Is Higher or Lower Engine Oil Viscosity Better?

[LaJasmine]

Introduction to engine oil viscosity is as follows: 1. Low viscosity: The lower the engine oil viscosity, the thinner the oil film, the better the fluidity, and the relatively smaller resistance to engine operation; however, its ability to resist shear under high temperature and pressure is weaker. The smaller the number before W, the lower the viscosity at low temperatures, the better the low-temperature fluidity, and the lower the applicable minimum temperature. It is easier to start at low temperatures, and the oil can quickly reach the friction surface after starting, helping to reduce engine wear at low temperatures. 2. High viscosity: The higher the engine oil viscosity, the thicker the oil film, the weaker the fluidity, and the relatively greater resistance to engine operation, but its ability to resist shear under high temperature and pressure is better, helping the friction pair resist wear under greater pressure. The larger the number before W, the higher the viscosity at low temperatures, the worse the low-temperature fluidity, and if used at temperatures beyond its capability, it may result in failure to start. Users should choose engine oil viscosity based on their vehicle's requirements.

[Zara]

I just got a new car and realized that oil viscosity is quite a science. I used to think thicker oil was better for engine protection, but cold starts in winter were really tough. Later, a mechanic told me that while thick oil offers better high-temperature protection—ideal for cars frequently driven at high speeds or hauling heavy loads—for everyday driving, especially in cold northern climates, low-viscosity oil flows better, ensuring smoother cold starts and better fuel efficiency. My old car once ran on 40-weight oil, and fuel consumption noticeably increased by half a liter. The advice for average car owners is to stick with the manufacturer’s recommended grade—if the manual says 5W-30, use 30. It’s hassle-free and reliable.

[VonMariana]

It depends on the situation. Having been in long-distance transportation for over a decade, I've gained some insights. For cargo trucks, using thick oil is correct—they endure high engine temperatures and heavy loads, even handling 50 viscosity. However, family cars are entirely different, especially nowadays when new cars emphasize fuel efficiency, making 20 viscosity oil increasingly common. Last time I changed my car's oil to 0W-20, the acceleration felt noticeably smoother, and the displayed fuel consumption dropped by 0.4L. But be cautious: older cars or those burning oil shouldn't blindly chase low viscosity. Insufficient sealing can actually worsen wear and tear. My neighbor's decade-old car started emitting blue smoke after switching to low-viscosity oil.

[LeNatalie]

Oil viscosity is closely related to seasons, which I deeply understand living in Northeast China. I previously used 40-weight oil, and at -30°C, the starter motor would struggle for a long time. After switching to 5W-30, cold starts became much smoother. However, in summer highway driving, I noticed thinner oil heats up faster – once in traffic, the temperature gauge almost entered the red zone. Now I adjust viscosity seasonally: 30-weight in winter, 40 in summer. Reminder: check the W-rating – 5W has better low-temperature fluidity than 10W, crucial for extreme cold. As for high vs low viscosity? Like down jackets versus T-shirts, there's no absolute better choice – it depends on driving conditions.