5W30 is thicker than 5W20 at typical engine operating temperatures. The second number (30 vs 20) indicates how viscous the oil remains when the engine is hot, with the higher number meaning a thicker oil.
Oil viscosity ratings can be confusing, but they follow a simple two-number system. The first number with the W stands for cold-start performance, while the second number reflects viscosity at the engine’s normal operating temperature. Always follow your vehicle manufacturer’s specification when choosing an oil grade.
Understanding viscosity ratings
Before delving into practical implications, here is how the two-number system works and what it means for thickness across temperatures.
The “W” designation indicates Winter (cold-start) performance. The second number represents viscosity at 100°C, which correlates to engine-operating conditions. Therefore, 5W20 is thinner at hot operating temperature than 5W30, even though both start similarly when cold.
Key differences at a glance
These are the practical distinctions drivers notice in everyday use.
- High-temperature viscosity: 5W30 is typically thicker than 5W20 once the engine reaches operating temperature, offering more film strength and protection under heat.
- Cold-start behavior: Both oils share the same 5W winter rating, so their cold-flow characteristics are similar at typical winter temperatures; actual flow can vary by formulation, but neither is designed to be significantly slower to start than the other at typical cold starts.
- Impact on fuel economy and protection: 5W20 is often chosen to maximize fuel economy and reduce friction in modern engines under normal driving; 5W30 provides greater protection under hotter climates or engines that run hotter or under heavy loads. The effect on MPG is usually small and engine-specific.
In short, 5W30 is thicker at operating temperature, while both behave similarly during cold starts. Always follow the vehicle manufacturer’s specification to avoid warranty or lubrication issues.
Choosing the right grade for your engine
To determine the correct oil grade, consult the owner's manual and consider your climate, driving style, and engine design.
Guidance for decision-making:
- Check your vehicle's manual or oil-filler cap for the recommended viscosity (for example, 5W-20 or 5W-30).
- Consider climate and driving conditions: hotter climates or engines under heavy load may benefit from a higher hot-viscosity grade like 5W30.
- Consider OEM specifications and certifications (API/ACEA) and any warranty requirements.
If in doubt, have a qualified mechanic confirm the best choice for your car and regional conditions.
Summary
5W30 is thicker than 5W20 when the engine operates at normal temperatures. The W rating governs cold-start behavior, which is similar for both grades, while the second number (30 vs 20) indicates hot-weather viscosity. Always follow the manufacturer’s recommended grade to ensure proper protection, efficiency, and warranty compliance.
What motor oil is thicker than 5W20?
The main difference comes once the engine warms up: 5W20 remains thinner, while 5W30 offers thicker protection under heat and stress.
What happens if I use 5W30 instead of 5W20?
The 5W-20, however, will remain a little thinner once you reach operating temperature to help improve fuel economy and flow fast enough to fill the tight tolerances in the engine. Using 5W-30 instead can reduce fuel economy and impede flow throughout the engine.
What are the benefits of using 5W20?
Thinner oil, like 5W20, flows faster, reducing friction and wear during start-up and also improving fuel efficiency by reducing engine drag.
Is 5W-20 or 5W-30 better for high mileage?
Key Differences: 5W30 vs 5W20
5W30 offers better high-temperature protection. It's great for towing, highway driving, or older engines, especially for drivers in Frandor and Lansing who use their vehicles for more than just errands. 5W20 is thinner and generally suited for newer engines that prioritize efficiency.