Screenshot 1 - 28 minutes of Full HD Youtube content, and not a single CPU throttling (I wanted to say victory!)

There was barely some dust on the heatsink that was gone with just a simple air blow, and here are the performances.

I've listen to your advice, and open the laptop.

The Intel HD Familly video card is on-board, just like the nVidia Quadro one, so I will replace the motherboard with the nVidia Quadro model. The P9900 (3.06Ghz), is the most powerful, with just more 10W TDP. I can replace the CPU with 3 other Intel models with the same soket as mine (2.7Ghz/2.9Ghz and 3.06Ghz model). Would this make a good combination and solve my problem? The P8400, is always at 70-90% utilization on Youtube 1080p videos, and I think it's a little bit weak for such intensive task or multitasking in general. I've got the best price possible for a swap with the P9900 3.06Ghz 6MB cache CPU and a nVidia Quadro NVS 160M motherboard. My CPU is a Intel Core2Duo, P8400 2.27Ghz CPU. The idle temp is 42-43 degrees, and the fan is barely running, 44-47 degrees with normal running, and only on Full HD Youtube videos it goes to 50+, and as soon as it hits 52, it goes into CPU throttle, and as I hear it, the fan is around 80% speed (very noisy). I still got the CPU throttling around 52 degrees, and it goes back to normal when it hits 45-46 degrees, and the fan is running at full speed. This thing has been a problem since I've bought the laptop from someone, and by replacing the thermal paste and blowing out the dust from the heatsink, I've made a small improvement (from 6-7 minutes of Full HD Youtube content, to 10+ of Youtube Full HD content), so the problem is somewhere else. Yes, I've downloaded OpenHardwareMonitor, and reading are 100% accurate, just like RealTemp read. Thank you for your reply your help means very much to me.

Dell laptop latitude e6500 driver