Blow out the dust bunnies inside and make sure the fan is working (run Dell Diagnostics, F12 at the Boot Screen)
XPS M1530, Win 10 CU Pro 32-bit
Inspiron E1705, Win 10 CU Pro 32-bit
Dimension 9100, Win 10 AU Pro 32 bit
Inspiron 660, Win 10 CU 64 bit
Inspiron 3668, Win 10 CU 64 bit
Asus T100 Tablet, Windows 10 CU 32 bit
I don't why it overheats, but it is common with Dell Laptops. The cooling system or fan is not sufficient. It seems that because the laptop is not elevated with legs, the fan gets blocked while laying flat. You should buy a laptop cooling pad. It is like a laptop table with fans. I had a one fan Belkin brand but it stopped working after a few months. It did not have an on/off switch. My newest cooling pad is a Targus Chill HUB XC, it has two fans and four USB ports and an on/off switch. It plugs into the laptop's USB port and runs while the laptop is on. It works much better than the Belkin. I no longer have problems with the laptop overheating. You can buy one at Best Buy.
give the internals of your laptop a clean as dust will build up, if this doesnt work then you may need to dissassemble the heatsink assembly and re apply the thermal paste on the cpu. hope that helps.