Sounds like your heatsink is not making full contact with the CPU. You should take it apart clean off the old thermal compound then reset it with some fresh compound. While you have it off get all the dust out of it if it is dusty.
I'm thinking heatsink also since we do not know which brand or what its thermal design is but before you purchase, please ensure you have applied the thermal paste properly (too much can cause high cpu temps also) and that the retension mechanism is installed properly.
If it is a stock Intel or even a lot of the aftermarket ones they have those dumb pins which can be a pain to get in. Sometimes one corner will not click totally and this will make your temps go crazy. Also another good idea is to pull the heatsink and look at the thermal compound make sure that it is makeing 100% contact. If you still have a problem with it after all that then its time for a new heatsink fan.
Last quick question what kind of cooling does the rest of your case have?
Thermal monitor comes in two flavours.
Thermal monitor 1 can adjust the fan speed automatically.
Thermal monitor 2 works in a similar fashion to EIST and reduces the core voltage and/or CPU multiplier when the temperature goes out of specification to avoid permanent damage to the CPU.