Can You Use 15W40 Diesel Oil in a Gas Engine? Get The Facts!

If it’s a case where your engine is gas, then you may be wondering if 15w40 diesel oil can be used in it. This question can be tricky since finding an oil suitable for gas engines can be challenging.

However, we don’t think it is a good idea to use diesel oil in any gas engine. The reason for this is because it tend to have a higher thickness and more viscosity when compared to engine oils.

Overview of 15w40 Diesel Oil

Diesel oil such as 15W40 is an engine oil suitable for diesel engines. Generally it is thicker than regular engine oils, diesel oil helps protect engines against high heat produced by these machines.

15W40 is often used in farm tractors and other heavy-duty equipment. It has been designed to offer excellent protection against wear, deposits, oxidation, and nitration.

Diesel oil not only provides superior lubrication, but it also reduces carbon monoxide emissions and boosts fuel economy. As such, it has become a go-to choice for owners of gas-powered vehicles that have been converted to run on diesel fuel.

Many drivers of modified cars and trucks opt for diesel oil, believing it to be tougher than gasoline motor oil and better able to withstand higher temperatures generated by turbocharged engines.

However, 15W-40 motor oil may not be suitable for all vehicles. Some may require regular 5W-30 instead of 15W-40, so it’s essential to know your car and its specifications before using any oil.

Uses of 15W40 Diesel Oil

Can You Use 15W40 Diesel Oil in a Gas Engine

There are many reasons why someone might opt to use diesel oil in their gas engine. Some favor its increased detergency, while others require a higher viscosity for better protection against wear and tear.

However, if you plan to use diesel oil in a gasoline engine, it must meet certain specifications and viscosity requirements. Otherwise, the oil could potentially cause engine damage.

Additionally, 15w40 diesel oil must be pumpable at low temperatures – an essential consideration when using it in your gas engine.

15w40 oil is a heavy-duty fleet motor oil designed to offer additional protection for over-the-road trucks, farm tractors and off-highway vehicles that use Compressed Natural Gas (CNG) or Liquefied Natural Gas (LNG). It boasts excellent oxidation stability as well as superior corrosion and sludge protection in various operating conditions.

Can You Use 15w40 Diesel Oil in a Gas Engine?

Diesel oil contains more detergents and additives than gasoline motor oils, making it difficult for gas engines to handle. This could negatively impact your vehicle’s performance.

However, there are actually some fleet type diesel oil that is dual rated for gasoline and diesel which can be used in gasoline engines. Unfortunately, these dual-rated oils tend to be of older generation and may not be compatible with modern fuel systems.

Modified gasoline engines often require a high viscosity oil to help them handle the additional pressure created by turbocharging or other modifications. Diesel oils tend to be easier to locate in these viscosities and may be an ideal choice in cases like these.

Are 15w40 and 15w30 Diesel Engine Oils the Same?

The short answer is no, 15W40 and 15W30 diesel engine oils are not the same. They tend to hwve different viscosity levels. The 15W40 is considered to be thicker than the 15W30. The good news is that if you have a diesel engine vehicle, it is a possibility that you can use both oils.


The only way we recommend using diesel oils in gasoline engine is if it’s a case where your engine is compatible to use both regular motor oil and high viscosity diesel oil. Otherwise, we think it would be best if you refrain from using diesel oil in gas engine as it can lead to engine failure which can be costly.