Make sure the HSF has all 4 pins snapped in (they don't snap in easy--very stressful to do this). If any are loose, the heatsink won't be tight enough against the processor and thusly, temperatures will be higher. It could have came loose when you were cleaning it.
Also, make sure you have an adequate (not too much, not too little--just enough for a thing layer covering the cores) amount of thermal paste. Arctic Silver's instructions
for apply thermal paste are the best. Follow them to the T.
If it did come loose, you'll probably have to take the HSF out, clean both surfaces with isopropynol alchol, and put it back together with fresh thermal paste. Air pockets are very bad for cooling.
I'd say the thermal sensors are just going bad but thermal sensors wouldn't trigger BSODs. Something is actually causing errors that jeoprodize the stability of the system, hence, BSOD. What are the STOP codes by the way? Also, is there a file listed (e.g. nv4_disp.dll, ntfs.sys, etc.) in BSOD?