There is a wide variety of motor oil grades available in the market. These different oils have unique properties, viscosity ratings, and performance capabilities. One of the most frequently asked questions is, Is it okay to use oil with different grades than what the manufacturer recommends?
The SAE 15w40 and SAE 20W50 are popular heavy-duty motor oil grades on the market. Although both oils are commonly utilized in engines, their distinct characteristics can impact performance and longevity. When it’s time for a vehicle oil change, many people wonder if they can use 15w40 instead of 20w50.
This article will comprehensively explore the differences between 15W40 and 20W50 motor oils. Furthermore can use 15w40 instead of 20w50 and much more.
In This Article:
Can I Use 15w40 Instead Of 20W50?
Yes. You can use 15W40 instead of 20W50. Viscosity is the main difference between these two oils. At low temperatures, 15w40 performs better, while 20w50 performs better in hotter temperatures. The SAE 15W40 motor oil is thinner compared to the SAE 20W50. Therefore, during a cold startup, the SAE 15W40 flows rapidly and lubricates the engine components.
When using thinner oil, it quickly flows at low temperatures. Moreover, it can improve fuel economy. However, in extremely high operating temperatures, it is quickly thin out than the 20W50 motor oil.
Can I Use 20W50 Instead Of 15w40?
Yes. You can use 20W50 instead of 15W40 motor oils. When using more viscous oils, it is slowly thin out at higher operating temperatures, but it has reduced performance in colder climates. However, in cold temperatures when using 20W50 oil it requires more energy to pump the oils around the engine and oil filter.
If your engine manufacturer recommended 15W40 or thinner oil, it might not give optimum performance if you use 20W50 motor oils. The reason for that is thicker oil flow slowly. Therefore it reduces fuel economy and engine metal parts wear.
What is 15W40 oil?
The SAE 15W40 is a multi-grade motor oil. The 15W is the viscosity in a cold climate, and the 40 is when the engine reaches its highest operating temperature. This grade of oil is made of either mineral oil, synthetic oil, or a mix of mineral and synthetic oils with performance-enhancing additives and viscosity improvers.
What is 20W50 oil?
The SAE 20W50 is a multi-grade motor oil that especially uses for heavy-duty engines. This oil 20W is the oil’s low-temperature viscosity, and 50 is when the engine reaches the highest operating temperature. Like other motor oils, this one is made from petroleum, synthetic, or a mix of petroleum and synthetic base oils.
Difference between 15w40 and 20W50.
Viscosity.
One of the main differences between 15W40 and 20W50 is their viscosity. Viscosity is the oil’s resistance to flow with temperature changes. These oils’ first two numbers (15W or 20W) are the viscosity at cold temperatures. The lower the first two numbers, is lower the viscosity (thinner). Two numbers right after the letter “W” is the viscosity at high operating temperature. Higher the number higher the viscosity (thicker).
Fuel Economy.
The SAE 15W30 is thinner than the 20W50 oil. Thinner oil has better fuel efficiency than the thicker one. Moreover, less viscosity oils easily pump around the engine, requiring less energy.
When the oil gets thinner, it has more viscosity index improvers (Polymers); when the oil temperature increase, polymers molecule entangle. So at high-temperature, oil thinning slowly, so it needs more energy to pump motor oils around the pistons. Thinner oils have better cold-flow capability, so oil easily flows at a lower temperature.
Hot Operating Temperature Performance.
Thicker oils have better performance in hot operating temperatures. However, thinner, fully synthetic oils perform better than petroleum-based motor oils at extremely high operating temperatures due to their even molecular size. Petrolium-based oil has uneven molecules, so when the temperature is raised, their quickly thin out.
If we take the same base oil SAE 15W30 and SAE 20W50 oils, the thickest SAE 20W50 performs better (better protection against wear).
Cold Weather Performance.
Generally, thinner oils have better cold-flow capability than thicker oils. When the temperature gets lower, the oil becomes thicker. In this 15w40 vs 20W50 comparison, SAE 15W40 performs better in cold weather.
Performance.
For better fuel economy and excellent cold weather performance, thinner SAE 15W40 oil is better. However, both of these oils perform well in cold and high temperatures. If you use full synthetic 15W40 motor oils, it is way more advance than petroleum-based motor oils.
We can summarize the difference between 15w40 and 20W50 motor oils below.
| Characteristic | SAE 15W40 | SAE 20W50 |
|---|---|---|
| Viscosity at cold temperature. | Better cold-flow | Slightly less efficient in cold climate. |
| Viscosity at high temperature. | Relatively quickly thin out. | Relatively slowly thin out. |
| Fuel Economy. | Better fuel efficiency | Lower fuel efficiency |
| Hot Operating Temp Performance. | Lower performance | Better performance |
| Cold Weather Performance | Better performance | Lower performance |
| Overall Performance | Better fuel economy and excellent cold weather performance and good performance hot temperatures. | Excellent performance in hot operating temperatures and better performance in cold temperatures. |
| Uses | Light vehicles | Heavy vehicles. |
FAQ.
Can you mix 15w40 with 20w50?
It is not recommended to mix two different viscosity oils together. Various grades of oils have different additives and chemicals. When these are mixed, a new type of oil with a different viscosity grade can be produced, leading to changes in oil performance.
Conclusion.
SAE 15W40 and 20W50 are popular motor oil grades. The best motor oils for your vehicle solely depend on the original equipment manufacturer’s recommendation. Both of these oils have unique advantages and disadvantages.
To avoid any negative consequences, referring to the user manual before trying out a new oil grade is crucial.
