Hi folks! Just developed a pretty serious issue:

My 240 (150k) and I were heading down the hwy yesterday when a mean tapping sound started coming out of the engine - not the usual valves-a-little-out-of-adjustment sound, rather more like my valves had been replaced by marbles. It came on quite suddenly. I pulled off at the closest exit and made it to the bottom of the ramp before the car died. I restarted it (a little slower to catch than usual) and it ran essentially normally, though perhaps a little louder than usual. Also, the temp guage was up about halfway between normal and redline, but dropped down to normal within a couple minutes. At idle it acts and sounds completely normal but does seem a little shakier than usual on acceleration.

Anyone have some thoughts? I've lately heard a bit of tap on uphill acceleration, figured my valves were out of adjustment. The oil light was never on and I changed my pump a few thousand miles ago just as a precaution. I'm not driving but the car does start, run and behave basically normally. So... what to check?

Thanks!

-Alex