About 40 years ago I had a ten year old 4.2 XJS Jag and me and Mrs Mottie-to-be were going to the isle of wight when the clock was coming up to 100,000. I thought it would be cool to be doing 100mph at that point so I got to 100 and held it there. As the odo went on to 100,000 the car filled with smoke so I came to a pretty rapid stop thinking it was an electrical fault. It turned out that the cam cover gasket had blown, probably caused by excessive crankcase pressure, spewing oil onto my exhaust manifold. Gave me a fright though!