What is DEF?
DEF (Diesel Exhaust Fluid) is NOT a fuel additive and it is NOT put into the fuel tank of the vehicle. DEF is not subject to fuel tax in any jurisdiction as it is not used to propel the vehicle and is not added to any fuel.
What is DEF used for?
In 2010, new diesel trucks had to start meeting lower emission levels (maximum 2 grams per brake HP). The manufactures of new diesel cars and trucks started using what they call a SCR system which is short for Selective Catalytic Reduction. All manufacturers except Navistar have begun using the SCR system
How does DEF work?
It differs from the standard EGR system as the EGR system re-circulates the exhaust back to the engine’s cylinders. A well run DEF system will get you a 5% fuel savings whereas the old EGR system will cost you 3-5% in fuel.
Is everyone using DEF?
Navistar however believes the EGR is still better as you don’t have the hassle of the extra tank, the space and weight of the tank/DEF (weighs a little more than 9 LBS per gallon), etc.
What is it made of?
DEF is a mixture of 32.5% Aqueous Urea (ammonia) and 67.5% de-ionized water.
The urea is a mixture of synthetic ammonia and carbon dioxide. Urea is also used in making plastics, animal feed, fertilizer and cleaning supplies.
Does it look and smell like fuel?
DEF is non flammable and non hazardous. It smells like ammonia. The vehicle has a separate DEF tank which is distinguished by a unique blue colored cap. The opening is 19mm to prevent a standard 22mm diesel pump nozzle from going in. You can not add DEF to diesel or diesel to DEF.
Does DEF freeze?
DEF will freeze at about -11 degrees centigrade but will thaw and will not be affected. A DEF tank on a truck has a small heater coil in the bottom so it melts a small quantity right away when starting out on a cold morning.
How is DEF placed into a tank?
The DEF is "sprayed" into the exhaust system (not the diesel fuel). It is sprayed at a rate of about 2%, although some people will say they can go to 5% (I would not take it past 3%).
When sprayed into the exhaust system it will break the nitrogen oxides down into nitrogen and water, reducing the NOX emissions.
Where and how do you buy DEF?
On average a truck can run about 300 miles on a gallon of DEF. You can buy it at truck stops and some fuel suppliers. It comes in drums, totes, bulk and 2.5 gallon jugs. The USA requires every truck stop to sell the product.
How big is the DEF tank?
A typical DEF tank on a truck is 6-30 gallons.
If you run out of DEF, you will notice poor performance of the engine and eventually the truck will not start.