Is Higher or Lower Engine Oil Viscosity Better?

[DiKimberly]

There is no definitive answer to whether higher or lower engine oil viscosity is better. The viscosity of engine oil should be selected based on the vehicle model. As a type of machinery, engines have specific requirements for lubricating oil that share common aspects with general machinery, such as the need for appropriate viscosity, certain anti-oxidation, anti-wear, anti-corrosion, and viscosity-temperature properties. Below is an introduction to engine oil: 1. Composition of engine oil: Engine oil is the lubricating oil used by engines, consisting of base oil and additives. 2. Density and functions of engine oil: The density of engine oil is approximately 0.91×10³ (kg/m³), and it serves functions such as lubrication and wear reduction, auxiliary cooling, sealing and leak prevention, rust and corrosion protection, and shock absorption.

[DeSienna]

I've been driving in the southern region for years, where high temperatures are constant. Using high-viscosity oil is more reliable in such hot climates. My old car has run 150,000 kilometers, and I've always used 10W-40 oil—its thicker oil film performs better in high temperatures, especially during summer traffic jams when the engine temperature soars. The high-viscosity oil provides solid protection for the engine. However, last year I switched to a new car, and the manual explicitly recommends 0W-20 low-viscosity oil. At first, I was worried it might be too thin, but I found that it lubricates the engine instantly during cold starts, and my urban commuting fuel consumption dropped by 0.8 liters. A friend from the north told me they always use low-viscosity oil in winter—even at -30°C, the engine starts right up. So, there's no one-size-fits-all answer here. It depends on your driving environment, the age of your car, and the engine characteristics. For older cars in hot regions, high-viscosity oil is the way to go, while newer cars generally perform best with low-viscosity oil.

[SanCarlos]

When I first started playing with cars, I was also confused about oil viscosity. Later, a seasoned mechanic told me the key is to consider the driving scenario. I often drive on mountain roads hauling cargo, with the engine running under high load for long periods. After switching to 5W-40 high-viscosity oil, I clearly noticed the engine sound became more solid, especially when climbing steep hills—no more metallic dry grinding hisses. But for friends who mainly use their cars for city commuting, lower viscosity 0W-30 is more cost-effective, saving a lot on fuel during morning rush hour traffic. Last week, my neighbor’s new hybrid could only use 0W-16, with the manual emphasizing that thicker oil might clog the precision oil passages. My advice? Check the engine model. Older German cars generally suit 40 viscosity, while newer Japanese models usually do fine with 20 viscosity. The factory settings know your car best.

[AmaraLee]

Oil viscosity is essentially a technical choice that balances lubrication and fuel consumption. I conducted actual tests: using 5W-30 and 10W-40 in the same car model, the former showed 200 RPM faster cold start speed and about 5% lower fuel consumption for short commutes, making it particularly suitable for school runs. However, the advantage of higher viscosity becomes evident on highways, with more stable oil pressure after two hours of continuous driving. Nowadays, new cars generally lean towards lower viscosity, like my turbocharged car which came factory-fitted with 0W-20, especially as environmental regulations become stricter. But extra caution is needed for cars over eight years old—engines with excessive wear require higher viscosity to fill the gaps, otherwise, oil burning can easily occur.