So on a very technical level — like, an extreme technicality — an engine will indeed run without oil in it. That said, never actually do such a thing, even as a test or a “joke.”
Without oil, those intricate (and metal) parts will rub and scrape against each other. Often at 50 revolutions per second or more. The amount of friction this can create will start to wear out these moving parts very quickly. Think of it as fast-tracking decades of engine wear and tear, with no maintenance, in the span of a few minutes.
The immense amount of strain will also inevitably cause chips and other bits of metal to flake off, which will start to damage the engine even further as they scrape and grind through the machinery. A video from Engineering Explained that runs the same engine with oil and then without shows that, at best, even if nothing extreme happens, you’re going to end up with damaged parts and metal flakes floating around. At second best, the whole thing will seize up and fail. At worst, and as demonstrated by the HOT ROD Network on YouTube, it can lead to smoke, fire, both, or even an internal explosion.
