If you’re a driver of A Certain Age like I am, you may remember that, back in the day, car engines used heavier oil. You’re not imagining things here, this isn’t some kind of Mandela Effect thing where we’ve always used 5W-20 despite you remembering otherwise. For decades now, automakers have been recommending lighter and lighter oils for new car engines. Used to be that, back in the day, you’d top up with 10W-30 or the old reliable 10W-40 at an oil change, just like granddad used to do. These days, however, you have big, tough pick-em-up trucks like the Ford F-150 calling for 5W-20 and common sedans using super light 0W oils.
So, what gives? Why are engine oils so thin now? It’s not some grand conspiracy or anything, but it is kind of a long and technical answer. The use of thin modern oils comes from a combination of things, but primarily tightening emissions standards and other auto regulations, better and more efficient engine designs, and smarter chemistry underpinning motor oil production. There’s more to it, of course, but that’s a pretty decent précis.
If you’d like to know more, (and why wouldn’t you?) feel free to read on. We’re going to get pretty deep into nerd territory here, but I reckon you’re up for it if you’re reading Jalopnik.
High tech, low viscosity
First off, let’s talk about emissions. Since Corporate Average Fuel Economy (CAFE) standards were put into effect in the ’70s, automobile engines have gotten steadily cleaner, more powerful, and more efficient. Modern 21st-century engines may as well be Hoersch-Kessel ion drives compared to the cast iron lumps that Detroit was putting out in the Ford and Carter years. These high-tech mills run thinner oil because it contributes to lower emissions, which helps automakers meet ever tightening regulations.
As for efficiency, that’s simple. Heavy oils are thick oils, and thick oils require a lot of energy to move around. As fuel economy regulations tightened, automakers looked for more ways to improve efficiency and add another mile-per-gallon here and there. One way to do that is by using a low viscosity oil. The less energy an engine uses to lubricate itself, the less gas it uses in the process. There’s also the fact that as engine technologies and materials sciences have improved, tolerances have gotten tighter and oil passages have gotten smaller. Lightweight oil flows more easily and can get into all the nooks and crannies inside an engine easier than, say, 10W-40.
Finally, there’s the question of quality. Modern oils, especially synthetics, are just plain better than they were 10, 20, or 30 years ago. Reductions in metal-based anti-wear additives and overall improvements in both the base oils and the chemistry behind all the additives that are in them mean that lighter viscosity oils provide the same amount of protection and lubrication as older, heavier oils. They also perform better at higher temperatures and break down more slowly. It’s no wonder that cars have long oil change intervals these days.
Basically, modern cars use lighter, lower-viscosity oils because they can. Because engine technology and petrochemical sciences have improved to the point where they now do more with less while being cleaner and more efficient, which doesn’t suck.
