[RNEMESiS42]

This EXACT thing happened to me a half an hour after I bought my Supra, and began driving it home! All of a sudden the temp redlined and I had to pull over. I could smell burning antifreeze, and see it on the exhaust cover. I drove it for five more minutes, to a rest stop (thankfully it was right there, I was out in the boonies at 12 am). I hitched a ride back home (2.5 hours...) from some random dude, and drove back up there with some friends the next day.
It was that damn cap at the back of the engine, clipped tight, and cracked open. I couldn't figure out what it's purpose was, but I knew it was the problem. I rigged up a new rubber thing and clamp, and I haven't had any problems since, although I check it from time to time to make sure it's on tight.