Couple good utilities for your D810:

Click {here} fanGUI is a graphical Windows application to show the internal temperatures on the Dell

Recommend running in "Observer" mode to see how your BIOS controls your fans operation.

SpeedswitchXP is a small applet that sits in the system tray and allows dynamic switching of the frequencies of mobile Intel

This will not just give you better CPU Speed control, but provides the best Power Management Profile
Control.

If anything, you should run cooler when not on Power Supply (depending on profile set) and card device
should not create that much heat.

Monthly cleaning will get rid of the lint and dust that is drawn in by your fans and blocks and coats
your cooling fins and vents. A houshold vacuum cleaner, along with clean, dry compressed air (or you
can use the canned 'air' aerosol, sold in electronic, department stores).

I tried both of those, put it still cuts off after 5 to 10 minutes. I thought it was the Nextel wireless modem cards, but it does it without the cards when they are not hooked to the power adapter.

Can I query how long the overheating problems are generally taking? I have a D810 here which after 4 to 6 hours starts to generate odd error messages and then Blue Screens.