Ever heard of a runaway Diesel?
I had a 1986 For Ranger Diesel (Mitsubishi 4 cyl turbo).
It had a vent hose that ran from the valve cover back to an inlet on the cover for the air filter.
It would sweat oil through that vent and the oil would soak the lower end of the air filter.
The air filters, and every other part for that matter, were expensive for that thing.
I decided instead of buying another filter I would clean the old one.
I washed it in gas, and laid it out in the July sun on the patio for several hours to dry out.
I could still smell gas, but it wasn't wet to the touch at all, so I figured it was OK to re-install.
IIRC, that tach registered a max of about 7k RPM.
When I cranked it up, it immediately pegged the tach and I suspect it would have gone around again if it could.
It was spinning so fast that it sounded more like a jet than a truck.
Of course, turning off the ignition switch did absolutely nothing, so I ducked down as low as I could get in the front seat and waited it out.
I just knew that it was going to fly apart and shred my carport, but it eventually settled down and shut off.
It was a tough and scary lesson to learn, but hilarious in retrospect.