I'd been on a boat (shared sleeping cabin with family so no masturbation) for a week. We made it back to the harbor, and after turning off all the lights and instruments, and pumping the bilge, it was finally time to turn the engine off.
Stepping into the hot engine room, the door shut behind me, everything on the boat was off except the monstrous diesel engine. Pitch black, the engine room full of mechanical heat and the smell of lubricating oil, I spent almost a minute breathing it in. I reached for the kill switch (a throttle interruptor dial) and when I touched it, the vibration of the engine shot through my fingers and straight to my crotch. I had one of the strongest, wettest orgasms I can remember.
Finally shut the engine off, and had to acknowledge to myself that I'm a fetishist. No denying it after that! Luckily I could pretend my weak knees were the effect of sea legs.