AMSOIL vs. Castrol EDGE: Full-Synthetic Motor Oil Showdown

The short answer

If you want published spec transparency — HTHS viscosity, NOACK volatility, Total Base Number, and cold-cranking viscosity all printed on one public data bulletin — and third-party engine-test results to back up the numbers, AMSOIL Signature Series is the straightforward answer. Both brands are GM dexos® 1 Gen 3 approved in the 5W-30 and 0W-20 grades that owners most commonly buy. Both brands now offer a 25,000-mile drain-interval program in 5W-30: AMSOIL across the whole Signature Series line, Castrol via its EDGE Extended Performance 5W-30 (the EDGE Extended Performance 0W-20 tier is still labelled for up to 20,000 miles). The difference is in what each company prints on the data sheet: AMSOIL publishes HTHS, NOACK, and TBN; Castrol omits all three across every current EDGE variant.

National Synthetics is an Independent AMSOIL Dealer, and we stock Signature Series 5W-30 and 0W-20 locally for our Georgia customers.

Why this comparison matters now

• Dexos1 Gen 3 is the current GM passenger-car spec. Any 5W-30 or 0W-20 you buy for a modern Silverado, Tahoe, Suburban, Camaro, Malibu, Equinox, Traverse, or Cadillac passenger vehicle should meet it. AMSOIL Signature Series, the April 2025 Castrol EDGE 5W-30 U.S. PDS, the October 2024 Castrol EDGE 0W-20 PDS, and the February 2025 Castrol EDGE Extended Performance 5W-30 PDS all carry the Gen 3 approval.
• 25,000-mile drain intervals are no longer an AMSOIL-only claim in 5W-30. Castrol EDGE Extended Performance 5W-30 (February 2025 PDS) now claims up to 25,000 miles or 1 year. That makes spec transparency and engine-test evidence the real differentiators, not marketing mileage.
• Direct-injection and turbocharged engines need the NOACK and HTHS numbers. Low-speed pre-ignition, timing-chain wear, turbo coking, and intake-valve deposits all track with how the oil behaves under heat and shear. If the PDS does not print the values, you cannot verify how much margin the formulation has over the spec minimum.

Published physical and chemical properties — 5W-30

Every AMSOIL figure below is taken from the current AMSOIL Signature Series Synthetic Motor Oil data bulletin (G2880, February 2024). Castrol figures are taken from the current Castrol EDGE 5W-30 U.S. PDS (21 April 2025) and the current Castrol EDGE Extended Performance 5W-30 PDS (12 February 2025). Cells marked “Not published” reflect what the current Castrol PDSs do and do not list. Physical properties are typical values, not minimum/maximum specifications.

Property	AMSOIL Signature Series 5W-30 (ASL)	Castrol EDGE 5W-30 (U.S.)	Castrol EDGE Extended Performance 5W-30
Kinematic Viscosity @ 100 °C (cSt)	10.3	10.7	9.9
Kinematic Viscosity @ 40 °C (cSt)	59.7	63	60
Viscosity Index	162	158	163
HTHS Viscosity @ 150 °C (cP)	3.11	Not published	Not published
CCS Cold-Cranking Viscosity @ −30 °C (cP)	3,968	4,790	4,480
Pour Point (°C / °F)	−50 / −58	−42 / −44	−42 / −44
Flash Point, method (°C)	220 (ASTM D92, COC)	225 (ASTM D93, PMCC)	231 (ASTM D93, PMCC)
NOACK Volatility (% wt loss)	6.7	Not published	Not published
Total Base Number (mg KOH/g)	12.5	Not published	Not published
Sulfated Ash (% wt)	Listed in bulletin	Not published	0.77
API SP	Yes (also SN PLUS, SN)	— (API SQ)	— (API SQ)
GM dexos® 1 Gen 3	Yes	Yes	Yes

Sources: AMSOIL Signature Series Synthetic Motor Oil data bulletin (G2880, February 2024); Castrol EDGE 5W-30 U.S. Product Data Sheet (21 April 2025); Castrol EDGE Extended Performance 5W-30 Product Data Sheet (12 February 2025). Castrol, EDGE, and Fluid TITANIUM are trademarks of Castrol Limited. Dexos is a registered trademark of General Motors.

What the numbers actually mean

Film strength (HTHS) — the number Castrol does not print

HTHS — High-Temperature High-Shear viscosity at 150 °C — is the load-bearing film-thickness number. It is what protects rod bearings, cam lobes, and turbo journals once the oil is hot, sheared, and under load. The API SP and GM dexos® 1 Gen 3 specifications both set a 2.9 cP minimum for SAE xW-30.

AMSOIL Signature Series 5W-30 publishes 3.11 cP on the public data bulletin, confirmed against ASTM D5481. Castrol’s current EDGE 5W-30 and EDGE Extended Performance 5W-30 PDSs do not print an HTHS value. Both oils clear the specification minimum by virtue of their approvals — only AMSOIL lets you see how much margin there is.

Cold-flow protection where wear actually happens

Most engine wear happens in the first seconds after cold start, before oil pressure is fully established. Two published values matter here: CCS (Cold-Cranking Simulator, ASTM D5293) and pour point (ASTM D97).

• CCS @ −30 °C: AMSOIL Signature Series 5W-30 publishes 3,968 cP. Castrol EDGE 5W-30 publishes 4,790 cP. Castrol EDGE Extended Performance 5W-30 publishes 4,480 cP. Lower is better — the AMSOIL oil reaches the bearings faster when the engine is cold-cranked.
• Pour point: AMSOIL Signature Series 5W-30 publishes −50 °C / −58 °F. Both current Castrol 5W-30 PDSs publish −42 °C / −44 °F. That is an 8 °C (14.4 °F) advantage for AMSOIL, using the same ASTM D97 method.

NOACK volatility — less burn-off, fewer deposits

NOACK (ASTM D5800) measures how much oil evaporates off under sustained heat. Lower NOACK means less oil consumption between top-ups, cleaner intake valves on direct-injection engines, and less risk of LSPI in turbocharged engines.

AMSOIL Signature Series 5W-30 publishes 6.7 %. Castrol does not publish a NOACK value for EDGE 5W-30 or EDGE Extended Performance 5W-30 on the current PDS.

TBN drives drain interval

Total Base Number (ASTM D2896) is the additive package’s reserve to neutralize acids before they attack bearings and rings. A higher TBN does not mean better protection day one — it means the oil keeps protecting longer, which is the basis for an extended-drain guarantee.

AMSOIL Signature Series publishes a TBN of 12.5 across the entire line, from 0W-16 through 5W-50. Castrol does not publish a TBN value for EDGE 5W-30 or EDGE Extended Performance 5W-30 on the current PDS.

Spec transparency is itself a buying signal

Across the table above, AMSOIL publishes the full data bulletin — viscosity index, HTHS, CCS, pour/flash/fire, NOACK, TBN — in one place. Castrol’s current EDGE and EDGE Extended Performance 5W-30 PDSs omit HTHS, NOACK, and TBN. Both companies have those values internally; only AMSOIL publishes them.

AMSOIL engine-test results vs. industry minimums

AMSOIL publishes the following Signature Series test results, run against the current industry-standard procedures. Every figure is from the AMSOIL Signature Series data bulletin (G2880, February 2024). Castrol does not publish equivalent per-test figures on the current EDGE or EDGE Extended Performance Product Data Sheets.

Published physical and chemical properties — 0W-20

The 0W-20 grade is where most 2011-and-newer passenger cars actually land: Toyota, Honda, Nissan, Ford, and GM SUVs and a growing share of trucks. AMSOIL figures are from the AMSOIL Signature Series data bulletin (G2880, February 2024). Castrol figures are from the current Castrol EDGE 0W-20 U.S. PDS (1 October 2024) and Castrol EDGE Extended Performance 0W-20 PDS (11 November 2022).

Property	AMSOIL Signature Series 0W-20 (ASM)	Castrol EDGE 0W-20 (U.S.)	Castrol EDGE Extended Performance 0W-20
Kinematic Viscosity @ 100 °C (cSt)	8.8	8.6	8.2
Kinematic Viscosity @ 40 °C (cSt)	47.1	47	44
Viscosity Index	169	162	166
HTHS Viscosity @ 150 °C (cP)	2.67	Not published	Not published
CCS Cold-Cranking Viscosity @ −35 °C (cP)	5,122	5,900	5,800
Pour Point (°C / °F)	−53 / −63	−42 / −44	−42 / −44
NOACK Volatility (% wt loss)	8.5	Not published	Not published
Total Base Number (mg KOH/g)	12.5	Not published	Not published
GM dexos® 1 Gen 3	Yes	Yes	Yes
Drain-interval program	Up to 25,000 mi / 1 yr (normal service)	Standard OEM interval	Up to 20,000 mi / 1 yr

Notes: CCS is reported at −35 °C for 0W-grade oils per SAE J300. The Castrol EDGE Extended Performance 0W-20 PDS (November 2022) prints a 20,000-mile drain-interval claim; the 5W-30 tier of EDGE Extended Performance was updated to a 25,000-mile claim on the February 2025 PDS. AMSOIL’s 25,000-mile coverage in normal service applies across the full Signature Series line, including 0W-20 (ASM).

Approvals and fitment matrix (5W-30)

Specification	AMSOIL Signature Series 5W-30 (ASL)	Castrol EDGE 5W-30 (U.S.)	Castrol EDGE Extended Performance 5W-30
API SP	Yes	— (API SQ)	— (API SQ)
API SN PLUS	Yes	—	—
GM dexos® 1 Gen 3	Yes	Yes	Yes
ACEA A5/B5	Yes	Yes	Yes
ACEA A1/B1	Yes	—	—
ACEA C2	—	Yes	Yes
Ford WSS-M2C946-B1	Yes	Yes	Yes
Chrysler MS-6395	Yes	Yes	Yes
Honda HTO-06	Yes	Yes	Yes

A dash (—) means the manufacturer does not publicly list that approval for that oil on the current PDS. Note that API SQ is the most recent passenger-car specification and supersedes API SP — a bottle carrying API SQ satisfies engines that originally specified API SP or earlier. Always confirm against the current data bulletin and your owner’s manual before service.

Use-case guidance

Modern daily drivers — Honda, Toyota, Nissan, Ford, and GM passenger cars

Most call for 0W-20 meeting the appropriate OEM sub-spec. AMSOIL Signature Series 0W-20 (ASM) carries GM dexos® 1 Gen 3, Ford WSS-M2C947-B1, and Chrysler MS-6395 on the Signature Series data bulletin. Its published 2.67 cP HTHS and 8.5 % NOACK are on the PDS — not implied by the approval.

2011-and-newer GM trucks, SUVs, and passenger cars — dexos1 Gen 3

5.3L, pre-recall 6.2L, 3.6L Pentastar (Jeep/Chrysler applications), Ecotec, and turbocharged GM platforms all specify a dexos® 1 Gen 3 oil in the 5W-30 or 0W-20 grade. AMSOIL Signature Series 5W-30 (ASL), Castrol EDGE 5W-30 U.S. (April 2025 PDS), and Castrol EDGE Extended Performance 5W-30 (February 2025 PDS) all carry Gen 3. Bottles still on shelves from earlier Castrol formulations may list dexos1 Gen 2 — check the label before buying.

Turbocharged and direct-injection engines

Boost adds heat; gasoline direct-injection adds intake-valve deposit risk. Both issues track with NOACK volatility. AMSOIL Signature Series 5W-30 publishes 6.7 % on the data bulletin. Castrol does not publish a NOACK value for EDGE or EDGE Extended Performance 5W-30. Signature Series also delivered a 3.6 % turbo-coking temperature rise (vs. the 13 % pass limit) in the GM dexos1 Turbo Coking test, per the AMSOIL data bulletin.

Fleet service, towing, and high-idle operation

These are the conditions AMSOIL’s severe-service drain interval was designed for: up to 15,000 miles, 700 hours, or one year, whichever comes first. Castrol EDGE Extended Performance carries a 25,000-mile claim in the 5W-30 tier but does not publish a separate severe-service sub-interval. For commercial fleets, excessive idling, or dusty-duty applications, AMSOIL’s written severe-service coverage is the clearer answer. See our AMSOIL oil change interval guide for the full breakdown.

Cold-climate operation

AMSOIL Signature Series 5W-30 publishes a −50 °C / −58 °F pour point and 3,968 cP CCS at −30 °C. Castrol EDGE Extended Performance 5W-30 publishes −42 °C pour point and 4,480 cP CCS at −30 °C. If your vehicle sees cold-soaked starts below 0 °F, the AMSOIL data sheet shows a measurable advantage in both pumping and cold-cranking.

Extended drain intervals — both brands, different coverage

AMSOIL guarantees Signature Series for up to 25,000 miles, 700 hours, or one year in normal personal-vehicle service, and up to 15,000 miles, 700 hours, or one year in severe service (commercial or fleet vehicles, excessive idling, frequent towing, hauling, plowing, or driving in dusty conditions), per the G2880 data bulletin. The coverage is written, not implied, and applies across the full Signature Series line — 0W-16 through 5W-50.

Castrol EDGE Extended Performance 5W-30 (February 2025 PDS) now carries a 25,000-mile or 1-year claim. The 0W-20 tier of EDGE Extended Performance (November 2022 PDS) carries a 20,000-mile or 1-year claim. Standard Castrol EDGE (not Extended Performance) is sold for normal OEM-interval service, not an extended-drain program.

For owners who actually run long miles — fleet pickups, daily commuters, rideshare drivers — the math favors AMSOIL once the published severe-service interval and Preferred Customer wholesale pricing are factored in.

Frequently Asked Questions

Is AMSOIL Signature Series better than Castrol EDGE?

On the data sheet, AMSOIL Signature Series prints its HTHS viscosity, NOACK volatility, cold-cranking viscosity, and Total Base Number. Castrol does not publish HTHS, NOACK, or TBN on the current EDGE or EDGE Extended Performance Product Data Sheets. AMSOIL also publishes third-party engine-test results in the Sequence IVA cam-wear, Sequence IIIH piston-cleanliness, Sequence VG sludge, GM dexos1 LSPI, and GM Turbo Coking tests. Both brands are GM dexos1 Gen 3 approved and both now offer a 25,000-mile drain-interval program in 5W-30 (AMSOIL across the whole Signature Series line, Castrol via EDGE Extended Performance 5W-30).

How does AMSOIL Signature Series 5W-30 compare to Castrol EDGE on HTHS and NOACK?

AMSOIL Signature Series 5W-30 (ASL) publishes an HTHS viscosity of 3.11 cP at 150°C (ASTM D5481) and a NOACK volatility of 6.7 percent (ASTM D5800) in the Signature Series data bulletin (G2880, February 2024). Neither value is printed on the current Castrol EDGE 5W-30 U.S. PDS (April 2025) or Castrol EDGE Extended Performance 5W-30 PDS (February 2025). Both oils clear the API and dexos1 Gen 3 HTHS minimums by virtue of their approvals, but only AMSOIL shows the number.

Can I switch from Castrol EDGE to AMSOIL without flushing?

Yes. AMSOIL Signature Series is fully compatible with other conventional and synthetic motor oils, so no flush is required. Drain the old oil at temperature, replace the filter, and fill with AMSOIL. Mixing oils long-term will shorten the drain interval and reduce the performance benefit, so plan the changeover as a clean swap.

Does using AMSOIL instead of Castrol EDGE void my new-vehicle warranty?

No. The Magnuson-Moss Warranty Act prohibits manufacturers from voiding a warranty solely because you use a qualifying aftermarket lubricant. As long as the oil meets the required specification on the cap — for example, GM dexos1 Gen 3, Ford WSS-M2C946-B1, or Chrysler MS-6395 — your warranty remains intact. Keep your purchase receipts and oil-change records.

How long can I safely go between oil changes on AMSOIL Signature Series?

AMSOIL guarantees Signature Series for up to 25,000 miles, 700 hours, or one year in normal personal-vehicle service, and up to 15,000 miles, 700 hours, or one year in severe service (commercial use, excessive idling, frequent towing, hauling, plowing, or driving in dusty conditions). Always honour the OEM service interval if it is shorter — particularly during a manufacturer warranty period. See our oil change interval guide.

Is Castrol EDGE Extended Performance equivalent to AMSOIL Signature Series?

Castrol EDGE Extended Performance 5W-30 (February 2025 PDS) now carries its own "up to 25,000 miles or 1 year" claim, matching AMSOIL on paper in that grade. The 0W-20 tier of EDGE Extended Performance (November 2022 PDS) is still labelled for up to 20,000 miles. The differences show up in what each PDS prints: AMSOIL Signature Series publishes HTHS, NOACK, TBN, CCS, and engine-test results; Castrol EDGE Extended Performance publishes CCS but omits HTHS, NOACK, and TBN.

Is AMSOIL Signature Series approved for GM dexos1 Gen 3 like Castrol EDGE?

Yes. AMSOIL Signature Series 0W-20 (ASM), 5W-20 (ALM), 0W-30 (AZO), and 5W-30 (ASL) all carry the current GM dexos1 Gen 3 approval per the AMSOIL Signature Series data bulletin (G2880, February 2024). The current Castrol EDGE 5W-30 U.S. PDS (April 2025), Castrol EDGE 0W-20 U.S. PDS (October 2024), and Castrol EDGE Extended Performance 5W-30 PDS (February 2025) also list dexos1 Gen 3. Earlier Castrol PDSs may still show dexos1 Gen 2 — always check the bottle label.

Why does AMSOIL publish more specs than Castrol on the data sheet?

AMSOIL prints the full typical-properties table — kinematic viscosity at 40°C and 100°C, viscosity index, HTHS, CCS, pour point, flash and fire points, NOACK volatility, and TBN — on the public Signature Series data bulletin. Castrol's current EDGE and EDGE Extended Performance Product Data Sheets omit HTHS, NOACK, and TBN. Both companies have those internal numbers; only AMSOIL publishes them.

Does AMSOIL offer wear-test data the way Castrol does?

AMSOIL publishes third-party engine-test results for Signature Series in the Sequence IVA cam-wear test (20.28 µm average cam wear vs. the 90 µm API SN PLUS limit, per ASTM D6891), the GM dexos1 LSPI test (zero LSPI events across five consecutive tests), the GM Turbo Coking test (3.6 percent temperature rise vs. 13 percent pass limit), the Sequence VG / ASTM D6593 sludge test (90 percent better than the API SN PLUS standard), and the Sequence IIIH / ASTM D8111 piston-cleanliness test (40 percent cleaner pistons than required, even at double the standard test length). Castrol's current public Product Data Sheets do not list individual engine-test values.

Where can I buy AMSOIL Signature Series through National Synthetics?

Order direct from AMSOIL.com using our dealer link for ship-direct or local pickup. Becoming an AMSOIL Preferred Customer unlocks wholesale pricing on every reorder.

Recommended AMSOIL Products

Talk to your local AMSOIL dealer

National Synthetics has been supplying AMSOIL products to Georgia drivers, fleets, and shops for over a decade. If you are switching from Castrol EDGE and want to confirm the right AMSOIL grade for your vehicle — dexos® 1 Gen 3, Ford WSS-M2C946-B1 or WSS-M2C947-B1, Chrysler MS-6395, or Honda HTO-06 — call us.

Phone: 1-678-944-8816
Dealer #: 1858536
Order direct: AMSOIL Signature Series 5W-30 (ASL)

Related reading

• Why buy AMSOIL Signature Series
• Understanding oil viscosity
• Understanding engine oil specifications
• AMSOIL oil change interval guide
• The history of synthetic oil and AMSOIL
• About AMSOIL

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Castrol, EDGE, Extended Performance, and Fluid TITANIUM are trademarks of Castrol Limited. Dexos is a registered trademark of General Motors. Ford, Chrysler, Honda, Jaguar Land Rover, Toyota, and Nissan marks are the property of their respective owners. National Synthetics is an Independent AMSOIL Dealer and is not affiliated with Castrol Limited, General Motors, or any vehicle manufacturer named in this article. All product specifications are taken from each manufacturer’s current published Product Data Bulletin or Product Data Sheet and are subject to change without notice — always confirm against the current data bulletin and your owner’s manual before service.