AMSOIL SIGNATURE SERIES 15W-40 100% SYNTHETIC MAX-DUTY DIESEL OIL

AMSOIL Signature Series 15W-40 100% Synthetic Max-Duty Diesel Oil is a top-tier synthetic diesel oil built to protect hard-working engines in pickup trucks, heavy-duty rigs, and off-road equipment while confidently extending drain intervals well beyond conventional oil change schedules.

Modern diesel engines operate under extreme stress. Turbochargers spin at high RPM under heavy boost, exhaust gas recirculation systems push soot levels higher, and towing or hauling loads generate sustained high temperatures that punish conventional oils. A 15W-40 diesel oil that can't handle these demands will shear down, thicken with soot, and leave critical components vulnerable to accelerated wear and deposit formation.

6X MORE WEAR PROTECTION THAN THE DETROIT DIESEL STANDARD
Third-party testing in the Detroit Diesel DD13 Scuffing Test for specification DFS 93K222 shows Signature Series Max-Duty delivers 6X more wear protection than the standard requires. That test is specifically designed to evaluate an oil's ability to protect rings and cylinder liners from scuffing under extreme-pressure conditions. In side-by-side testing against a leading conventional 15W-40, AMSOIL kept cylinder liners looking like new, while the competing brand produced severely scuffed liners. Ring and liner wear is the primary driver of compression loss, oil consumption, and reduced horsepower over time. This level of protection matters in engines like the Cummins 6.7L, Duramax 6.6L, and Power Stroke 6.7L that owners expect to run for hundreds of thousands of miles.

UP TO 60% BETTER TURBO CLEANLINESS
Carbon deposits on turbocharger components restrict airflow, reduce boost efficiency, and can eventually cause bearing failure. Signature Series delivers up to 60% better turbo cleanliness based on specification standards of the CAT C13 2nd Ring Top Land Carbon test. It also provides 40% less carbon accumulation, which directly benefits turbodiesel pickup owners who tow heavy fifth wheels or flatbeds, as well as anyone running aftermarket tunes that increase exhaust gas temperatures and turbo demand.

RESISTS SOOT-DRIVEN VISCOSITY INCREASE
Diesel combustion produces soot, and EGR-equipped engines push even more of it into the oil. Soot particles agglomerate and thicken the oil, increasing drag on internal components and reducing fuel efficiency. Signature Series is formulated with top-tier synthetic base oils and boosted detergent/dispersant additives that keep soot particles suspended independently, preventing them from clumping into larger, wear-causing particles. The result is stable viscosity throughout the drain interval, even under heavy soot loading. In the Caterpillar-1N oil consumption test, Signature Series provides up to 76% less oil consumption than required by the API CK-4 standard, with a measured consumption rate of just 0.12 g/kWh versus the 0.5 g/kWh CK-4 limit.

UP TO 2X BETTER RUST PROTECTION
Diesel engines that sit idle between jobs or experience seasonal downtime are vulnerable to internal corrosion. Moisture condenses on cylinder walls and bearing surfaces, and without adequate corrosion inhibitors, rust pitting can cause lasting damage before the engine even turns over. Signature Series provides up to 2X better rust protection based on industry-standard NMMA FC-W Rust Test results.

EXCELS IN EXTREME TEMPERATURES
Signature Series 15W-40 resists thermal breakdown better than conventional and competing synthetic diesel oils. Unlike conventional 15W-40 oils that contain wax, this 100% synthetic formulation stays fluid in sub-zero temperatures for easier cold starts, faster oil flow at startup, and reduced dry-start wear. The 0W-40 variant (DZF) in the Signature Series Max-Duty lineup offers 4X better cold-cranking ability than a conventional 15W-40 in ASTM D5293 testing. Even the 15W-40 (DME) itself delivers strong cold-weather performance with a CCS viscosity of 4934 cP at -20°C, well within the SAE 15W requirements, making it suitable for a broad range of climates.

SPECIFICATIONS AND COMPATIBILITY
Signature Series 15W-40 (DME) meets or exceeds the following specifications: API CK-4/SN, CJ-4, CI-4+, CF, CF-2, Volvo VDS4.5, VDS4, VDS3, Mack EOS-4.5, EO-O, Renault RLD-4, RLD-3, Cummins CES20086, CES20081, Caterpillar ECF-2, ECF-3, ECF-1-a, DDC 93K218, 93K215, 93K214, DFS 93K222, ACEA E9, E7, MB 228.31, MAN 3575, MTU Type 2.1, Type II, Type I, JASO DH-2, Allison TES439, Deutz DQC III-10LA, Scania LA-2, Chrysler MS 10902, and Ford WSS-M2C171-F1. It is compatible with other conventional and synthetic engine oils. Aftermarket oil additives are not recommended for use with AMSOIL synthetic diesel oils.

SERVICE LIFE
For heavy-duty on-road and off-road diesel applications, Signature Series 15W-40 supports drain intervals up to 3X the OEM recommendation, not to exceed 60,000 miles, 600 hours, or one year, whichever comes first. For turbodiesel pickups like the Ram 2500/3500 Cummins, Ford Super Duty Power Stroke, and Chevrolet/GMC Duramax, it supports 2X the OEM recommendation, not to exceed 25,000 miles or one year. For gasoline engine applications, it supports 2X the OEM recommendation, not to exceed 15,000 miles or one year. Drain intervals may be extended further with oil analysis. Extended drain intervals are not recommended for performance-modified engines or when using biofuels containing more than 10% ethanol or 15% biodiesel (B15).