Some customers may favor diesel oil over gasoline oil for a number of reasons:
- Diesel oil is perceived as more “heavy-duty” than gasoline oil.
- Some customers desire a higher viscosity, and it may be easier to find a 5W-40 or 15W-40 diesel oil than gasoline oil.
- Diesel oil typically contains more robust detergency additives than gasoline oil.
It is safe to use a diesel oil in your gasoline engine, provided it meets the appropriate specifications and viscosity requirements of the engine. For example, if your gas engine calls for a motor oil that meets the API SN specification, you can safely use a diesel oil of the correct viscosity that meets the API SN spec. For the typical gasoline application, however, a diesel oil isn’t required and the more appropriate choice is a quality gasoline motor oil for both performance and value.
Pay Attention to Oil Specifications
The American Petroleum Institute (API) publishes its “C” category of specifications for diesel oil currently CK-4) and its “S” category for gasoline motor oil (currently SN). It’s common for today’s diesel oils to carry both the API CK-4 and API SN specifications. Though they’re truly designed for diesel applications, they can be used in gasoline applications for motorists who want to use one oil in all applications. If the diesel oil carries both specs, the oil is safe to use in diesel and gasoline applications. If the diesel oil does not carry the “S” category, AMSOIL strongly recommends against using it in gasoline applications.
The Correct Oil Formulation for the Application
In the past, motorists may have heard diesel oils were tougher than gasoline oils for a number of reasons, including higher viscosity, improved corrosion protection, higher Total Base Number and more. Diesel oils are often thought to be formulated with special components not available in gasoline oils, such as more robust detergency additives to handle the soot inherent to diesel engines. In some motorists’ minds, diesel oils are still analogous to better protection. While that may have been true in the past, modern oils are formulated for their intended applications. While both diesel and gasoline oils contain many of the same additives to guard against wear, corrosion, foaming and more, they also contain additives designed to manage the byproducts of combustion. Some of those byproducts change, depending on whether the engine runs on gasoline or diesel fuel. If your vehicle uses a gasoline engine, it’s best to use an oil that contains the correct additives to handle the byproducts of gasoline combustion. The same holds true if you’re operating a diesel engine.
When to Favor Diesel Oil Over Gasoline Motor Oil
While some enthusiasts believe using diesel oil can be beneficial in heavily modified gasoline engines, we have them covered with premium synthetic motor oils that are specially engineered for these applications, including Z-ROD® Synthetic Motor Oil and DOMINATOR® Synthetic Racing Oil. The only time diesel oil should be favored over gasoline motor oil is when you’re dealing with a mixed fleet. Examples of mixed fleets include someone with a diesel-powered RV with a gas-powered generator onboard who wants one oil for both engines, or a contractor with a gasoline-powered pickup and dieselpowered equipment. A diesel oil that meets all the appropriate specifications and viscosity requirements would likely be your best bet.
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