AMSOIL Premium Protection 10W-40 100% Synthetic Motor Oil
AMSOIL Premium Protection 10W-40 Synthetic Motor Oil is built for high-mileage and hard-working engines that run hot, haul heavy, or head off road. It adds the extra anti-wear protection that engines with flat-tappet cams and high-tension valve springs need.
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Product data sheets
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AMSOIL Premium Protection 10W-40 100% Synthetic Motor Oil
AMSOIL Premium Protection 10W-40 100% Synthetic Motor Oil is a high-viscosity, high-zinc gasoline and diesel engine oil engineered for older, modified, and high-stress engines that call for an SAE 10W-40 grade. The formulation pairs a heavy zinc and anti-wear additive treatment with full synthetic base oils, a strong fit for high-mileage vehicles, flat-tappet cams with high-tension valve springs, towing and hauling duty, off-road service, and wet-clutch motorcycles.
Heavy zinc treatment for flat-tappet cams and high-stress engines
Premium Protection 10W-40 is built around a heavy treatment of zinc and other anti-wear additives that protect the load-bearing surfaces inside engines and transmissions. The high-zinc package shields cam lobes, lifters, gears, and bearings during the boundary-lubrication moments that occur at startup and under heavy throttle. That positions the formula in the right service window for flat-tappet cams with high-tension valve springs, performance and modified street engines, and older designs originally specified on motor oils carrying API SL, SJ, SH, or SG service categories.
Wet-clutch compatibility for motorcycles and shared-sump applications
The 10W-40 formula contains no friction modifiers, so it meets JASO MA for motorcycle wet-clutch service. Friction modifiers can glaze the clutch plates in shared-sump motorcycles and many ATV powertrains and lead to slip under load. Premium Protection 10W-40 preserves clean clutch engagement and steady transmission operation in metric four-stroke street and adventure bikes, dirt bikes, and power equipment where the engine oil also lubricates the clutch and gearbox. For grade selection on a specific bike, refer to the Motorcycle Oil Guide.
Shear stability and viscosity retention under load
Operating viscosity is what holds the oil film between moving parts during long pulls. Premium Protection 10W-40 resists viscosity loss due to shear and arrives at 14.6 cSt at 100 C in ASTM D445 testing. The high-temperature, high-shear viscosity holds at 4.3 cP in ASTM D5481, above the 3.7 cP minimum required of an SAE 40-grade oil under SAE J300. A viscosity index of 158 in ASTM D2270 means the formulation thins less between cold and hot than a typical mineral 10W-40, which helps maintain pressure during heavy hauling and off-road service.
Thermal stability, oxidation control, and clean operation
High heat is the fastest way to break a motor oil down, especially in air-cooled engines, modified street builds, and trucks pulling heavy loads. The full synthetic chemistry in Premium Protection 10W-40 controls volatilization, oxidation, and deposit formation across the operating range. NOACK volatility comes in at 6.5 percent weight loss in ASTM D5800, which limits the amount of oil that boils away into the PCV system at high temperature. A flash point of 226 C in ASTM D92 and a pour point of -42 C in ASTM D97 give the formula a wide working range for hot summer towing and cold winter starts alike.
TBN reserve, soot dispersion, and gasoline-or-diesel flexibility
A combined gasoline and diesel additive package allows Premium Protection 10W-40 to neutralize acids and disperse soot across long drain intervals in mixed fleets. Total Base Number is 12.1, providing reserve detergent and acid-neutralization capacity for diesel service categories API CI-4+, CI-4, CH-4, CF, and CF-2, plus older gasoline categories API SL, SJ, SH, and SG. The Four-Ball Wear Test (ASTM D4172) returned a 0.48 mm wear scar, illustrating the load-carrying margin built into the high-zinc additive system.
Recommended applications and service intervals
Premium Protection 10W-40 is recommended for air-cooled and liquid-cooled gasoline and diesel engines, transmissions, and chaincase applications that require an SAE 10W-40 viscosity and any of the following specifications: API SL, SJ, SH, SG; API CI-4+, CI-4, CH-4, CF, CF-2; ACEA A3/B3, E3, E5; ISO-L-EMA; JASO MA; Caterpillar ECF-1; Cummins 20071/20072/20076/20077; MAN 271/3275; MB 228.1, 228.3, 229.1; MTU Type 2; Volvo VDS-2, VDS; Mack EO-M+, EO-M; and Detroit Diesel 93K214. The grade is built for older, modified, and high-stress engines, not for late-model gasoline cars that require API SP, SN Plus, SN, or ILSAC GF-6.
Diesel normal service: up to 25,000 miles or one year, whichever comes first, in unmodified, mechanically sound vehicles, or longer based on oil analysis.
Diesel severe service: up to 15,000 miles or one year, whichever comes first, or longer based on oil analysis.
Gasoline normal and severe service: up to 15,000 miles or one year, whichever comes first, or longer based on oil analysis.
Motorcycles, small engines, stationary engines, heavy equipment, and other applications: extend drain intervals based on oil analysis or follow the manufacturer-recommended drain interval.
AMSOIL Ea Full-Flow Oil Filters are designed for extended drain intervals and should be replaced when the oil is changed; other-brand filters should be changed at standard OEM intervals. Premium Protection 10W-40 is compatible with synthetic and conventional motor oils, but mixing shortens oil life and reduces performance benefits, and extended drain intervals are not supported when oils have been mixed. Aftermarket oil additives are not recommended for use with AMSOIL synthetic motor oils.
Typical technical properties
Property
Value
Kinematic Viscosity at 100 C, cSt (ASTM D445)
14.6
Kinematic Viscosity at 40 C, cSt (ASTM D445)
95.9
Viscosity Index (ASTM D2270)
158
CCS Viscosity, cP at -25 C (ASTM D5293)
4920
Pour Point, C (ASTM D97)
-42
Flash Point, C (ASTM D92)
226
Fire Point, C (ASTM D92)
240
High-Temperature High-Shear Viscosity at 150 C, cP (ASTM D5481)
4.3
Four-Ball Wear Test, Scar, mm (ASTM D4172)
0.48
NOACK Volatility, percent weight loss (ASTM D5800)
6.5
Total Base Number
12.1
Order Premium Protection 10W-40
Premium Protection 10W-40 is available in a quart bottle (AMOQT-EA), case of 12 quarts (AMOQT-CA), gallon jug (AMO1G-EA), case of four gallons (AMO1G-CA), 2.5-gallon jug (AMOTP-EA), case of two 2.5-gallon jugs (AMOTP-CA), and 55-gallon drum (AMO55-EA). All AMSOIL lubricants and filters are covered by the AMSOIL Limited Warranty, and using AMSOIL synthetic lubricants does not void a new vehicle or equipment manufacturer warranty. Match the right product with the AMSOIL Vehicle Lookup Guide, compare viscosity options for passenger applications in the Car Oil Guide, then order AMSOIL Premium Protection 10W-40 100% Synthetic Motor Oil.
My 2005 GMC Savanna has 290.000 km. Ever since using Amsoil Premium Protection 20-50 synthetic motor oil. My engine sounds new, less mechanical sounds related to high mileage, better performance and fuel economy. Excellent product. Thanks
By Stevie from East York, Ontario, Canada 🇨🇦 on May 27, 2026.
Would recommend this to a friend.
10w40 high zinc oil
I use this in my 2013 subaru wrx with built ej2.5l with outfront motorsports forged pistons built block . Been amazing oil for this built engine. Change every 3000 . Still looks good. 40,000 miles on build using same oil!
By Brandon from AZ on March 23, 2026.
Would recommend this to a friend.
Great oil
Great products as always
By david from Cartersville GA on February 24, 2026.
Why is Premium Protection 10W-40 considered a high-zinc motor oil?
The formulation carries a heavy treatment of zinc and other anti-wear additives. Zinc dialkyldithiophosphate (ZDDP) is the industry workhorse for boundary-layer wear protection on cam lobes, lifters, and other high-pressure surfaces. Premium Protection 10W-40 dials that treatment higher than current API SP and ILSAC GF-6 oils carry, which is why the grade fits flat-tappet cams, high-tension valve springs, and modified or older engines that benefit from more anti-wear chemistry than catalyst-friendly modern oils provide.
Is Premium Protection 10W-40 a true full synthetic?
Yes. Premium Protection 10W-40 is a 100 percent synthetic motor oil. The synthetic base oil and additive system together control oxidation, volatilization, and viscosity loss across long, hot drain intervals.
Which engines should use Premium Protection 10W-40 instead of an API SP oil?
Choose Premium Protection 10W-40 for engines that specify SAE 10W-40 viscosity and that benefit from a higher zinc anti-wear package: high-mileage cars and trucks, modified gasoline engines, flat-tappet performance builds, towing and hauling rigs, off-road equipment, motorcycles that require JASO MA, older diesel pickups, and air-cooled small engines. Late-model gasoline cars that require API SP, SN Plus, SN, or ILSAC GF-6 should use a current Signature Series, XL, or OE grade in the manufacturer-specified viscosity.
Can Premium Protection 10W-40 be used in a wet-clutch motorcycle?
Yes. The formulation contains no friction modifiers and meets JASO MA, the wet-clutch standard for many four-stroke metric motorcycles, dirt bikes, and shared-sump powertrains. Always cross-check the owner manual for the required viscosity and JASO category before topping off.
How long can Premium Protection 10W-40 stay in service?
In unmodified, mechanically sound diesel engines, Premium Protection 10W-40 supports drain intervals up to 25,000 miles or one year for normal service and up to 15,000 miles or one year for severe service, whichever comes first. In gasoline engines, the cap is up to 15,000 miles or one year for both normal and severe service. Motorcycles, small engines, stationary engines, and heavy equipment should follow oil analysis or the manufacturer-recommended drain interval. Pairing with AMSOIL Ea Full-Flow Oil Filters is recommended to take full advantage of the extended interval.
Does AMSOIL synthetic motor oil void a new vehicle warranty?
No. Using AMSOIL synthetic lubricants does not void a new vehicle or equipment manufacturer warranty, and all AMSOIL lubricants and filters are covered by the AMSOIL Limited Warranty.
