HP :: Pavilion G6 2252so Closing Down Due To High Heat (fan Has Been Cleaned)

I'm trying to repair a G6 model due to heat issues. The laptop is approx. 1 year old. From what I could read from the internet, It's due to dust build up mainly. 've completely cleaned the fan (incl. unmounting the fan cover), and change thermal paste on the CPU. The issue persists. With the program Speccy I read starting temps. for CPU of 90 degrees celsius. It's very different when the laptop shuts down. Sometimes it happens quick, other times it can run for hours. Even if the CPU is completely cold, it can shut down before windows even starts properly up. I manage to see temperatures over 150 degrees celsius which should be alarming high. Even 90 degrees seems VERY high to me. The air blown out from the fan doesn't seem hot. It's only mildly warm and the fan speed adjusts in accordance to the temperature. It starts to go up when going over 100 degrees. At 90-99 degrees it runs fairly slow.

If I try going to the BIOS, I only have seconds in there before the laptop shut down.

From my point of view, it must me either temperature sensors not working properly, or handling of the temperature sensors that's misinterpret, or simply the cooling system that's defect. I'm not sure how the cooling system works. The seating has a cobber pipe the leads to the radiator and fan. Does the pipe contain a fluid? Could the fluid somehow have vaporized?

I've had the cooling system dismounted? I haven't tried updating the BIOS, since I'm afraid I'll brick the laptop, if it shut down during the process.
 
Where is the temperature sensors placed on the board? Is the sensor for the CPU built in or is it placed besides/under it?