Alright, this one isn't quite as bad, but it's still bizarre...
I was removing the auxillary cooling fan's temp switch from the passenger-side head. So, I'm reaching under the exhaust manifold, find the hex, slide on a socket and ratchet it off. Now the switch is sitting in my hand, and the threaded part is obviously quite a bit smaller than the 1/2" NPT that the hole in the head is supposed to be. I reach back under and find an adapter. So, I get another socket, and pull out the adapter.
Instantly, my hand is washed with coolant from inside the head. Seems odd, to me, since I was expecting that to happen when I took out the switch. So, I look at the adapter. It's blind-threaded. The hole don't go through.
In other words, this replacement switch that was installed is actually sensing the temperature of the head, not the coolant.
And, the odd thing is... last I looked, blind-tapped plugs like that are more expensive that reducing couplers...
Not as impressive as some of the things that have shown up in this thread, but still has me scratching my head (after washing the antifreeze of my hand, of course
).
Joe