I drove my old 2CV without any oil in after my sump plug fell out. Lord knows how many miles I did, but the engine just got hot and power dropped off, so I stopped and called the AA. The nice man told me I'd probably farked the engine well and truly, but a new plug and new decent oil and it ran - better than ever had before, it was like chalk and cheese - much smoother and peppier. I'm not advocating it as a tuning method though...
