What are the differences between 30 and 40 oil viscosity?

1 Answers
OliviaLee
07/24/25 4:52pm
40-grade oil has higher viscosity than 30-grade oil. 40-grade oil is suitable for higher maximum temperatures compared to 30-grade oil. 30-grade oil has better fluidity than 40-grade, which can reduce fuel consumption more effectively and dissipate heat from the engine faster. 40-grade oil offers better oil stability under extremely high-temperature conditions in the engine compared to 30-grade. Below are related explanations: 1. Oil grading: The numbers following the oil grade indicate its viscosity specification. For example, in "15W-40, 5W-40," the "W" stands for Winter. The smaller the number before "W," the better the oil's low-temperature fluidity, indicating it can be used in lower environmental temperatures and provides better engine protection during cold starts. For instance, 5W can withstand external temperatures as low as -30°C, while 20W can only withstand -15°C. 2. Letter combinations: Oil grading uses a combination of two letters. The "S" series represents oil for gasoline engines, with specifications ranging from SA to SN (in alphabetical order, but excluding SI). Each subsequent letter indicates improved oil performance over the previous one, with more additives to protect the engine.
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