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Bottom line on using thicker oil or thinner oil

Using a viscosity one grade higher or lower than what’s recommended for your engine likely won’t do lasting harm.

But, to alleviate any concerns about engine protection and your vehicle warranty, it’s best to use the viscosity recommended in your owner’s manual.

If you have questions or concerns, contact AMSOIL Technical Services ( to determine the appropriate viscosity for use.

What is the difference between synthetic and conventional oil?

Answer: Motor oil, whether synthetic or petroleum-based, consists of molecular chains of hydrogen and carbon atoms, referred to as hydrocarbons. Petroleum crude oil is a thick, highly flammable dark-brown or greenish liquid with high energy density. Many contaminating elements exist in this complex mixture of hydrocarbons, including sulfur, nitrogen, oxygen and metal components such as nickel or vanadium. Petroleum crude oil is the raw material used for a wide variety of petrochemicals, including solvents, fertilizers, plastics and lubricants.

The oil refining process separates the various types of molecules in the oil by weight, resulting in a concentrated batch suitable for manufacturing products such as gasoline, LPG, kerosene or lubricant base oils. The chemical composition of conventional motor oil can vary substantially depending on the raw crude oil refining process.

While petroleum base oils are refined, synthetic base oils are manufactured and can achieve a higher performance level. Synthetic oil is chemically engineered for a certain molecular composition with a tailored and uniform structure. Such fine-tuned control over the final molecular composition of synthetic oils is the key to their superior performance properties. Designing molecular structures in a planned and orderly fashion results in molecules, and end-products, that are far more stable than their refined petroleum counterparts.

Is there a recommended procedure for changing to AMSOIL synthetic motor oil?

Answer: There are no special requirements for changing to AMSOIL synthetic motor oil. However, in older vehicles with high mileage, it may be advisable to use AMSOIL Engine and Transmission Flush first. This will ensure the engine is clean and free of accumulated contaminants that may affect the service life of AMSOIL synthetic motor oil. Installation of an AMSOIL Oil Filter at every oil change is also recommended.

Can AMSOIL lubricants be safely mixed together?

Answer: Applications require specific lubricant properties to deliver maximum performance and protection. AMSOIL carefully tailors its synthetic lubricants under the strictest quality control standards to provide the required properties for the intended application. Mixing AMSOIL synthetic lubricants is not only unnecessary, it may lead to reduced performance and even equipment failure.

Automatic transmission fluids offer a perfect example. Some transmissions require lubricants that contain specific frictional characteristics to reduce, or eliminate, clutch slippage, while other transmissions may require different frictional requirements. Mixing fluids recommended for different performance specifications may lead to a host of problems, including erratic shifting and transmission failure.

In some applications, mixing lubricants may not lead to equipment failure, but it will reduce performance. For example, if AMSOIL Signature Series 5W-30 Synthetic Motor Oil is installed in a vehicle, and its owner adds AMSOIL OE Synthetic 5W-30 Motor Oil to top off the engine if Signature Series isn’t available, the vehicle will continue to operate perfectly; Signature Series and OE Synthetic Motor Oil share a similar chemistry, and formulations of the same viscosity can be safely mixed. However, mixing lubricants will shorten Signature Series' life expectancy and reduce its performance benefits. AMSOIL does not support extended drain intervals where oils have been mixed.

To minimize the risk of performance- and warranty-related issues due to improper mixing, AMSOIL does not recommend mixing AMSOIL synthetic lubricants.

Synthetic Diesel Oil

Can diesel oil safely be use in gas engines?

It depends on the specifications the diesel oil carries and the recommendation of the original equipment manufacturer (OEM). 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 SP).

You can use diesel oil in a gas engine provided the diesel oil meets the appropriate specifications and viscosity requirements of your engine. For example, if your gas engine calls for a 5W-30 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.

Why do diesel engines need specific oil?

Outside of differences in the fuel, the most notable difference between diesel and gas engines is the way each ignites the fuel. Diesel engines compress air in the combustion chamber until the temperature of the air increases enough to ignite the fuel (sprayed into the combustion chamber by the injector). Gasoline engines, on the other hand, use spark plugs that ignite a mixture of fuel and air at just the right time.

Diesel oil is formulated differently than gasoline oil in order to address issues specific to diesel engines, including higher engine temperatures, oxidation rates, soot levels and deposits. Find the best AMSOIL synthetic diesel oil for your application in the Product Lookup. AMSOIL diesel fuel additives also provide benefits designed to keep diesel engines operating at top performance.

How often should you perform a diesel oil change?

Refer to the vehicle owner’s manual for specific oil-change recommendations. AMSOIL synthetic diesel oils may be used beyond the OEM-recommended interval based on the service-life recommendations on the data sheets or with oil analysis. In addition, AMSOIL offers a full line of premium synthetic gear oil and transmission fluid to keep your diesel running at peak performance.

Thicker or Thinner oil
Synthetic vs Conventional
Changing to AMSOIL
Diesel Oil


CKOIL is an independent AMSOIL dealer. We believe in providing the highest quality products.

We provide custom lubrication solutions to all types of customers. From families to race teams, we have the products to help you save time and money. We are always happy to help any way we can. 

We will literally go the extra mile to keep you on track.

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