Motor Oil Weights Explained: What the Numbers Mean
Motor oil weights explained through the numbers on the bottle, with 0W-20 and 5W-30 examples from real listings and the specs each meets.
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- 1
Pennzoil Ultra Platinum Full Synthetic 5W-30 Motor9.6/10View on Amazon - 2
Castrol GTX Full Synthetic 5W-30 Motor Oil9.5/10View on Amazon - 3
Valvoline Advanced Full Synthetic SAE 0W-20 Motor9.5/10View on Amazon - 4
Pennzoil Synthetic Blend 5W-30 Motor Oil9.4/10View on Amazon
The drain pan is under the car, the filter is off, and the shelf holds a row of bottles with numbers that all look alike. Motor oil weights explained means reading those numbers: the weight on the bottle tells you how the oil flows when the engine is cold and when it is warm. This guide explains the numbers, the letters after them, and how to match a bottle to the manual.
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Below: what the numbers mean, how the oils here compare, and how to pick a weight for the next oil change.
Pennzoil Ultra Platinum Full Synthetic 5W-30 Motor
A 5W-30 full synthetic with a 20-year, 750,000 mile warranty, made with natural gas for high-performance engines.
Pros
- 20-year, 750,000 mile warranty
- Made with natural gas
- For high-performance engines
- Exceeds API SP and ILSAC GF-6A specs
Cons
- 1 Quart bottle, while the Castrol here comes as a Pack of 6
- No stated change interval
- No stated temperature range
Castrol GTX Full Synthetic 5W-30 Motor Oil
A 5W-30 full synthetic in a Pack of 6 with protection for 10,000 miles between oil changes and a 12 months warranty.
Pros
- 6X better wear protection than industry standards
- 1.3X better sludge protection
- 3X stronger against viscosity breakdown
- Protection for 10,000 miles between oil changes
Cons
- 12 months warranty, shorter than the Pennzoil Ultra warranty
- No stated cold-start flow claim
- No stated deposit defense figure
- Pack of 6 only in this listing
Valvoline Advanced Full Synthetic SAE 0W-20 Motor
A 0W-20 full synthetic with 40% stronger wear protection, 15% better deposit defense and up to 2.5X better heat protection.
Pros
- 40% stronger wear protection
- 15% better deposit defense
- Up to 2.5X better heat protection
- Meets ILSAC GF-7A and API SQ
Cons
- No warranty term stated
- No stated change interval
- 1 QT bottle only in this listing
- 0W-20 weight, so it fits only engines that call for 0W-20
Pennzoil Synthetic Blend 5W-30 Motor Oil
A 5W-30 synthetic blend in a Pack of 2 that keeps engines clean and responsive, with wear protection from a Sequence IVA using SAE 5W-30.
Pros
- Pack of 2
- Keeps engines clean and responsive
- Compatible with engine seals and all conventional oils
- For all car, SUV, light van and truck gasoline engines
Cons
- Limited Warranty with no stated term
- Title says SinglePack and Pack of 2 at once
- No stated API or ILSAC spec code
Motor oil weights explained: what the numbers mean
A multi-grade weight on a bottle has a number, the letter W, and another number, such as 0W-20 or 5W-30. The number before the W covers cold starts, when the engine turns over and the oil has to flow to the moving parts. The number after the W covers the engine at running temperature, when the oil has to hold a film between parts. A lower first number flows easier when cold, and a higher number after the W holds a thicker film when warm.
The letters after the weight are the specs the oil meets. The Valvoline 0W-20 lists ILSAC GF-7A and API SQ, and the Pennzoil Ultra Platinum 5W-30 lists ILSAC GF-6A and API SP. The Castrol GTX 5W-30 lists ILSAC GF-6 and API SP. The Pennzoil Synthetic Blend 5W-30 states wear protection based on a Sequence IVA using SAE 5W-30. Check the manual for the weight and the spec code it calls for.
| Oil | Weight | Type | Spec codes stated |
|---|---|---|---|
| Valvoline 0W-20 | 0W-20 | Full synthetic | ILSAC GF-7A, API SQ |
| Pennzoil Ultra 5W-30 | 5W-30 | Full synthetic | ILSAC GF-6A, API SP |
| Pennzoil Blend 5W-30 | 5W-30 | Synthetic blend | Not stated |
| Castrol GTX 5W-30 | 5W-30 | Full synthetic | ILSAC GF-6, API SP |
The gear for an oil change
The oil itself carries the weight number, so match the weight on the bottle to the weight the manual calls for before you pour.
How to pick a weight
Start with the manual. It names the weight and the spec code, and the bottle has to match the weight and the spec code. The Valvoline here is 0W-20, and the other oils here are 5W-30. See motor oil types for the full range of weights and grades.
Full synthetic and synthetic blend differ in the base oil. The Valvoline, Pennzoil Ultra Platinum and Castrol GTX here are full synthetic, and the Pennzoil Synthetic Blend is the blend here. See synthetic vs conventional motor oil for how they compare.
The change interval comes from the vehicle manual. The Castrol GTX lists protection for 10,000 miles between oil changes, and the other oils here state no interval. Follow the manual for the interval. See motor oil capacity for how much oil the job takes.
FAQ: garage tools
What does 0W-20 mean?
The number before the W covers cold starts, and the number after the W covers the engine at running temperature. The Valvoline here is a 0W-20 full synthetic that lists ILSAC GF-7A and API SQ.
Can 5W-30 replace 0W-20?
Follow the weight your manual calls for. The Valvoline here is 0W-20 and the other oils here are 5W-30, and each lists the specs it meets. A weight change without the manual behind it risks the wrong flow at cold starts and at running temperature.
What is the difference between full synthetic and synthetic blend oil?
Full synthetic oil uses a synthetic base oil, and a synthetic blend combines synthetic oil with conventional oil. The Valvoline, Pennzoil Ultra Platinum and Castrol GTX here are full synthetic, and the Pennzoil Synthetic Blend is the blend here. The blend lists compatibility with engine seals and all conventional oils.
How long does motor oil last between changes?
Follow the interval in the manual. The Castrol GTX lists protection for 10,000 miles between oil changes, and the other oils here state no interval. Change the oil when the manual says so.
What do API SP and ILSAC GF-6 mean?
API SP and ILSAC GF-6 are spec codes that state what the oil meets. The Pennzoil Ultra Platinum 5W-30 lists API SP and ILSAC GF-6A, and the Castrol GTX 5W-30 lists API SP and ILSAC GF-6. The Valvoline 0W-20 lists ILSAC GF-7A and API SQ. Match the spec code the manual calls for.
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