DEF data

Diesel Exhaust Fluid (DEF) is a liquid mix of approximately one-third ammonia (Urea) and de-ionized water. It weighs more than water, and the tanks take up valuable frame space. It can be purchased nearly everywhere, so no need to over spec the volume on a new truck. The fluid is sensitive to heat, being that it contains a high percentage of water. Cold climates do not bother it, engines have a warm-up period where dosing is not required early in the operational cycle, allowing for thaw.

When DEF fluid was introduced into the after-treatment for heady-duty trucks back in 2010, usage was in the 2% range. The manufacture was required to have enough DEF volume on the chassis to support two complete diesel fuelings. For example, if there were 200 gallons of fuel, take that times 2% so that would be 4 gallons of DEF X 2 fill up’s means we’d have to have at least a 8 gallon DEF tank on the truck.  Since then the EPA requirements and engines have changed and today the dosing percentage has increased to 4% +, that means at least 16 gallons of DEF on board.  Today, since DEF is everywhere, the government has relaxed the 2X fill-up requirement, so today many OEs permit a 1:1 fill ratio. In this case you won’t be able to use cold weather components since the dosing rates increase (they are not a steady percentage) in the cold. 

If you’re in an extremely hot environment, and the vehicle has been sitting for more than a couple months, consider changing the DEF. When the water evaporates the concentrated mix can mess with sensors and fault codes.  Additionally, NEVER use the disconnect switches to shutoff the engine, this cuts off the DEF pump with fluid still in it, the only component at risk when freezing is a potential.

Technically, Urea is derived from one of the byproducts of urine. But it is synthetically made, so no cats (or dogs) are ever harmed in the production of the fluid. And now...

---

Believe It OR NOT

A crocodile cannot stick its tongue out. 

Their tongue is attached to the roof of their mouth by a membrane, keeping it positioned inside of the teeth. Incidentally, an alligator can stick out its tongue.