DEF refill

The reason the inside of the exhaust is clean and you don't get the typical diesel exhaust smell is due to the DPF trapping soot particles, not DEF.

I use 1 gallon per 1000 miles of towing. Don't know what it would be not towing because the majority of my miles are towing.

Running a DEF tank dry is not a good thing to do, as mentioned above. I get my first dash message that the tank is getting low at about 900 miles remaining in the tank, then the next message at a bout 500 miles and then one at about 250 miles of DEF remaining. I have never let it get below the last figure. On vacation I carry an extra 2 1/2 gallon jug of the stuff. It is available at most auto stores, the big box stores, and at most dealers (they tend to be the most expensive) Two of the most popular brands I see are put out by Peak and Fleetguard ( a Cummins owned company) and all I have used works fine.

I really like the DEF to cut back on air pollution, as our previous truck was a 2002 Dodge Cummins and it put out a diesel exhaust stink comparable to an old Jimmy 2 stroke diesel. Stop at a stop light in the old Dodge and sometimes the stink of the burned diesel would drift into the cab or into the AC system and it was not pleasant. With the DEF, the inside of my truck exhaust pipe, after 20,000 miles is still as clean looking as it was the day I brought the new truck home. You can stand behind the truck with the engine running and there is zero diesel exhaust smell. To me a cheap price to pay for what the DEF provides.

If the tank runs dry on a GM product it will limit you to 5mph. Dont know about the other brands.

So what happens if the tank runs dry?

2012 F250 and about same, 1,100 miles to the gallon

1000 mpg seems to be the norm in mixed use. If you tow heavy, I've heard it dropping down to 500 mpg for the hard core towing guys.

My 2011 Chevy uses about a gallon per 1,000 miles of mixed driving, empty and towing.

I have a 2013 Silverado 3500. I was told to expect 5000miles on the 5gal DEF tank. I filled it with ~3.5gal at about 4000miles, and added another 4gal when it said I had <1000mi left around 7K on the odometer. I'm currently at 10,000. I think I'm getting around the 1000mi/gal as advertised, maybe slightly better.

I have a 2012 RAM 2500. Never touch the stuff.