 

Cons: It is not an ideal choice for winters.

Buyer’s Guide

Engine oil plays a vital role in increasing the performance and lifespan of your generator. So, it must not be selected in a hurry. You have to consider a few basic things before the purchase to get the best possible oil for your power-generating machine.

Follow the User Guide

First, go through the user manual of your generator to know what type of oil the manufacturer is recommending to you. If you don’t have a user manual, then it becomes necessary to know about the types of oil and their properties and the type of generator you have, to buy the right oil for your engine.

Types of Oil

There are three basic types of engine oil.

Full Synthetic Oil: For high-performing generator engines, this type of oil is the best choice. It not only protects the engine from sludge and thermal breakdown but also resists oxidation and offers higher levels of viscosity. You will not need to change the oil regularly, but its price is higher than the blended and conventional ones.

Synthetic Blend Oil: It is a blend of fully synthetic and conventional base oil. It contains many properties of full synthetic oil, but its price is on the lower side.

Conventional Oil: It is the most common type of oil that can be used in low-power generator engines.

Knowing the Oil Properties

It is necessary for you to know about the SAE (Society of Automotive Engineers) rating system. This rating is followed by two numbers. If we take the example of SAE 5W-40, then here W is referred to as winter, and 5 is the viscosity. It means the oil has a 5 viscosity rating at cold temperatures, and when it reaches the full operating temperature that is 100 degrees Celsius, its viscosity rating changes to 40.

Type of Generator

Your generator type will also help you to find the right oil for your engine. Generators with air-cooled engines need 10W-30 engine oil for temperatures more than 20F. You can use this oil in all mid-power and high-powered generators ranging from 7-Kilo-watt to 15-Kilo-watt. And for below 20F temperatures, it is suggested to use 5W-20 and 5W-30 engine oils.

On the other hand, liquid-cooled generators require 15W-40 oil.

What are the benefits of using engine oil?

  • You cannot operate your generator’s engine without adding oil to it. Big-sized generators with higher power output come with high-performance engines that generate more heat than the smaller engines. So, the oil that can withstand higher temperatures provides sufficient protection to your engine.
  • Engine oil creates and maintains a thin barrier between the engine moving parts to keep them protected from damages.
  • It also protects the engine from mineral deposits. The impurities that develop due to the fuel/air mixture burning affect the engine’s efficiency. The detergents present in good quality engine oils catch those contaminants and remove them through the oil filter.
  • Engine oils also protect against oxidation. The water vapors present in oxygen start rusting the engine metal parts. Here, the engine oil works effectively to create a thin layer of protection to stop water from getting in contact with metal.

How much oil my generator can consume?

Oil consumption depends on various factors; therefore, it is hard to calculate the amount of oil your generator can consume. These factors include the model of your generator, the load applied, engine runtime, and other factors. Therefore, it is suggested to keep checking the oil level and its viscosity from time to time.

What will happen if I add too much or too little oil to my generator?

Both scenarios will affect the engine in a bad way. Too little oil will give a shorter runtime and activate the low-oil warning system. In addition, running your generator when the oil level is too low can burn the engine. On the other hand, too much oil can increase the resistance of the engine. Also, you may experience oil leakage from the air cleaner.

2 thoughts on “Best Oils for Generators: Increase Engine Efficiency & Life”

  1. I have seen some youtube videos showing the use of Rotella 15W-40 Diesel engine oil on Gasoline powered Generators like the Predator 3500 with a 212cc engine from Harbor Freight.
    Is this correct ? Is it better ?
    I have my own a Westinghouse WH 2400i gasoline powered generator that uses 15W-40 but it is specified on the owners manual, the Predator shows 10w-30 on the manual.

  2. Yes, it is correct. You can use Shell Rotella T6 15W-40 diesel engine oil on a gasoline-powered generator. It is better in the sense that diesel oil has more detergents so it will clean the dirty motor internally, well.
    What is written in the manual, you have to obey it to keep your generator running for long.


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