This has probably been posted here before, but I thought I'd share it anyway. This was a test performed in 1990 that apparently ran for four years. They took a new BMW 325i and ran it day and night, stopping only to change oil, refuel and do routine maintenance. I was impressed by the video, as I own this exact car and I've seen what it looks like under the valve cover. It's worth watching if you've never seen it before, if for no other reason than the rad '90s synthesizer soundtrack!
http://www.mobil1.com.au/performance/miles.aspx
http://www.mobil1.com.au/performance/miles.aspx