Executive Summary: The U.S. Environmental Protection Agency implemented a rule on May 11, 2004 [QR1] which rocked the construction industry. It has made DEF (Diesel Exhaust Fluid) a household name. What is DEF?

What is DEF? DEF is an acronym which stands for Diesel Exhaust Fluid. It’s a liquid. It’s a mixture of 32.5% urea and 67.5% de-ionized water.

Why do we use it, what’s the problem we’re solving? It doesn’t take a rocket scientist to know that what comes out of the back end of a diesel engine-run machine makes a lot of pollution. That black plume is comprised of solids (particulate matter or PM) and gases not good for our environment or for human inhalation.

The oxides of nitrogen (NOx) are particularly harmful and DEF combined with a catalytic converter greatly reduce this pollutant.

How’s DEF work? The liquid is injected in the exhaust stream after the engine and before the catalytic converter. A thermodynamic reaction occurs and what comes out of the tailpipe is “clean”.

What does DEF cost? You can skip this calculations part and go to The Bottom Line if you like.

Let’s take a D6T dozer from Caterpillar as our example [QR2]:

• Fuel tank capacity: 2 gallons
• DEF Tank: 4.5 gallons
• Fuel consumption rate*: 6.7 gph (gallons per hour)

*Caterpillar’s Performance Handbook, medium load factor, page 20-9.

So, here we go. We fill up the tank and then use it until it’s empty:

Fill the diesel tank with 97.2 gallons of diesel. The fuel burns at 6.7 gph so we have to fill it back up again 14.5 hours later:

97.2 gallons / 6.7 gph = 14.5 hours between fill-ups of diesel fuel

In this 14.5 hours of use, I’m saying we used 3% DEF (I’ve read between 2% and 5%). So, in the 97.2 gallons of diesel fuel, we used 2.9 gallons of DEF:

97.2 gallons of diesel fuel * 0.03 of DEF = 2.9 gallons of DEF

Cost of DEF at www.kellerheartt.com is $239.00 for a 55-gallon drum which is $4.35/gallon ($239.00/55 gallons = $4.35/gallon). So, here’s some more numbers for you:

• Analysis: In 14.5 hours we used 97.2 gallons of diesel and 2.9 gallons of DEF
• DEF Consumption: 2.9 gallons / 14.5 hours = 0.2 gallons/hour of DEF
• DEF Cost: 0.2 gallons/hour * $4.35/gallon = $0.87/hour

The Bottom Line. Every machine, field condition, and operator is different, so 100 people will get 100 different answers. But, this gives you an order of magnitude on cost:

My story. I was recently on site with a contractor in the Pacific Northwest. Besides the obvious comment of DEF being a pain-in-the-you-know-what, their complaint was keeping the reservoir full. The advice from their foremen and mechanic was whatever you do don’t let the reservoir level send an error code. An error code may require clearing by a manufacturer’s mechanic (this costs money!) and even worse, the fact that the reservoir went near empty does wear on the machine.

Their advice: always top off the DEF tank!