What is the difference between engine oil 20 and 30?
5 Answers
The viscosity of engine oil differs, as does its sealing performance. Below is a detailed explanation of the differences between engine oil 20 and 30: 1. Different oil viscosity: The primary difference between 5W30 lies in the high-temperature viscosity of the oil. The distinction between 5W-20 and 5W-30 is merely the difference in the latter numbers. 5W20 has lower viscosity (ranging between 5.6-9.3), which is relatively more fuel-efficient and provides a lighter driving feel. On the other hand, 5W-30 has higher viscosity (ranging between 9.3-12.5), which is relatively more fuel-consuming and makes the throttle feel heavier, but results in quieter engine noise. 2. Different sealing performance: The higher the viscosity, the better the sealing performance. For engine oils 5W30 and 5W20, the number after the W represents the high-temperature viscosity. Therefore, 5W30 has better sealing performance than 5W20. However, a higher number is not always better, as higher viscosity leads to greater friction and consequently greater power loss in the engine.
I'm the most qualified to speak on this matter, as my car has experienced both types of oil. The numbers 20 and 30 after the W represent high-temperature viscosity—the higher the number, the thicker the oil becomes when the engine heats up. The 20-weight oil has better fluidity, lubricating parts quickly like water during cold starts, making it particularly suitable for new cars. Last time I switched to 20-weight oil on the highway, I clearly felt the throttle become lighter, and the fuel gauge dropped more slowly. However, the 30-weight oil offers better high-temperature protection, giving more peace of mind for older cars. Once, I drove a friend's 8-year-old SUV after switching to 30-weight oil, and the engine sound became noticeably more stable. Which one to choose depends on your car's manual—never switch viscosity based on assumptions.
An experienced car mechanic once told me that the secret to choosing engine oil lies entirely in the viscosity rating. The key difference between 20 and 30 is the high-temperature shear value, which refers to the viscosity performance at 100 degrees Celsius. 30-grade oil is thicker at high temperatures, making it particularly friendly to older engines as it forms a more stable oil film. Most Japanese cars require 20-grade oil, while some German models specify 30. Recently, a customer insisted on using 20-grade oil for their Tiguan, resulting in an engine warning light—you can't arbitrarily reduce viscosity when the manufacturer requires 30-grade oil. 20-grade oil pumps faster during cold starts, allowing smooth starts even at -20°C in northeastern China, while 30-grade is more recommended for consistently high temperatures in southern regions. Remember: choose 20 for fuel efficiency in new cars, opt for 30 for better protection in older vehicles, and always follow the manual for German cars.
From a physical perspective, the main difference between these two engine oils lies in their high-temperature kinematic viscosity. SAE 30 has approximately 3-4cSt higher viscosity than 20 at 100°C, which translates to a noticeable difference in engine resistance when accelerating. My test data shows: the same Camry model consumes 0.7L less fuel in urban driving with 20-grade oil, but when driving on mountain roads, 30-grade oil maintains 5°C lower oil temperature. Remember to check the HTHS value requirement in your vehicle's manual - most modern cars with variable valve timing technology may trigger warning lights if wrong viscosity is used. For example, Corolla's factory specification requires 0W-20; switching to 30 won't cause immediate damage but increases long-term risks of crankcase carbon buildup. Oil selection should consider driving habits - for frequent long-distance trips with full loads, 30-grade provides better peace of mind.
Last month, I just helped my cousin choose engine oil. 20-weight oil is suitable for new cars with precision engines, like his hybrid Yaris that's been running for five years always using 20-weight, consuming only 4.9 liters per 100 kilometers. 30-weight oil is thicker; after my friend's decade-old oil-burning Sylphy switched to 30 viscosity, oil consumption dropped from one liter every 2,000 kilometers to half a liter every 5,000 kilometers. The key is to follow the original manufacturer's certification standards—if the oil cap says 0W-20, never switch to 30. Once, a repair shop mistakenly added 30-weight oil to a Civic, and the valve noise during cold starts was terrifying. Temperature also matters—in northern winters with temperatures below -20°C, 30-weight oil takes several seconds longer than 20-weight for the RPM to drop after a cold morning start.
