AMSOIL Signature Series 15W-40 100% Synthetic Max-Duty Diesel Oil
Developed to protect the horsepower diesel enthusiasts crave and extend the life of hard-working commercial equipment in the most severe conditions. Signature Series synthetic technology delivers max-duty protection in on- and off-road applications.
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Product data sheets
View, download, or save a copy of the Product Data Sheet or Safety Data Sheet for AMSOIL Signature Series 15W-40 100% Synthetic Max-Duty Diesel Oil.
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 CK-4/CJ-4 oil engineered for hard-working on-road and off-road diesel engines. Built from synthetic base oils with a boosted detergent and dispersant package, the formula meets API CK-4/SN, CJ-4, CI-4+, CF, and CF-2, plus a long list of Volvo, Mack, Renault, Cummins, Caterpillar, Detroit Diesel, MB, MAN, MTU, and JASO heavy-duty approvals. Signature Series 15W-40 is built for fleet trucks, work pickups, agricultural and construction equipment, and tuned diesels that demand maximum-duty wear, soot, and turbo protection over long drain intervals.
Wear protection in heavy-duty service
Wear on rings and cylinder liners drives oil consumption up and pulls horsepower and fuel economy down. Signature Series Max-Duty delivers 6X more wear protection than required by the Detroit Diesel DD13 Scuffing Test for specification DFS 93K222, based on third-party testing using 5W-30 as a worst-case representation. In comparison testing against a leading conventional 15W-40 in the same DD13 protocol, Signature Series Max-Duty kept cylinder liners looking like new. The Four-Ball Wear Test (ASTM D4172) records a 0.45 mm scar for the 15W-40 grade.
Turbo cleanliness and tune-tolerant protection
Turbocharged diesels punish the oil at the bearing and ring belt, especially when towing heavy loads or running aggressive tunes. Signature Series Max-Duty delivers up to 60 percent better turbo cleanliness, based on specification standards of the CAT C13 2nd Ring Top Land Carbon test, and is built to withstand the extra demand placed on the turbo when the truck is pulling a load or running a horsepower tune.
Soot control and viscosity stability
Top-tier synthetic base oils resist oxidation and the thickening effects of soot contamination, while boosted detergent and dispersant additives keep soot particles suspended and independent. Suspended soot is less likely to agglomerate into the larger wear-causing particles that grind on liners, lifters, and rings. Signature Series 15W-40 holds an HTHS viscosity of 4.5 cP (ASTM D5481) and a NOACK volatility of 5.1 percent (ASTM D5800), so the oil retains its working viscosity through high-temperature service while keeping evaporative oil consumption low.
Cold-start flow and hot-temperature stability
Signature Series Max-Duty resists thermal breakdown better than conventional and competing synthetic diesel oils. Unlike conventional oils, the formula contains no wax and stays fluid in sub-zero temperatures for easier starting, improved oil flow, and reduced cold-start wear. The 15W-40 grade reaches a CCS viscosity of 4,934 cP at -20 C (ASTM D5293) and a pour point of -40 C (ASTM D97), with a viscosity index of 142.
Reduced oil consumption and rust protection
Lower volatility means less evaporative oil consumption, and Signature Series Max-Duty delivers up to 76 percent less oil consumption than required by the API CK-4 standard in the Caterpillar 1N oil consumption test. The same formula provides up to 2X better rust protection in the NMMA FC-W rust test, important for equipment that sits seasonally or operates in humid and corrosive environments.
Recommended applications and service guidance
Use the live AMSOIL product page and your owner's manual to confirm the current viscosity, API category, OEM approvals, and service guidance for your engine before ordering. AMSOIL updates approvals and recommendations as formulas and manufacturer requirements change.
For extended service, follow the current AMSOIL guidance, your equipment manual, and oil-analysis results. Extended intervals are not appropriate for every engine or operating condition, especially modified engines, unusual fuels, racing use, or equipment with special service restrictions.
Typical technical properties
Property
Value
Kinematic Viscosity at 100 C, cSt (ASTM D445)
15.6
Kinematic Viscosity at 40 C, cSt (ASTM D445)
116.4
Viscosity Index (ASTM D2270)
142
CCS Viscosity, cP at -20 C (ASTM D5293)
4,934
Pour Point, C (ASTM D97)
-40
Four-Ball Wear Test scar, mm (ASTM D4172)
0.45
NOACK Volatility, percent weight loss (ASTM D5800)
Signature Series 15W-40 Max-Duty Diesel Oil is available in quart bottle (DMEQT-EA), case of 12 quarts, gallon, 2.5 gallon, 55 gallon drum, and 275 gallon tote sizes. Using AMSOIL synthetic lubricants and practicing extended drain intervals does not void a new vehicle or equipment manufacturer warranty, and all AMSOIL lubricants and filters are covered by the AMSOIL Limited Warranty. Match the right diesel grade and OEM approval set with the AMSOIL Diesel Oil Guide, match the right product in the AMSOIL Vehicle Lookup Guide, then order AMSOIL Signature Series 15W-40 100% Synthetic Max-Duty Diesel Oil.
sticking to what works and what has been used in the truck before me
By David from iowa on July 20, 2026.
Would recommend this to a friend.
6.7 Powerstroke
I have been using this exclusively in my 2016 F350. It out performs the Motorcraft Oil by a large margin. I drive lots of short trips. The Florida temps in Spring, Summer and Fall are routinely above 90°F. The severe service schedule suits me for my driving style.
By Robert from St Augustine, Florida on July 16, 2026.
Would recommend this to a friend.
Click no more
I have always had a feint clicking from my Diesel. Put Amsoil in for the first time and no more clicking (knocking)
15W-40 is the workhorse heavy-duty diesel grade, but the Signature Series Max-Duty 15W-40 application table also lists API SN for gasoline service alongside the heavy-duty diesel categories, so the same oil can serve gasoline applications that specifically call for a 15W-40 SN-class oil. Always match the engine manufacturer specification before use.
How do I confirm current approvals?
Confirm the current API category, OEM approvals, and viscosity guidance on the live AMSOIL product page before service. Approval lists can change when formulas or manufacturer requirements are updated.
How long can the oil stay in service?
Use the current AMSOIL product guidance, your owner's manual, and oil-analysis results to set the service interval. Extended service depends on the engine, operating conditions, fuel, filtration, and maintenance history.
Can Signature Series Max-Duty be mixed with conventional or other synthetic diesel oils?
The formula is compatible with other conventional and synthetic engine oils, but mixing shortens oil life and reduces performance benefits. Extended drain intervals are not supported when oils have been mixed, and aftermarket oil additives are not recommended for use with AMSOIL synthetic diesel oils.
Will running Signature Series Max-Duty void a new diesel engine warranty?
No. Using AMSOIL synthetic lubricants and practicing extended drain intervals does not void a new vehicle or equipment manufacturer warranty, and all AMSOIL lubricants and filters are covered by the AMSOIL Limited Warranty.
Should this engine run a 15W-40, a 5W-40, or a 5W-30 instead?
The right grade depends on the engine manufacturer specification and the operating temperature range. Signature Series Max-Duty is offered in 5W-30 (DHD), 10W-30 (DTT), 0W-40 (DZF), 5W-40 (DEO), and 15W-40 (DME). Use the AMSOIL Diesel Oil Guide and the AMSOIL Vehicle Lookup Guide to confirm the correct grade for the engine.
Is Signature Series Max-Duty fully synthetic?
Yes. The line is built on top-tier synthetic base oils with a boosted heavy-duty additive package designed for thermal stability, soot dispersancy, and extended drain capability.
