Synthetic Diesel Oil Frequently Asked Questions

AMSOIL is not a mass-market brand. We are a brand for enthusiasts, with strong brand loyalty among millions of enthusiasts who are aware of the AMSOIL brand. Enthusiasts are passionate about their vehicles and are willing to pay a premium for high-performance products.

We make significant investments in the AMSOIL brand as the official oil sponsor of the Diesel Power Challenge and the Ultimate Callout Challenge, raising brand awareness with turbodiesel pickup enthusiasts.

Shell and Mobil are well-respected brands that make good products; however, AMSOIL builds more protection into its products that goes far beyond the industry and OEM specifications. Signature Series Max-Duty Synthetic Diesel Oil delivers up to 6X more wear protection than required by the Detroit Diesel DD13 scuffing test.

For over 50 years, our focus on protection has helped us earn the trust of serious enthusiasts and people who depend on diesel power to make a living.

YES. Using AMSOIL synthetic diesel oil has no effect on vehicle warranties. A federal law in the United States called the Magnuson-Moss Act (1975) prevents original equipment manufacturers from putting conditions on vehicle warranties attached to any product or service identified by brand, trade or corporate name, unless the manufacturer provides that product or service free of charge.

The law in Canada states that an OEM cannot require a consumer to use its parts/oil under the threat of voiding the warranty. This practice is referred to as “tied selling” and is in direct violation of the Canadian Competition Act due to its anti-competitive nature.

The Consumer Protection Acts in each province are the Canadian equivalent to the Magnuson-Moss Warranty Act. The law varies by province.

This means consumers have the freedom to use aftermarket products of their choice without fear of losing the original limited or implied vehicle warranty. For additional information, visit www.amsoil.com/warrantysecure, or contact the AMSOIL Technical Department at (715) 399-TECH (8324) or tech@amsoil.com.

No. Extending oil change intervals will not void new vehicle warranties. To affect the vehicle warranty, it must be determined that the lubricant was directly responsible for the failure; if the oil didn’t cause the problem, the warranty cannot be voided, regardless of brand or length of time in use. For additional information, visit www.amsoil.com/warrantysecure, or contact the AMSOIL Technical Department at (715) 399-TECH (8324) or tech@amsoil.com.

No. Heavy-Duty Protection is the overarching message that defines how AMSOIL Heavy-Duty Synthetic Diesel Oil goes beyond minimum requirements, keeping equipment protected with 4X better engine wear protection than required by a leading OEM. Heavy-Duty Protection can refer to the semi-truck hauling goods across the country, or a contractor working on the job site. AMSOIL Heavy-Duty Synthetic 5W-40, in particular, is specifically designed for the demands that many serious turbo truck enthusiasts put their diesel trucks through.

Both products exceed the latest API CK-4 specification. AMSOIL Heavy-Duty Synthetic Diesel Oil keeps equipment protected with 4X better wear protection than required by the Detroit Diesel DD13 scuffing test. For even greater protection, AMSOIL Signature Series Max-Duty Synthetic Diesel Oil provides 6X more wear protection than required by the test. Signature Series is engineered for hardcore enthusiasts and fleet owners interested in the best oil for their diesel engines, with reserve protection that allows them to extend their drain intervals.

AMSOIL delivers improved profitability. We protect critical components better than the competition through higher-quality, longer-lasting synthetic lubricants. We lower maintenance costs, reduce equipment failures and extend lubricant change intervals, further decreasing costs.

YES. The combination of low oil volatility and clean operation effectively reduces oil consumption and emissions. AMSOIL diesel oils are thermally stable with strong resistance to high-temperature volatility (burn-off) compared to conventional petroleum-based diesel oils.

YES. AMSOIL Max-Duty and Heavy-Duty Synthetic Diesel Oils are both recommended for diesel applications calling for the API CK-4 specification.

Our philosophy has always been to set a target for quality and formulate products that meet that target.
The API licensing system is a voluntary certification that only sets minimum quality standards. Because it is a standard, licensing limits the flexibility AMSOIL needs to quickly adopt new technologies that can improve protection. Our research indicates many diesel enthusiasts and people who depend on their diesel to make a living focus more on protection than on the API doughnut. We are in that camp.
That is why AMSOIL uses specifications like CK-4 as the minimum and engineer protection into our products that goes beyond API standards. We want to give customers the most protection we can, and sometimes that requires opting out of a licensing program. Diesel customers can rest assured their equipment is protected, and we back them up with our warranty.

YES. AMSOIL Max-Duty and Heavy Duty Synthetic Diesel Oils are formulated with lower sulfur content to be compatible with today's high-speed, four-stroke diesel engines with exhaust after-treatment systems, and they also exceed previous diesel oil specifications. They are suitable for use in older diesel engines calling for API CJ-4, CI-4 Plus, and CF oils.

No. Synthetic oils do not cause engines to leak. AMSOIL Signature Series Max-Duty Synthetic Diesel Oil and AMSOIL Heavy-Duty Synthetic Diesel Oil are fully compatible with modern seal materials and are properly formulated to condition seals, keeping them pliable to prevent leakage. Some early synthetic motor oils were made with materials that were harder on seals, but today’s synthetic oils have come a long way. Synthetic oil is perfectly safe for use in both new and high-mileage engines.

Each vehicle manufacturer defines "normal" and "severe" driving conditions for its equipment; AMSOIL recommends owners check these definitions in their owner’s manual to determine the service condition in which they typically drive.

AMSOIL defines normal service as personal vehicles frequently traveling greater than 10 miles (16 km) at a time and not operating under severe service.

AMSOIL defines severe service for gasoline engines as turbo/supercharged engines, commercial or fleet vehicles, excessive idling, first-time use of AMSOIL synthetic motor oil in vehicles with over 100,000 miles without prior continuous use of AMSOIL synthetic motor oil, daily short-trip driving less than 10 miles (16 km), frequent towing, plowing, hauling or dusty-condition driving.

AMSOIL defines severe service for diesel engines as extensive engine idling, daily short-trip driving less than 10 miles (16km) or frequent dusty-condition driving.

See the AMSOIL Product Recommendation and Drain Interval Chart for additional information.

No. You can use whichever brand of filter you choose and AMSOIL synthetic motor oils will still be guaranteed to protect your vehicle for the advertised period. However, you will need to change your oil filter according to the filter manufacturer’s recommendations and top off the oil.

Yes. It is normal for vehicles to use some motor oil. AMSOIL recommends checking your oil level every time you fill your fuel tank.

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 specification for diesel oil (currently CJ-4) and its “S” category for gasoline motor oil (currently SN). It’s common for today’s diesel engine oils to carry both the API CJ-4 and SN specifications. Though they’re truly designed for diesel applications, they can be used in gasoline applications for those who want to use one oil in all applications. If the diesel oil carries both specs, feel assured the oil is safe to use in diesel and gas applications. If the diesel oil does not carry the “S” category, it is not recommended to use it in gasoline applications.

YES. AMSOIL Signature Series Max-Duty Synthetic Diesel Oil is suitable for use in applications specifying API SN+ and earlier specifications, making it ideal for mixed-fleet use. In particular, AMSOIL Signature Series 5W-30 is a premium all-fleet oil engineered for modern diesel and gasoline engines.

AMSOIL Commercial-Grade products provide a combination of value and price point; they are specially engineered for commercial equipment at the best price. AMSOIL Commercial-Grade Diesel Oil offers 2X better engine wear protection than required by a leading OEM.

More synthetic base-oil content means more protection. Some synthetic-blend oils have as little as 1% synthetic content and can still be considered a synthetic blend. Our research reveals that current API-licensed synthetic-blend diesel oils contain between 1-15% maximum synthetic content. The extra synthetic base oil in our synthetic-blend formula helps deliver better wear protection, lower oil consumption, better viscosity control and better extreme-temperature performance.