I upgraded my PC's default cooler with the aforementioned Arctic Cooling product, and idle temperatures have doubled to around 85-90 degrees Celsius.
Why would this be?
I used a glob of TX2 paste about half the size of a pea in the center of the CPU heat spreader when I was installing it, and it only twists a tiny bit.
All in all, it should be working fine; it's (supposedly) a good cooler, and it seems to be in right.
I did muck about trying to install it , though, with shenanigans involving pairs of flat-head screwdrivers trying to get the default back[late off.
Could these high temperatures be a result of a damaged motherboard/CPU?
Also, the thermal grease: is it necessary to remove all of it with rubbing alcohol, or does just wiping off the visible bits with a paper towel work?
A little bit of it also slipped between the heat spreader and the frame that covers it; I didn't bother trying to remove it, because I didn't want to take the risk of damaging the CPU itself. Could that be the cause of these problems?
Firstly take it the cooler off and clean it properly removing any and all thermal paste from the previous installation.
Second if it "twists" at all as you have said it twists a little bit that's bad, it means your heat pipes aren't in contact with your chip properly and drawing the heat away. Once you have the old paste cleaned off reapply it and tighten it down so it doesn't move.
Did you scratch your board or leave any visible sign of damage with the screwdrivers?
As Tuilalcaron said, your CPU shouldn't twist or more at all if its properly tightened down.
Apply a good size blob in the middle, a pea is a little "skimp-ish" in my opinion, just don't go crazy so its not being squeezed out of the sides and dropping onto your motherboard and you'll be fine. Tighten the CPU down slowly, doing each corner a little at a time until its on as tight as it will go.
CPU damage or motherboard damage are HIGHLY unlikely if all you did was clean and re-apply. Most likely the thermal paste wasn't applied properly and in combination with the heatsink not being fastened down properly, this is what's causing your higher temperatures.
It's an Arctic Cooling Alpine 11 Pro 2, CPU isn't overclocked at all, and "twist" is perhaps the wrong word; "wobble" is perhaps more accurate. I think it's just the rubbery screw-things that hold the fan guard on.
As for paste, when I installed the stock cooler, I used a slightly larger glob, and it turned out to have spread too much.
The screwdrivers: there was no visible damage or scratching, no, but before I got to that point I was handling the board perhaps more than I should have, trying to get the cooler to fit. I'm pretty sure I may have touched a capacitor or four, and I can't find any information about motherboards that're zapped enough to malfunction, but not enough to die outright.
Right now, according to Speedfan, it's idling at (alternately) ~60 to ~69 degrees. It might just be that the paste takes time to "set"; I wouldn't know, because after I installed the stock cooler (with the same paste) I spent about a fortnight dickering about trying to get the RAM to function; it wouldn't even POST, so I've got no idea if it had heat issues that later went away.
On the screws: I know how you're supposed to install a four-screw cooler, but the one I have only has two screws: http://www.trademe.co.nz/computers/components/cooling-f... so I alternated; I'd tighten the one on the left, then the right, then left again. I'm not sure if it's screwed in all the way, though; the screwdriver started to skip out of the screws, but it might just be that I wasn't pressing hard enough.
EDIT: and then a few moments later, temps go up to the high seventies and mid eighties.