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AMSOIL Signature Series is our top-tier, premium 100% synthetic motor oil for gasoline engines. It is designed for motorists who want the convenience of a once-a-year oil change combined with maximum engine protection, extreme temperature performance (hot or cold) and fuel efficiency. How good is it you ask? Signature Series is not only the best motor oil we have ever made, it’s also better than any competing motor oil that we have ever tested.

Signature Series is engineered for enthusiasts seeking maximum protection and performance. Precision-formulated with cutting-edge technology and a longstanding devotion to making the world’s best motor oil. The result: engine protection that blows the doors off the highest industry standards.

Advanced engine technology and rigorous demands placed on modern vehicles can challenge motor oil, eventually leading to decreased engine performance and life. Signature Series delivers the ultimate protection against extremes like high-performance driving, off-roading, towing and extended idling. Its boosted protection also lets you drive further between oil changes. Signature Series is for those who want the absolute best engine protection.

Signature Series is formulated to exceed the higher performance requirements of modern engines in everything from family sedans to high-powered sports cars, providing peace of mind that your engine is well-protected, even in severe driving conditions. It's guaranteed up to 25,000 miles, 1 year, or 700 hours of operation - whichever comes first - drain interval under normal (ideal) driving conditions saving you time and money, and reducing waste oil.

Our top-tier AMSOIL Signature Series motor oil offers exceptional protection against harmful deposits, viscosity increase and engine wear in the toughest of operating conditions, helping you maximize the performance and longevity of your vehicle. Its ability to keep engine components clean and protected, despite increased stress, helps modern, sophisticated engine systems operate smoothly and reliably.

Signature Series premium synthetic motor oil resists viscosity increase and is barely challenged by the industry standard testing. Even when the length of the test was doubled, it delivered twice the viscosity control required by the standard. It is formulated with better base oils and more robust additives than most of our leading competitors. This helps it better fight against Oil Volatility, which helps reduce oil consumption and keep valves clean.

We formulated it to deliver next-level wear protection. In the API Sequence IV-A Engine Wear Test required for the API SP specification, Signature Series delivered 75 percent more wear protection than what is required to pass the test. Its outstanding performance combined with its extended-drain capabilities offer a unique combination of quality and value not offered by other motor oils. Plus their extended-drain capabilities help protect the environment.

➪ Develops a strong fluid film that keeps metal surfaces separated.

➪ Provides 75% more engine protection against horsepower loss and wear. (1)

➪ Provides 50% more cleaning power vs. our AMSOIL OE full synthetic motor oil.

➪ Provides 28% more acid-neutralizing power than Mobil 1. (2) (see image below)

➪ Protects turbochargers 72% better than required by the GM dexos1 Gen 2 specification. (3)

➪ Robust anti-wear additives further reduce wear in metal-to-metal contact regions for maximum engine life.

➪ Guaranteed protection for up to 25,000 miles (40,200 km), 1 year, or 700 hours of operation.

➪ Trusted by top certified mechanics, technicians, and professional engine builders.

(1) Based on independent testing of AMSOIL Signature Series 0W-20 using the ASTM D6891 standard test.

(2) Based upon independent testing of Mobil 1 Annual Protection Full Synthetic 5W-30 and AMSOIL Signature Series 5W-30 in ASTM D2896.

(3) Based on independent testing of AMSOIL Signature Series 5W-30 in the GM turbo coking test.

Most engine wear (75%) occurs at startup. That’s primarily because oils thicken as the temperature drops. Cold oil doesn’t flow as fast and, in some cases, may not be able to flow through tiny oil passages at all. When that happens, engine components are forced to operate without lubrication until the engine warms up the oil enough for it to flow, greatly accelerating wear. For those reasons, cold-flow capability is a critical measure of motor oil performance.

We hired an independent third-party lab to put Signature Series in head-to-head testing against other motor oil brands. Signature Series provided better cold-flow performance than all the other motor oils tested, providing up to 38% better cold cranking viscosity than Royal Purple. The test definitively proved that AMSOIL provides better cold cranking viscosity, helping improve wear protection for engine components at startup. (1) (see image below)

(1) Based on independent third-party testing in the industry-standard ASTM D5293 Cold Crank Simulator test as required by SAE J300.

Dirty or worn components work poorly and don’t last. They cause system failures in engines that dramatically increase maintenance costs. Clean and protected engine components require less maintenance, produce more horsepower, are more fuel efficient and help increase engine life.

Signature Series develops a strong fluid film that keeps metal surfaces separated. Its advanced anti-wear additives further reduce wear in metal-to-metal contact regions for maximum engine life. In the Sequence IVA Engine Test (see image below), it provided 75% more engine protection against horsepower loss and wear than required by the industry standard, extending the life of vital components like pistons and cams. (1)

The Sequence IVA Engine Test, which must be passed to meet the API SN PLUS, SP, or the new 2026 SQ specifications, simulates extended periods of stop-and-go driving. For 100 hours, the test engine cycles between 50 minutes of idling and 10 minutes of elevated rpm – conditions that encourage engine wear. The camshaft is then measured for wear in 84 locations and an average score is determined.

(1) Based on independent testing of AMSOIL Signature Series 0W-20, in ASTM D6891 as required by the API SN specification.

In another test, an independent third-party lab compared Signature Series against a leading competitor in a 100,000-mile test. Signature Series provided far superior wear protection compared to the competition, keeping bearings looking like new after the 100,000-mile test. (1) (see image below)

(1) Testing conducted in an independent lab using Signature Series 5W-30 and a leading synthetic-blend 5W-30 motor oil in Ford F-150 trucks with 3.5L twin-turbo engines.

Do you drive in hot temperatures? Engine sludge is the result of a series of chemical reactions that cause oil to degrade. These reactions are driven by exposure to oxygen and elevated temperatures. The higher the temperature, the more rapid the rate of degradation. In fact, every 18°F (10°C) increase in operating temperature doubles the rate of oxidation.

The byproducts of this reaction form highly reactive compounds that further degrade the lubricant. These byproducts react with other contaminants, forming organic acids and high-molecular-weight polymeric products. These products further react, forming the insoluble product known as sludge. What begins as a thin film of lacquer or varnish builds up on hot or cold metal surfaces and bakes into an expensive mess.

➪ Fortified with a heavy treatment of detergent additives, delivering 28% more acid-neutralizing power than Mobil 1, helping engines stay cleaner longer.

➪ 50% more detergents vs. our OE Series full synthetic motor oil to help keep oil passages clean and promote oil circulation.

➪ Better controls extreme heat and minimizes performance-robbing deposits.

➪ Superior thermal durability that resists breakdown and keeps pistons clean.

➪ Provides 90% better protection against sludge. (1) (see image below)

(1) Based on independent testing of AMSOIL Signature Series 5W-30 in the ASTM D6593 engine test for oil screen plugging as required by the API SN specification.

We formulated Signature Series motor oil with superior thermal durability that resists breakdown and keeps pistons clean. The Sequence IIIH Test uses the Chrysler 3.6L Pentastar engine to evaluate a motor oil’s ability to resist heat and keep pistons clean. The 90-hour test is conducted with motor oil temperatures of 304°F (151°C), much hotter than normal operation, to accelerate oil thickening (viscosity increase) and deposits accumulation.

The intent is to screen oils for their ability to maintain protection under the severe conditions today’s smaller, hotter-running turbocharged engines present. Simply put, it’s designed to push the oil to its breaking point and separate the motor oils that can protect from those that can’t.

AMSOIL Signature Series was barely challenged by the industry-standard testing, demonstrating only a 0.1% viscosity increase. Even when the test length was doubled, Signature Series delivered twice the viscosity control required by the standard. (1) (see image below)

(1) Based on independent testing of Signature Series 5W-30 in the Sequence IIIH Engine Test (ASTM D8111), required by the ILSAC GF-6 and API SP specifications.

In addition, after doubling the length of the Sequence IIIH Test, it delivered 40% cleaner pistons than required by the standard. (1) (see image below)

(1) Based on independent testing of Signature Series 5W-30 in the Sequence IIIH Engine Test (ASTM D8111), required by the ILSAC GF-6 and API SP specs.

How did our Signature Series motor oil achieve such impressive results? We first start with the very best synthetic base oils available, which naturally resist chemical break down in the presence of extreme heat. We then add a finely tuned, high-quality additive package designed to complement and enhance the base oils’ performance. Increased levels of highly active detergent and dispersant additives control contaminants and keep engine parts clean.

The premium base oils combined with the right balance of anti-oxidant additives also control viscosity, helping the oil stay "in grade" despite prolonged exposure to brutal heat. This adds up to premium engine protection in today’s demanding engines. Signature Series protects vital components against wear in the toughest conditions, providing motorists peace of mind and giving them the confidence to extend drain intervals if they choose.

When a competitor’s oil easily passes an industry-standard test, they often reformulate to reduce cost and performance to where it barely passes the test.

When our Signature Series motor oil passes a test (even a double-length test), we continue to search for ways to increase protection even more because, for our customers, 'good enough' just doesn’t cut it. Our goal is to provide enthusiasts the absolute best motor oil on the market, and our team gets excited about the testing to prove it. It’s not easy to impress the professionals that test motor oil for a living, but Signature Series delivered.

Does your vehicle have a turbocharger? The tremendous heat and stress turbos create can cause some oils to break down and form harmful bearing deposits through a process known as "turbo coking". Over time, turbos can suffer reduced performance or fail altogether.

We challenged AMSOIL Signature Series to the GM Turbo Coking Test, which consists of 2,000 cycles of extreme heat soaks. An oil must limit the temperature change within the turbocharger to 13% or less to pass the test. Signature Series provides 72% better turbocharger protection than required by the GM dexos1 Gen 2 specification. (1) (see image below)

(1) Based on independent testing of AMSOIL Signature Series 5W-30 in the GM turbo coking test.

Do you have long commutes? Do you rack up the miles on your vehicle? Signature Series provides reserve protection, allowing you to go longer between oil drains if you so choose. Our proprietary synthetic formulation and long-drain additive system are inherently stable to resist oxidation and neutralize acids over longer periods. Signature Series is designed to deliver outstanding engine protection, cleanliness and performance over extended drain intervals.

Signature Series keeps engines cleaner, longer. It is fortified with a heavy treatment of detergent additives, delivering 28% more acid-neutralizing power than Mobil 1, helping engines stay cleaner, longer. (1) (see image below)

(1) Based upon independent testing of Mobil 1 Annual Protection Full Synthetic 5W-30 and AMSOIL Signature Series 5W-30 in ASTM D2896.

LSPI (Low Speed Pre-Ignition) is the spontaneous ignition of the fuel/air mixture prior to spark-triggered ignition. It occurs in today’s advanced engines and is much more destructive than typical pre-ignition. A properly formulated motor oil is critical for protecting your engine.

Signature Series 100% synthetic motor oil is armed with an advanced detergent system that protects against harmful deposits and low speed pre-ignition (LSPI). Engines equipped with gasoline direct injection (GDi) combined and a turbocharger (T-GDi) provide boosted power and fuel economy. But when these technologies are combined with poorly formulated motor oil, LSPI can become a real threat for the engine.

Car manufacturers like GM have addressed the issue by designing tests to determine a motor oil’s ability to prevent LSPI. Signature Series achieved 100% protection against LSPI in the engine test required by the GM dexos1 Gen 2 spec. - zero occurrences were recorded throughout five consecutive tests. (1)

(1) Based on zero LSPI events in five consecutive tests of Signature Series, XL and OE 5W-30 Motor Oil in the LSPI engine test required by the GM dexos1 Gen 2 spec.

Signature Series motor oil fights against viscosity breakdown better than the competition providing superior protection of pistons, cams, and bearings.

Signature Series fights oil volatility 38% better than Mobil 1 and 17% better than Royal Purple, helping reduce oil consumption and keep valves clean.

For additional information, please check out our AMSOIL Signature Series Data Bulletin (PDF). __ | __ SHOP NOW !