If your owner’s manual says synthetic, use synthetic; otherwise any oil that meets every listed requirement is acceptable, whether it’s synthetic, a blend or conventional. Manufacturers differ. GM requires full-synthetic dexos1 oil in the 2023 Silverado’s V8s (manual, p. 340), Subaru requires 0W-20 synthetic in the 2023 Outback (manual, pp. 562–563), and Ford recommends a 5W-30 synthetic blend for the 2022 F-150’s 3.5L EcoBoost (manual, p. 573).
If the manual requires synthetic oil or only suitable products are synthetic, use it. If both types are permitted and both carry the complete requirement, compare current product data, operating conditions, availability, and price.
Watch: Synthetic vs. Conventional Oil
Editorial correction: the video's teardown, “four times wear,” turbo repair price, volatility ranges, and blend-percentage claims are not supported as universal comparisons. Use the product-level and vehicle-specific method below.
What owner’s manuals actually require
| Vehicle | What the manual specifies | Base-oil type named? |
|---|---|---|
| 2023 Chevrolet Silverado 1500 (5.3L and 6.2L V8) | SAE 0W-20 full synthetic, dexos1 approved | Yes: full synthetic |
| 2023 Subaru Outback (2.5L) | 0W-20 synthetic; 5W-30 conventional only for topping up | Yes: synthetic |
| 2022 Ford F-150 (3.5L EcoBoost) | Motorcraft SAE 5W-30 Synthetic Blend, WSS-M2C961-A1 | Yes: synthetic blend |
Sources: Silverado manual, p. 340; Outback manual, pp. 562–563; F-150 manual, p. 573. Our vehicle lookup shows the requirement for other models, with the manual page cited.
The API certification system itself doesn’t separate the types: the API Motor Oil Guide defines its categories and the “Starburst” and “Shield” marks by tested performance, and doesn’t distinguish synthetic from conventional oil. A conventional oil and a synthetic can carry the same API mark.
Full synthetic vs synthetic blend
A synthetic blend mixes synthetic and conventional base oils. The API categories and certification marks don’t define a minimum proportion, and the front label won’t tell you how much synthetic is in it. In practice:
- If the manual says “full synthetic” (like GM’s dexos1 requirement above), a blend isn’t a substitute unless it carries the exact approval required.
- If the manual names a blend (like Ford’s Motorcraft 5W-30 Synthetic Blend), a full synthetic carrying the same Ford specification also meets it. The specification is what matters.
- If the manual lists only a grade and category (common in Toyota manuals, which call for ILSAC-certified oil of a given viscosity), any product with that certification and grade qualifies.
The direct comparison
| Question | What the label can tell you | What still needs evidence |
|---|---|---|
| Is it synthetic or conventional? | The marketer’s product type | Exact base-stock composition may not be disclosed |
| Is it the right viscosity? | The SAE grade on the label | Whether that grade is permitted for your vehicle |
| Does it meet a service category? | API mark or stated ACEA claim | Exact category, market, and current licensing or claim status |
| Does it meet an OEM requirement? | Named approval or recommendation wording | Whether the exact product/grade is formally approved and current |
| Will it last longer? | Nothing universal | Vehicle schedule, operating conditions, and product-level test data |
The best buying order is compatibility first, then comparative performance.
What “synthetic” does not prove
The word alone does not prove a specific evaporation loss, cold-cranking result, deposit performance, fuel-economy improvement, or service interval. Those depend on the exact formulation and test result.
ASTM D5800, for example, defines standard methods for measuring evaporation loss. It does not state that every conventional oil falls within one range or every synthetic within another. Use the exact product’s current technical data sheet when comparing volatility, and make sure the test method is the same.
The same caution applies to base-oil groups. A consumer label usually does not disclose enough information to reconstruct the complete formulation, and additive chemistry also affects finished-oil performance.
Heat, cold, and turbochargers
Heat and cold are legitimate reasons to pay attention to tested performance, but they do not create universal rules. Compare the permitted SAE grades in the vehicle manual, then look at relevant product data such as cold-cranking, pour point, viscosity index, or evaporation loss where published.
For a turbocharged engine, use the exact oil specification required by the manufacturer. Do not infer that every turbo requires one base-oil type, one viscosity, or one interval. If a temperature or oil-pressure warning appears, synthetic oil is not a repair; follow the vehicle’s shutdown and diagnostic procedure.
How to compare two compatible products
Once both products match the complete vehicle requirement:
- Confirm the exact product name and grade—not just the brand family.
- Compare current approvals or licensing.
- Use comparable test methods from current technical data sheets.
- Check bottle size, local price, and availability without assuming price equals protection.
- Keep the manufacturer service interval unless qualified vehicle-specific guidance says otherwise.
Shell’s own product pages illustrate the proper scope: the company describes performance attributes for its named semi-synthetic and full-synthetic formulations. Those statements support those products, not a universal number for every oil in the category.
Frequently Asked Questions
Does my car need full synthetic?
Use the owner’s manual. If it requires synthetic, follow it. If it specifies only performance requirements, choose a product that satisfies every listed requirement and any formal approval wording.
Can synthetic oil extend my change interval?
Not by itself. Follow the vehicle’s maintenance schedule or oil-life system. An extended-drain marketing claim does not override the manual.
Can I switch from conventional to synthetic at high mileage?
Do not use a universal mileage threshold. First check for active leaks, abnormal consumption, and the permitted specification; then follow manufacturer or qualified service guidance for that engine.
Is full synthetic better than synthetic blend?
Only if your manual requires full synthetic, or the full-synthetic product carries an approval the blend lacks. When both meet every listed requirement, compare current product data and price.
Is synthetic blend a fixed percentage?
Do not infer a universal percentage from the front label. Evaluate the exact finished product’s specifications and approvals.
Is expensive oil always better?
No. An expensive incompatible oil is still wrong. Among compatible products, compare relevant product data and total cost rather than brand prestige alone.
Sources
- American Petroleum Institute, EOLCS Motor Oil Guide (2025-04-21): service categories and certification marks, defined by performance rather than base-oil type. Accessed October 1, 2026.
- Chevrolet, 2023 Silverado 1500 Owner’s Manual, p. 340: full synthetic dexos1, SAE 0W-20 for the 5.3L and 6.2L V8. Accessed October 1, 2026.
- Subaru of America, 2023 Outback Owner’s Manual (MSA5M2304C), pp. 562–563: 0W-20 synthetic, 5W-30 conventional top-up rule. Accessed October 1, 2026.
- Ford, 2022 F-150 Owner’s Manual, pp. 572–573: Motorcraft SAE 5W-30 Synthetic Blend, WSS-M2C961-A1, 3.5L EcoBoost. Accessed October 1, 2026.
- SAE International, SAE J300_202405 Engine Oil Viscosity Classification, Scope, viscosity-classification purpose and limits. Revised May 9, 2024; accessed July 27, 2026.
- ASTM International, ASTM D5800-21, Scope, standard test methods for evaporation loss of lubricating oils. Accessed July 27, 2026.
- Shell, Shell Helix Semi-Synthetic Motor Oils, product-specific claims for the named Shell formulations. Accessed July 27, 2026.
- Shell, Shell Helix Ultra, product-specific claims for the named Shell full-synthetic formulations. Accessed July 27, 2026.
