As summer temperatures rise, should you switch to "summer engine oil"?

The weather is getting hotter, and summer is approaching. The high-speed operation of the engine generates more heat, and as temperatures rise, the viscosity of the engine oil decreases, leading to insufficient lubrication, which exacerbates internal mechanical wear. Therefore, when selecting engine oil for summer, special attention must be paid to viscosity. Choosing the wrong oil can easily result in low oil pressure and, in severe cases, damage the engine.

But at some point, the industry began circulating a claim: only high-viscosity engine oil can truly provide lubrication and protection under high temperatures.

Here, I can responsibly tell you: this statement is wrong!

Switching to higher viscosity oil during seasonal changes is one of the key maintenance tasks for car owners in summer.

High summer temperatures can cause engine oil to become thinner than usual. High-viscosity oil forms a better protective film to prevent rapid loss, ensuring normal oil flow while effectively avoiding localized overheating, oil leaks, and wastage. This enhances both production efficiency and safety.

For example, comparing 0W-20 engine oil to 0W-40, at high temperatures, 0W-20 is thinner while 0W-40 is more viscous. Thinner oil flows better, reduces machine operation resistance, and saves fuel; however, due to its thinness and lack of viscosity, the oil film formed is relatively thin. Under high-temperature and high-shear conditions, the oil film is prone to rupture, causing direct contact between some metal parts of the engine, increasing friction resistance, and potentially leading to engine failure. In contrast, higher viscosity oil has the opposite characteristics: greater resistance, higher fuel consumption, but a thicker oil film with better coverage. Even under high-temperature and high-shear conditions, the oil film is less likely to rupture, providing superior protection.

Therefore, replacing with higher viscosity oil at high temperatures does not seem theoretically incorrect.