I filled mine up at 5156 miles and just yesterday after a 1200 mile trip with 8250 on the ticker it didn't quite hold 21/2 gallons. I think mine might be a bit better because my mpg have gone up and in that 3000 or so miles most of those have been road trips.
The book says 5.3 gallons but it'll hold a bit more. The tank is larger than the quoted 5.3to allow for frozen expansion. If you fill until it "burps", it'll be almost 7 gallons....perfectly fine to do that in warm weather. Winter....not such a good idea. You'll burn about a gallon for every ~1200-1500 miles driven, depending on load. More fuel burned equals more DEF burned. 30K miles so far on mine. Believe me DEF is really no big deal at all. Enjoy the truck.
I've topped mine off a couple of times recently for whatever reason. I've had trouble determining when to stop pouring; it tells me by spitting it back all over the place. Anyone come up with a good method to tell that it is full or almost full? TIA!
To maximize driving range and to prevent over filling the tank, wait until the "Exhaust Fluid Range: 1000 miles (approximate)" message appears on the DIC. At this point, add up to 3.5-gal. Do not add more than 3.5 gal of DEF. When using the CC&A DEF fluid with the nozzle properly installed, when fluid reaches the top of the fill pipe, stop filling. Instructions are provided on the bottle for proper nozzle installation. If another source of DEF is being used, when fluid initially reaches the top of the fill pipe, stop filling and do not force additional fluid into the tank.
As " Navyrep1" stated, it is not recommended to fill the tank beyond 5.3-gal. DEF basically behaves like water and will freeze at 12degrees Fahrenheit and will expand. This does not normally cause a problem if the DEF tank is not overfilled. Adding more than the 5.3-gal usable capacity may not allow for DEF expansion when frozen.
Louis
GM Customer Service
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