Many premium motor oils claim to be the best. The bottles look alike, the marketing sounds alike and they carry the same industry certifications. So how do you tell them apart?
The easiest way is to look past the label and identify what the oil has been tested against, and how far it measures above the industry-standard baselines. Here’s how to compare the synthetic motor oils of competing brands, using AMSOIL Signature Series® 100% Synthetic Motor Oil as the example of what to look for.
Start with the specification, but don’t stop there
Your owner’s manual lists the viscosity and performance specifications your engine requires, such as API SQ and ILSAC GF-7, or an automaker specification. Any oil you consider should meet the recommendations for your specific vehicle.
But those industry specifications are the minimum. Passing tells you an oil cleared the lowest bar. It doesn’t tell you how far over the bar it went. That’s where the real differences between premium synthetic oils show up.
Shear resistance identifies stronger protective oil film
Viscosity is an oil’s most important property. Your engine relies on an oil film thinner than a sheet of paper to keep metal parts from contacting and causing wear. Shearing is caused when the high temperatures and pressures inside your engine physically tear an oil apart at the molecular level, thinning the viscosity. High-horsepower, high-rpm engines increase that risk.
Look for oils built on naturally shear-resistant synthetic base oils combined with shear-stable additives that help retain viscosity under high heat and pressure.
Volatility: how much of your oil boils away
Volatility is an oil’s tendency to evaporate at high temperatures. Oil that evaporates has to be topped off, and what’s left behind can thicken and form deposits. The ASTM D5800 NOACK test measures how much oil weight is lost to evaporation; the lower the number, the better.
AMSOIL Signature Series 0W-20 had a result of 7.2% in the NOACK test, compared with the 15.0% maximum allowed by the API SQ specification – 2X better protection against volatility.1
Deposit control: the Sequence IIIH test
Piston deposits rob performance and efficiency. The Sequence IIIH test runs an engine under high heat and load for 90 hours, then rates how clean the pistons remain.
Signature Series provides 72% more protection against piston-deposit formation than industry standards.2 Even when the test length was doubled, it delivered 31% better protection than required.3 An oil that stays clean in a double-length test is an oil that holds up over a long drain interval.
LSPI protection after miles of use
Low-speed pre-ignition (LSPI) can destroy a turbocharged, direct-injection engine in a single event. The Sequence IX test measures how well an oil prevents it, and the aged-oil version tests oil that has already been in service.
That second part matters. Even after 25,000 miles of use, Signature Series delivers 4X more piston protection against LSPI.4 Ask whether an oil protects at the end of its drain interval, not just fresh out of the bottle.
Real-world results over real miles
Lab tests are only part of the story. AMSOIL ran Signature Series 5W-30 in a 2025 Ford* F-150 Raptor* through a 125,000-mile accumulation study, changing the oil at 25,000-mile intervals.
- Horsepower and torque were preserved from the start of the test to the end.5
- The oil screen had 0% plugging – no sludge.6
Does the brand stand behind it?
Finally, look at the drain interval the manufacturer is willing to guarantee. Signature Series provides guaranteed protection for up to 25,000 miles or one year in normal service, whichever comes first. Most other oils will recommend the minimum vehicle manufacturer guideline for oil drain intervals.
Questions to ask about any motor oil
- Which industry tests were run, and are they named?
- How far did the oil exceed the specification limit, not just whether it passed?
- Was it tested after extended use, or only when new?
- Do the claims the list specific oil grade, test performed and conditions?
- Does the manufacturer guarantee the drain interval?
See the full test results in AMSOIL Signature Series Motor Oil: What the Tests Show and find the right AMSOIL products for your vehicle in the AMSOIL Product Guides.
Frequently asked questions
Is AMSOIL better than other synthetic motor oils?
Compare test results, not labels. AMSOIL Signature Series 100% Synthetic Motor Oil is tested well beyond industry minimums. It delivers 2X better protection against volatility,1 72% more protection against piston deposits than industry standards2 and 4X more piston protection against LSPI, even after 25,000 miles of use.4 See every result in AMSOIL Signature Series Motor Oil: What the Tests Show.
Is AMSOIL worth it?
Yes – the value is in the drain interval. Signature Series provides guaranteed protection for up to 25,000 miles or one year in normal service, so one oil change can do the work of several shorter ones. That means fewer oil changes, less oil to buy, less time in the garage and less waste oil to recycle. See the value per mile in A Data-Driven Guide to Slashing Maintenance Costs with AMSOIL.
How long does AMSOIL synthetic motor oil last?
In normal service, Signature Series lasts up to 25,000 miles, 700 hours of operation or one year, whichever comes first. In severe service, such as frequent towing, hauling, plowing, excessive idling or dusty conditions, it lasts up to 15,000 miles, 700 hours or one year. Use an AMSOIL Oil Filter for the full interval; with other brands of filters, don’t exceed 12,000 miles or one year unless your vehicle manufacturer recommends longer. Details are in AMSOIL Oil Change Interval.
Can I switch to AMSOIL from another synthetic oil?
Yes. Signature Series is compatible with other conventional and synthetic motor oils, so you can switch at your next oil change. Drain the old oil completely: mixing other oils with AMSOIL shortens the oil’s life and reduces its performance benefits, and AMSOIL doesn’t support extended drain intervals with mixed oils. Learn more in Can You Mix AMSOIL With Other Motor Oil?.
Will AMSOIL void my new-vehicle warranty?
No. Using AMSOIL synthetic lubricants does not void your new-vehicle or equipment manufacturer’s warranty, and all AMSOIL lubricants and filters are covered by the AMSOIL Limited Warranty. Choose the viscosity and specifications your owner’s manual requires, and find the right products in Which AMSOIL Motor Oil Is Right for You?.
Where can I find AMSOIL reviews from real drivers?
Read AMSOIL Customer Stories: Real-World Results for results from everyday drivers, racers and fleet owners, and see customer product reviews on AMSOIL.com.
1Based on AMSOIL Signature Series 0W-20 100% Synthetic Motor Oil compared to the API SQ limit using the ASTM D5800 NOACK volatility test. 2Based on AMSOIL Signature Series 5W-30 100% Synthetic Motor Oil results in the Sequence IIIH test. 3Based on AMSOIL Signature Series 5W-30 100% Synthetic Motor Oil results in a double-length Sequence IIIH test. 4Based on AMSOIL Signature Series 5W-30 100% Synthetic Motor Oil in the Sequence IX aged-oil LSPI test after 25,000-mile service interval. 5Based on comparative start- and end-of-test horsepower and torque measurements in a 125,000-mile accumulation study with AMSOIL Signature Series 5W-30 100% Synthetic Motor Oil in a 2025 Ford* F-150 Raptor* equipped with a 3.5L high-output engine. 6As demonstrated in a 125,000-mile accumulation study using AMSOIL Signature Series 5W-30 100% Synthetic Motor Oil in a 2025 Ford* F-150 Raptor* equipped with a 3.5L high-output engine which had 0% oil-screen plugging.
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David Hilgendorf is an AMSOIL Technical Writer who develops content for automotive, powersports and industrial audiences. His work includes technical data sheets, magazine articles, blog posts, white papers, product literature and application guidance. Hilgendorf works with engineers, laboratory personnel and technical specialists to communicate lubricant testing, product performance, maintenance practices, metalworking fluids, grease, motorcycles, marine equipment and industrial reliability.
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