CPU – Is My i7 Running Too Hot?

If the fan is very cool and the processor is reporting very hot, I would first suspect the connection between the fan/heatsink and the processor package. Make sure the heatsink is properly seated with thermal paste.

Let's get some terminology straight from Lavalys' KB:

• CPU Diode or Core temperature is the temperature measured across a temperature sensitive diode on the processor die. The most common implementation uses a temperature sensor part external to the processor with the CPU Thermal Diode Anode (+) and Cathode (-) connections to it.
• CPU Temperature is the temperature measured by a remote temperature sensors part on the motherboard near the CPU.

It is possible for these temperature sensors to fail although I haven't seen it personally.

Try installing a different processor and see if the readings are still incorrect. This can help point to where the problem lies. If the readings are OK, I would suspect your processor, if they are off as well, then suspect the parts on the board.

Unfortunately, if it isn't the heatsink, there is no easy user fix other than replacing the offending part.

There are clear guides from the manufacturers on operating temperatures for the various components in your system. Identify the important ones like CPU, GPU, RAM and Motherboard using something like CPU-Z, then look up the acceptable operating temperature for each component using the manufacturers specifications.

The key thing here though is that you're saying that you've noticed fundamental changes in the way your computer behaves. That's never good and there's usually a root cause that you need to identify to solve this. You probably don't want to be satisfied until you've solved this, even if you're 'within temperature tolerances'.

I'd suggest giving the PC a more thorough cleanout by taking it out to the roadside and blasting it with pretty much the entire can of air, until the motherboard and components look nearly new. You'll want to get into the graphics cooling spaces, around the CPU, around fan bearings, any heatsinks, and any corners where dust accumulates. Ditch the vacuum though, because they produce a static field at the end of the vacuum hose that can fry integrated circuits. Also beware of turning the air can upside down unless it's marked 'invertible' (and the invertible type have way less 'juice', so just use a regular one and keep it upright).

Worst-case, replace the heat compound on the CPU heatsink by following any one of the internet guides on the subject. If you're other component temperatures (GPU, motherboard) are also high though, this probably isn't the root cause of your issue.

BTW any time you're running a PC on a carpet, your dust problem isn't going to go away. Try and elevate it onto a hard surface, and ensure there's sufficient space at the rear of the unit to allow vented hot air from the case to circulate out into the room. Put your hand behind the case after an hour or two and if it feels even slightly warmer than the rest of the room, there's not enough space.