Why Do Modern Engines Use Such Thin Motor Oil? Here’s Why It’s Recommended

You’re not just imagining things: today’s engines are using much thinner motor oil than they used to. In fact, more than 70% of new vehicles sold in 2024 specified 0W-20 or thinner oil from the factory… and even lower-viscosity formulations are expected to arrive in the coming years. It’s recommended because modern engines have their internal components manufactured with tighter clearances, more advanced materials and coatings, and lubrication systems designed specifically around low-viscosity fluids.

But that might be concerning to those used to using thicker motor oils. Rest assured, oils such as 0W-16 and 0W-20 are not a compromise in engine protection… so long as they’re what’s recommended. It’s part of a larger engineering shift intended to improve fuel economy and help modern vehicles meet contemporary emissions requirements. Modern manufacturing can make engine parts with tolerances measured in microns. That leaves significantly smaller gaps than those found in older engines, and that means significantly thinner oil. Advanced coatings and hardened bearing surfaces also come with greater resistance to wear, meaning there’s less of a need for thick oil to prevent metal-to-metal contact. Overall, today’s thinner oil comes with a 2% to 4% improvement in fuel economy over something thicker like 5W-30, not to mention faster lubrication during cold starts.

It seems the age-old assumption that thicker oil means greater protection simply doesn’t account for how modern engines are designed. In fact, using thicker oil can come with downsides such as increasing viscous friction and making the oil harder to pump through tight passages. That additional resistance could increase fuel consumption, raise operating temperatures, slow the delivery of oil during startup, even interfere with internal systems such as variable valve timing.

That doesn’t mean thinner oil is always better, though. Older engines might still need thicker oil to maintain an adequate protective film because that’s how they were designed. Your best bet is to just follow the viscosity specified by the manufacturer. 

Of course, it helps to understand motor oil viscosity ratings. The first number in a designation (such as 0W-20) describes cold-temperature flow. The lower number indicates that the oil moves more readily in cold conditions. Meanwhile, the second number describes viscosity at normal operating temperature. So, with that in mind, 0W-16 would be thinner than 0W-20, while 0W-20 would be thinner than 5W-30. This should help you get a better idea what you need.