Common Questions Answered About Diesel Exhaust Fluid

Are you driving a diesel truck for the first time and therefore just learning about DEF or diesel exhaust fluid? DEF is a non-hazardous solution. It’s made from 67.5% de-ionized water and 32.5% urea. Its purpose is to spray into the diesel vehicle’s exhaust stream. In doing so, it breaks down NOx emissions into harmless water and nitrogen.

How Often Do You Add DEF?

Under most circumstances, between two and four gallons of diesel exhaust fuel automatically injects into exhaust systems when every 100 gallons of diesel fuel is consumed. In most cases, the typical diesel fuel tank’s capacity is between 15 and 20 gallons. Therefore, the tank will need refilling between 5,000 and 6,000 miles.

How Many Miles Does a Gallon of Diesel Exhaust Fluid Last?

In most cases, diesel exhaust fluid tanks require one gallon of fluid for every gallon of fuel. That way, that one gallon will last for between 300 and 500 miles.

Is it Harmful if DEF Runs Out?

The truck will provide ample warning if it is running low and before it runs out of DEF. If it runs out entirely, it will stop working. The same result will happen if it runs out of diesel fuel. The truck won’t run at all. Often, before it runs out entirely, the truck will begin powering down.

Should DEF Go Into the Diesel Tank?

No, DEF shouldn’t be put into the diesel tank. If this happens, it contaminates the diesel fuel. The main reason is that the diesel exhaust fluid is made from water and urea. The DEF should be introduced to the storage tank; otherwise, it could cause damage to the truck’s fuel system.

Is Diesel Exhaust Fluid Required?

As of 2010, using DEF is mandatory in large highway trucks. The main reason is that it helps with the reduction of pollution. Since the mandate was put in place, there’s been a 90% reduction in pollution emitted by busses and trucks.

Can DEF Go Bad?

Yes, but it depends on several variables. Expect DEF to degrade over time, but the speed depends on its exposure to sunlight and the storage temperature. If it’s stored between 10 and 90 degrees Farenheight, then expect it to have a one-year shelf life.