Choosing between 0W40 and 5W40 can feel confusing because both engine oils share the same operating viscosity. Many drivers assume they perform the same in every situation. In reality, each oil behaves differently during a cold start. That difference affects oil flow, engine lubrication, and long-term wear. Selecting the correct viscosity helps protect the engine and supports consistent performance in different climates.
The main difference lies in the first number before the letter “W.” A 0W40 oil flows faster at low temperatures than a 5W40 oil. Faster circulation allows critical engine parts to receive lubrication sooner after startup. As a result, engines experience less friction during cold weather. Once the engine reaches normal operating temperature, both oils provide the same SAE 40 viscosity and deliver a similar level of protection under heavy loads.
However, viscosity alone should never determine your decision. Your vehicle’s manufacturer, local climate, engine design, and driving habits all influence the best choice. This guide explains the differences between 0W40 and 5W40 in simple terms. You will learn how each oil performs in cold and hot weather, whether they can replace one another, and which viscosity grade suits your vehicle best.
What Is the Difference Between 0W40 and 5W40?
The main difference between 0W40 and 5W40 is their low-temperature viscosity. A 0W40 engine oil flows more easily during cold starts, while a 5W40 oil remains slightly thicker under the same conditions. Both oils meet the SAE 40 viscosity requirement once the engine reaches its normal operating temperature. As a result, they provide similar protection against heat, friction, and heavy engine loads after the engine warms up. The distinction primarily affects how quickly the oil circulates immediately after startup.
The numbers in an SAE viscosity grade describe how an engine oil performs at different temperatures. The first number, followed by the letter “W,” represents winter performance. A lower number indicates better fluidity in cold weather. Therefore, a 0W40 oil reaches critical engine components faster than a 5W40 oil during cold starts. Faster oil circulation reduces the amount of metal-to-metal contact that occurs before full lubrication develops. This advantage becomes more noticeable in regions that experience freezing winters or frequent low temperatures.
The second number represents the oil’s viscosity at normal engine operating temperature. Since both products carry a 40 rating, they maintain a similar oil film thickness after the engine warms up. This stable oil film protects moving parts from excessive wear and helps the engine operate under demanding conditions such as highway driving, towing, or high-performance use. In other words, neither oil provides a thicker protective layer than the other once the engine reaches its designed operating temperature.
Although many drivers compare 0W40 and 5W40 as competing products, neither viscosity grade is universally better. The right choice depends on the manufacturer’s specification, the climate where the vehicle operates, and the engine’s design. A vehicle engineered for 0W40 benefits from improved cold-start lubrication, while an engine designed for 5W40 continues to perform reliably in moderate climates. Following the recommended viscosity remains the most effective way to maximize engine protection, fuel efficiency, and long-term reliability.
Is 0W40 or 5W40 Better for Cold Weather?
0W40 is the better choice for cold weather because it flows more quickly at low temperatures and reaches critical engine components sooner after startup. Faster oil circulation reduces friction during the first few seconds after ignition, which is when most engine wear occurs. This characteristic makes 0W40 a preferred option for vehicles that operate in freezing climates or experience frequent cold starts.
Cold starts place extra stress on an engine because the oil has not yet formed a complete lubricating film around moving components. As the engine begins to run, the oil pump must deliver lubricant to the crankshaft, camshaft, valve train, and turbocharger if equipped. A lower winter viscosity allows this process to happen more efficiently. Since 0W40 remains more fluid than 5W40 at lower temperatures, it reaches these components faster and helps reduce startup wear. Drivers who regularly park their vehicles outdoors during winter often benefit the most from this faster oil flow.
A 5W40 engine oil also performs well in cold conditions, but it requires a slightly higher temperature before reaching its optimal flow characteristics. In regions where winter temperatures rarely fall below freezing, the difference between the two viscosity grades becomes much smaller during everyday driving. Many vehicles continue to operate reliably with 5W40 throughout mild winters because the oil still provides effective lubrication after the initial startup period. For this reason, many manufacturers approve both viscosity grades for the same engine, depending on the expected climate.
Climate should always be considered alongside the manufacturer’s recommendation. Drivers living in northern regions with long, harsh winters generally gain greater benefits from 0W40. Those in moderate or warm climates may notice little practical difference between the two oils during cold starts. Selecting the viscosity specified in the owner’s manual remains the safest way to ensure reliable lubrication, consistent engine performance, and long-term durability under local weather conditions.
Which Oil Performs Better in Hot Weather?
Neither 0W40 nor 5W40 has a clear advantage in hot weather because both oils provide the same SAE 40 viscosity at normal operating temperature. Once the engine reaches its designed temperature, both lubricants form a protective oil film with similar thickness. This oil film separates moving metal surfaces, reduces friction, and helps prevent excessive wear during daily driving and high-load conditions.
High temperatures place additional stress on engine oil because heat accelerates oxidation and reduces lubrication quality over time. A high-quality 0W40 and a high-quality 5W40 both resist thermal breakdown while maintaining stable viscosity under demanding conditions. As a result, either oil can protect the engine during highway driving, heavy acceleration, towing, or extended periods of high engine speed. The viscosity grade alone does not determine heat resistance because the base oil quality and additive package also play a significant role in long-term performance.
Modern synthetic formulations further reduce the performance gap between these two viscosity grades. Premium synthetic 0W40 oils often deliver excellent oxidation resistance and maintain strong oil film strength even under extreme engine temperatures. Likewise, premium synthetic 5W40 oils provide consistent lubrication and remain stable during prolonged operation in hot climates. For most passenger vehicles, drivers are unlikely to notice any meaningful difference in engine protection after the oil reaches its normal operating temperature.
Instead of focusing only on outside temperature, drivers should consider the vehicle manufacturer’s oil specification. Many European manufacturers approve both 0W40 and 5W40 because each oil satisfies the required high-temperature protection standards. Choosing an oil that meets the correct API, ACEA, or OEM specification is far more important than selecting one viscosity grade over the other. When both viscosities receive manufacturer approval, climate and cold-start performance usually become the deciding factors rather than hot-weather capability.
Can You Replace 5W40 With 0W40 or Vice Versa?
Yes, you can replace 5W40 with 0W40 or vice versa if your vehicle manufacturer approves both viscosity grades. Many modern engines support multiple oil viscosities because manufacturers consider different climate conditions and regional markets when developing lubrication recommendations. Before switching engine oil, always check the owner’s manual or the official oil specification for your vehicle. Following the manufacturer’s recommendation remains the safest way to maintain engine performance and warranty compliance.
Replacing 5W40 with 0W40 generally benefits vehicles that operate in colder climates. A 0W40 engine oil flows more easily during cold starts and reaches critical engine components sooner. This faster circulation improves startup lubrication and reduces wear during the first moments after ignition. Once the engine reaches normal operating temperature, both oils provide the same SAE 40 viscosity. As a result, drivers usually experience similar protection during everyday driving, highway cruising, and heavy engine loads.
Switching from 0W40 to 5W40 may also be acceptable when the manufacturer lists both viscosity grades as approved options. This choice often suits regions where winter temperatures remain relatively mild throughout the year. However, a 5W40 oil circulates slightly more slowly during cold starts than a 0W40 oil. Although the difference is small in moderate climates, it becomes more noticeable when temperatures drop well below freezing. Drivers who regularly face severe winter conditions should avoid changing viscosity unless the manufacturer specifically permits it.
Drivers should never select engine oil based on viscosity alone. Every engine requires an oil that meets specific API, ACEA, or OEM standards in addition to the correct SAE grade. An oil with the right viscosity but the wrong performance specification may fail to provide the required protection for timing chains, turbochargers, emission control systems, or extended oil change intervals. Choosing an approved engine oil ensures the lubricant delivers the protection, durability, and performance that the engine was designed to achieve.
Which Oil Is Better for Different Types of Vehicles?
The best choice between 0W40 and 5W40 depends on your vehicle’s engine design, operating environment, and manufacturer recommendation. Neither viscosity grade is suitable for every vehicle because engines require specific lubrication characteristics to achieve optimal performance and durability. Choosing the correct oil helps maintain efficient lubrication, reduces engine wear, and supports long-term reliability under different driving conditions.
Modern passenger cars that operate in regions with cold winters often benefit from 0W40 engine oil. Its lower winter viscosity allows the lubricant to circulate more quickly during startup, reducing friction before the engine reaches its normal operating temperature. This characteristic makes 0W40 an excellent option for drivers who take frequent short trips, leave their vehicles outdoors overnight, or regularly start the engine in freezing temperatures. Many European performance vehicles also specify 0W40 because it combines excellent cold-start protection with stable high-temperature performance.
A 5W40 engine oil is commonly recommended for vehicles that operate in moderate or warm climates. It provides dependable lubrication during everyday driving and maintains a strong protective oil film when the engine experiences sustained loads. Many diesel engines, turbocharged vehicles, and high-mileage cars use 5W40 because manufacturers approve this viscosity for demanding operating conditions. Drivers who rarely encounter extremely cold temperatures often find that 5W40 delivers consistent performance throughout the year without compromising engine protection.
High-performance and turbocharged engines deserve additional attention because they generate more heat than naturally aspirated engines. These powerplants rely on engine oil to lubricate the turbocharger, control temperatures, and protect highly stressed internal components. For this reason, many manufacturers specify both the viscosity grade and the required API, ACEA, or OEM approval. Following these specifications is more important than choosing between 0W40 and 5W40 based solely on climate. An approved engine oil ensures the lubricant meets the performance standards necessary for your vehicle and provides reliable protection throughout its service life.
Does 0W40 Improve Fuel Economy and Engine Protection?
0W40 can improve fuel economy during cold starts, but the difference is usually small under normal driving conditions. Its lower winter viscosity allows the oil to circulate more quickly when the engine is cold, reducing internal resistance before the engine reaches its normal operating temperature. Once the engine warms up, both 0W40 and 5W40 perform as SAE 40 oils. At that point, their influence on fuel consumption becomes nearly identical because they maintain a similar oil film thickness and lubrication performance.
Cold-start efficiency plays an important role in overall engine operation because most mechanical wear occurs before the oil fully circulates. A 0W40 engine oil reaches critical components such as the crankshaft, camshaft, and valve train more quickly than a 5W40 oil in low temperatures. Faster lubrication reduces friction during startup and helps the engine operate more efficiently from the first moments after ignition. Drivers who make frequent short trips or regularly start their vehicles in cold climates are more likely to notice this advantage than those who mainly drive long highway distances.
Engine protection depends on much more than viscosity alone. Oil quality, additive technology, and manufacturer approvals have a greater impact on long-term durability than choosing between 0W40 and 5W40. A premium synthetic oil that meets the required API, ACEA, or OEM specification protects against oxidation, sludge formation, deposits, and wear regardless of whether it carries a 0W40 or 5W40 viscosity grade. Selecting the correct specification ensures the lubricant performs as the engine manufacturer intended throughout the recommended oil change interval.
Drivers should focus on using the viscosity grade approved for their vehicle instead of expecting measurable fuel savings from changing oil alone. If both 0W40 and 5W40 meet the manufacturer’s requirements, climate becomes the deciding factor. A 0W40 oil offers a small efficiency advantage in colder environments because it flows more easily during startup, while a 5W40 oil delivers comparable protection once the engine reaches operating temperature. In everyday driving, maintaining the correct oil level and replacing the lubricant on schedule contributes far more to engine protection and fuel efficiency than switching between these two viscosity grades.
How Do You Choose Between 0W40 and 5W40?
The best way to choose between 0W40 and 5W40 is to follow your vehicle manufacturer’s recommendation first, then consider your local climate and driving conditions. Engine oil viscosity directly affects lubrication performance, but it should never override the specifications provided by the vehicle manufacturer. Selecting an approved oil ensures the engine receives the level of protection it was designed to achieve throughout its service life.
The owner’s manual is the most reliable source for selecting the correct engine oil. Most manufacturers specify one or more approved viscosity grades together with required performance standards such as API, ACEA, or a proprietary OEM approval. These specifications result from extensive engine testing rather than general operating conditions. Even if two oils share the same viscosity grade, they may contain different additive packages or fail to meet the required performance standard. Choosing an oil that satisfies every manufacturer requirement helps maintain engine reliability and may also protect the vehicle warranty.
Climate is another important factor when comparing 0W40 and 5W40. Drivers who experience long winters or frequent subfreezing temperatures usually benefit from 0W40 because it flows more quickly during cold starts. Faster circulation reduces startup wear and improves lubrication before the engine reaches normal operating temperature. In contrast, drivers who live in regions with mild winters or consistently warm weather often achieve similar results with 5W40. Since both oils provide the same SAE 40 viscosity at operating temperature, their high-temperature protection remains comparable under normal driving conditions.
Driving habits should also influence your decision. Vehicles that make frequent short trips experience more cold starts than those driven mainly on highways. Under these conditions, 0W40 may offer a practical advantage because the engine spends more time operating before reaching full temperature. On the other hand, vehicles used for long-distance travel, heavy towing, or commercial driving depend more on using an oil that meets the correct manufacturer specification than on choosing one winter viscosity over another. Selecting a high-quality synthetic oil and following the recommended oil change interval will have a greater impact on engine longevity than switching between 0W40 and 5W40 without a technical reason.
Frequently Asked Questions About 0W40 vs 5W40
Is 0W40 thicker than 5W40?
No. A 0W40 engine oil is thinner than 5W40 only during cold starts. The lower winter rating allows it to flow more easily at low temperatures. After the engine reaches its normal operating temperature, both oils meet the SAE 40 viscosity standard. At that point, they provide a similar oil film thickness and comparable protection against friction and wear.
Can I Use 0W40 All Year Round?
Yes, you can use 0W40 throughout the year if your vehicle manufacturer approves this viscosity grade. A 0W40 oil performs well in freezing temperatures while maintaining the same high-temperature viscosity as a 5W40 oil. This combination makes it a suitable year-round option for many vehicles that operate in regions with changing seasons. Always confirm the recommended viscosity in the owner’s manual before selecting an engine oil.
Is 5W40 Suitable for Winter?
Yes. A 5W40 engine oil performs reliably during winter in many regions where temperatures remain above extreme freezing conditions. It provides effective lubrication during cold starts and maintains stable protection after the engine warms up. However, drivers who regularly experience severe winter temperatures may benefit from the faster cold-start flow provided by 0W40.
Which Oil Lasts Longer?
Neither viscosity grade automatically lasts longer than the other. Oil life depends on the quality of the base oil, additive technology, driving conditions, engine condition, and maintenance schedule. A premium synthetic 0W40 and a premium synthetic 5W40 can both deliver long service intervals when they meet the required manufacturer specifications and are replaced according to the recommended maintenance schedule.
Which Oil Protects the Engine Better?
Neither oil provides better protection in every situation. A 0W40 engine oil offers better protection during cold starts because it reaches engine components more quickly. A 5W40 engine oil provides comparable protection after the engine reaches operating temperature. The best protection comes from using an oil that matches both the recommended viscosity grade and the required API, ACEA, or OEM specification.
Can Mixing 0W40 and 5W40 Damage the Engine?
Mixing 0W40 and 5W40 is unlikely to damage the engine in an emergency because both oils share the same high-temperature viscosity. However, mixing different products may dilute the additive package and reduce overall performance. It should only serve as a temporary solution until the engine receives a complete oil change with the correct lubricant recommended by the manufacturer.
Conclusion
Choosing between 0W40 and 5W40 is less about finding a universally better engine oil and more about selecting the viscosity that matches your vehicle’s requirements. Both oils provide the same SAE 40 viscosity at operating temperature, which means they deliver similar protection once the engine reaches its normal working conditions. Their primary difference appears during cold starts, where 0W40 flows more quickly and reduces startup wear in low-temperature environments.
For most drivers, the owner’s manual should remain the first reference when selecting engine oil. Manufacturer approvals, API and ACEA standards, engine design, and local climate all influence which viscosity grade will perform best. Using an approved oil protects critical engine components, supports reliable lubrication, and helps maintain long-term performance more effectively than choosing a viscosity based on preference alone.
If your vehicle supports both 0W40 and 5W40, consider the temperatures you drive in most often. A 0W40 engine oil is generally the better choice for cold climates and frequent winter starts, while a 5W40 engine oil performs equally well in moderate and warm environments. By selecting the correct viscosity and following the recommended oil change interval, you can maximize engine protection, improve reliability, and help extend the service life of your vehicle.