It depends on many factors, includes the diesel engine size, driver, DEF system condition, presence of NOx in the exhaust stream. Typically, manufacturers refer to DEF consumption as a percentage or fuel consumption. This can vary from as low as 2% to as high as 10%. So if your engine consumes 100 gallons of fuel, for a 10% DEF consumption, it would have used 10 gallons of diesel exhaust fluid def.

By the way, some car owners are not sure if they need to use DEF for their cars. There are a number of automakers that use or require DEF. Those include Volkswagen / VW, BMW, Mercedes Benz, Peugeot, GM / Opel, Ford, Toyota, Mazda, Ram, Nissan etc. The best way to determine if your vehicle uses DEF is to consult the owners manual, and also use it to determine the DEF filler / tank location, so you can confirm.

It is a fact nowadays that diesel emission legislation is becoming stricter and stricter. One of the pollutants that interest the legislators particularly, is Nitrogen Oxides (NOx). With every new legislation, the maximum acceptable levels of pollutants change.

For example, when we compare the change of the Nitrogen Oxides (NOx) limits between EPA2007 and EPA2013, it went from 1.2g/hp-hr to 0.2 g/hp-hr. That’s a massive decrease of 83%.

To most of us, numbers mean nothing at all. From an engine manufacturer’s perspective however, this means money. Money spent on research to develop a new engine, or modify an existing engine in order to meet the new standards. Both options can cost from a few millions to maybe billions of dollars.

With the current economic climate, companies try to be as efficient as possible on spending their research budget. The fight to reduce NOx without the need to redesign the whole engine has intensified. Since around 2002, SCR (Selective Catalytic Reduction) systems that use Diesel Exhaust Fluid (DEF) made their appearance in the automotive market.