> I don't think anything with mechanical moving parts is going to last that long, with regular usage, and have original parts.
I know of at least two cars with 800k km with original engines. Both GM small blocks (Gen 2, multiport fuel injection so computer-controlled). Neither engine has been opened since they rolled off the floor in the 90s. They’re not particularly efficient (only about 270HP out of 5.7L) but if taken care of, they probably will go forever.
Definitely an exception, though. Very little else on those cars is still original. But it can be done.
There are definitely a few engine designs out there that won the design lottery in terms of longevity. I know a guy that has close to half a million miles on a Jeep Cherokee with the old AMC 4-liter straight six, and the only engine work done other than plugs and wires is replacing the water pump at 250k. I've got ~186k on my Jeep with the same engine, and it doesn't even burn any oil yet.