Dell XPS 14 (L421X) overheating issue

First try cleaning out dust bunnies inside. Can blow out with compressed gas and remove some of the access plates to do a better job.

If no help, to inside and make sure the heat sink(s) is properly attached. If it's OK, remove the heat sink(s), clean surfaces and apply new heat transfer paste (Arctic Silver) or new pads. Search the web for procedures and refer to your manuals.

All clean. Thermal paste "Coollaboratory Liquid Pro".

Same issue

Mine started overheating after wind 10 upgrade. Yours as well?

I'm tried with Ubuntu - same results

I've got the same problem. i will try to clean it in couple weeks. I will write you about results if I won't forget. 

Just wondering, do you find your XPS not overheating while unplugged from power supply?

I'm even tried apply liquid metal as thermal paste, but with the same result - 66°C while idle. 

I have the same temps while uplugged from power supply

I'm just going to share my solution which works great on Ubuntu 16.04 LTS.

With these settings below power and thermal management is significantly improved compared to vanilla installation. I'm coming down to 11W usage on battery and up to 6 hours productivity time. Keyboard heat on left side significantly reduced/eliminated when on battery.

ADVICE: Never try to get the GT630 Nvidia chipset to work on Ubuntu with bumblebee or proprietary drivers. It will always cause headache and difficulties removing. Stick to default Nouveau X Org drivers.

As root, edit /etc/default/grub and change the following:
GRUB_CMDLINE_LINUX="acpi_osi=Linux i915.enable_fbc=1 pcie_aspm=force"
GRUB_GFXMODE=1600x900

Update grub by running:
sudo update-grub2

Install i8kmon with:
sudo apt-get install i8kutils

As root, create /etc/i8kmon.conf with the following content:
set config(0) { {- 0}  40  50  40  50}
set config(1) { {- 1}  50  60  50  60}
set config(2) { {- 1}  55  65  55  65}
set config(3) { {- 2}  65 128  65 128}

Make sure it's enabled:
sudo systemctl enable i8kmon.service
sudo systemctl restart i8kmon.service

Install powertop:
sudo apt-get install powertop

As root, create and edit /etc/systemd/system/powertop.service
[Unit]
Description=PowerTOP auto tune

[Service]
Type=idle
Environment="TERM=dumb"
ExecStart=/usr/sbin/powertop --auto-tune

[Install]
WantedBy=multi-user.target

Make powertop always run auto-tune on reboot
sudo systemctl enable powertop.service
sudo systemctl start powertop.service

Reboot your L421X.
sync
sudo shutdown -r now

Known unresolved issues:

Occasionally wifi is not coming back after suspend, then just restart network-manager:
sudo systemctl restart network-manager.service

Enjoy. F. Jonsson