When overclocking the 3rd generaiton Intel® Core™ processors do run hotter but at their normal speeds they they are cool running processors. In the end I have tried to keep the temperatures on my overclocked Intel® Core™ i5-3570K under 80°C when running Prime95.
I have mine at 4.2ghz running at about 34-41c at 70% +-
Thermal Radar is just a set of temperature sensors on the motherboard. The CPU's on-die temperature sensors will be much hotter since they are directly inside heat source, cutting out all the heat flow resistance and dispersion.
I have a full custom liquid loop and run at 70c at full load overclocked to 4.5. That temp range is safe, been running it for two years. If you are looking to overclock, though, you will need to upgrade your cooler.