I have unlocked CPU and during Doom whole device gets really hot, inclusive bottom part where I would expect battery.
After opening it I've realised that CPU has nice heatstick, but there is 1mm gap between it and top of the case. The heat spreads trough whole device and there is no efficient way to lead it outside.
I've applied 1mm thick thermopad on heatstick, so that now it has direct contact to the top of the case. Now top of the case gets really hot, bottom is only warm.
CPU temperature has dropped by about 5-10 degrees and whole case is just cooler.
Just remember to cut thermopad to small peaces, because 1mm it's a bit thicker then space between heatstick and the case. This extra space between termopads will allow them to squeeze so that the do not apply extra pressure on mainboard and still reman in contact to the case.