I run one of these http://www.thinkgeek.com/gadgets/electronic/8426/ in my Disco II to keep me informed about whats going on in the truck.

Great little device that hooks into the ECM connector and displays all the ECM data. Code reader/clearing, reads all ECM (96 and up) date. Can display up to 4 (example: MPG, RPM, Intake Air Temp, Water Temp) sensors at a time and they can be rotated in and out at the touch of a button.

I love it.

 

I have one also... small and does a bunch

luv mine also!

 

This device is the best way to achieve better gas mileage. Seeing the numbers really helps me to slow down. Off road it is helpful to have the coolant temperature as a number instead of a needle pointing to nothing. This along with driving slower will certainly get you better gas mileage!