A Scientist Found the Absolute Limit of Oil Viscosity - Here’s What It Means for Your Engine

Every car owner knows that motor oil keeps an engine from turning into a pile of scrap metal. That magic comes down to viscosity, the ability of a liquid to flow without breaking apart under stress. But here’s the thing: scientists have just pinpointed the absolute upper limit of viscosity, a number so mind-boggling it makes honey look like water.

And it’s far beyond anything you’ll ever see on a bottle of 10W-30.

Masaki Yoshida, a geophysicist at Japan’s Ritsumeikan University, published a study in Physics of Fluids that sets the “cosmic limit” of viscosity at about 10³⁰ pascal-seconds. 001 Pa·s. Honey is around 10 Pa·s. A substance at this theoretical limit would flow so slowly that any measurable movement would take longer than the Earth has existed.

In practical terms, it’s essentially a solid, more rock than oil.

Yoshida arrived at this number by combining decades of geodetic data, lab experiments on rock deformation, and simulations of tectonic plate movement. The most viscous materials on Earth aren’t lubricants at all, they’re the minerals that slowly creep beneath continents. For drivers, the takeaway is simple: your engine’s oil viscosity is measured in millipascal-seconds, a tiny fraction of that cosmic ceiling.

The weight on the bottle is derived from tests at multiple temperatures, not from anything near that limit.

So why bother finding an upper bound? For researchers, it replaces the lazy placeholder of “infinite viscosity” used in fluid-dynamics equations. The study also promises insights into high-viscosity non-Newtonian fluids, think ketchup that thins when you shake it, and ancient geologic processes.

But mostly, it’s a reminder that the same physics keeping your pistons gliding also keeps the planet’s crust in motion. No need to worry about your engine reaching that limit, though. If it did, you’d have bigger problems than a check-engine light.