Difference Between 0W40 and 5W40 | Cold vs. Heat Performance

0W-40 engine oil flows at temperatures as low as -35°C, while 5W-40 is rated to -30°C — the only real difference is cold-weather performance.

Choosing between 0W-40 and 5W-40 engine oil is simpler than most people think. The difference between 0W40 and 5W40 is almost entirely about how the oil behaves when the engine is stone cold. Once the engine reaches operating temperature, both oils protect identically. That is not a guess — it is written into the SAE J300 viscosity standard that governs every bottle on the shelf. Here is what the numbers actually mean and how to pick the right one for your car.

The Cold-Weather Difference

The “W” in both oils stands for Winter, and it measures how well the oil pumps and cranks in extreme cold. 0W-40 is tested down to -35°C for cranking and -40°C for pumping. 5W-40 is tested to -30°C for cranking and -35°C for pumping. That 5-degree Celsius advantage is the entire engineering difference between them. Below those limits, the oil becomes too thick to protect engine bearings during startup.

To hit that lower cold rating, 0W-40 uses thinner base stocks and more viscosity modifiers, which makes a fully synthetic formulation necessary. 5W-40 can be semi-synthetic or fully synthetic depending on the brand, and its thicker base stock gives it better innate shear stability under sustained heavy loads.

Heat Performance and Shear Stability

At 100°C, both oils share the exact same kinematic viscosity range of 12.5–16.3 mm²/s. The High-Temperature High-Shear (HTHS) rating is also identical at 3.5 mPa·s minimum at 150°C. That means your engine sees the same oil-film thickness and bearing protection during normal driving regardless of which grade you choose.

The trade-off emerges under sustained stress. 0W-40 relies on more viscosity modifiers to stretch between its cold and hot ratings, and those additives can shear down over time in high-heat, high-load conditions like track sessions, heavy towing, or desert driving. 5W-40 starts with a thicker base stock and needs fewer modifiers, so it resists permanent viscosity loss better under those same extreme conditions.

Which One Should You Choose?

The answer comes down to your climate and your engine’s demands. If winter temperatures in your area routinely drop below -30°C — common across the northern US, Canada, and high-altitude regions — 0W-40 is the right call. It delivers oil to turbocharger bearings and cam journals faster on a frigid startup, reducing the single most damaging wear event an engine faces.

For moderate to warm climates where winter lows stay above -25°C, 5W-40 provides all the cold-flow protection your engine needs while offering better long-term viscosity stability. It is also typically less expensive per quart. For modern turbocharged engines, our tested picks for 0W-40 supercar oil cover the premium synthetics that meet the latest OEM specifications from Porsche, Mercedes-AMG, and BMW M.

Always check your owner’s manual before buying. Some European engines require 5W-40 to maintain proper hydraulic timing-chain tension, while many Asian and American turbo engines call for 0W-40 to ensure cold-start turbo lubrication. If the manual lists both grades as acceptable, let your local winter temperatures make the final call.

Per the SAE J300 standard published by the Society of Automotive Engineers, both oils meet the same hot-viscosity grade and the same shear-protection minimum. Cartips Daily’s breakdown of the SAE J300 spec confirms that the cold-temperature rating is the only measurable difference. If you live where it never hits -30°C, 5W-40 saves money and handles heat better. If you face genuine arctic cold, 0W-40 is worth the premium.