DEF

I don't know which DEF equipped trucks don't have a gauge. The Ford has a gauge that says OK, Less than half, or when it gets around the 500 miles to empty mark it pops up a reminder every time you start the truck. Some idiots put DEF in the fuel tank and that can be a bit of a PITA. :) If you start the truck with DEF in the fuel and call the dealer you could be stuck with a $15000 bill. When I did it, I realized what I was doing before starting the engine so I pumped the tank out and even spent a couple hours to remove and flush it. I left the contaminated fuel sit for a while in a barrel to settle out and then pumped off the top to feed it to my old Duramax. So the episode never cost anything but it was a PITA.