Five TIER IV Lessons


If you’re finally running a Tier IV engine in a piece of rolling stock, take heed to the lessons here. If you haven’t quite gotten there yet, choosing instead to squeeze the last Tier III machine out of the last dealer with one, or hanging on to that old machine until it can’t sputter any more, you’re only putting off the inevitable. It’s not that bad to make the switch, if you understand just a few simple things about combining DEF and extra low sulfur diesel fuel.


  • Don’t force a nozzle where it won’t fit
  • Don’t put DEF in the fuel tank
  • Don’t think 1:1 DEF to fuel fill ratios are better than 12:1
  • Don’t use #2 heating oil for fuel
  • Don’t grab a pig and collect its urine, then mix it with tap water to create DEF

These might sound pretty elementary to you, but maybe not to everyone. All of these things have happened, and the outcomes were not pretty. Let’s take them one at a time.


There are 3 major fluid tanks on large rolling stock: hydraulic, fuel, and DEF. For all of these, the caps are different, and the neck sizes have different girth. If the nozzle is too large for the hole, then that’s not what goes in there. If the nozzle has a lot of room to move in there, then that’s not right either. If it fits like a glove, you’ve found the right tank. If I didn’t have the service reports to prove this, I wouldn’t be saying it. DEF is slowly corrosive on a range of metals. If it goes in the fuel tank, it’ll be a slow killer. The engine will run, but it will begin to chatter and knock. Power will wane. If continued to run, the engine could seize. It’s an expensive lesson that could require complete engine replacement.


I’ve heard manufacturers claim a 1:1 or even 3:1 fuel to DEF ratio, like that’s some sort of achievement. Well, it’s not. Or maybe they claim that the competition has a much bigger DEF tank, and therefore they burn more DEF. Well, that’s just a lie. Every Tier IV diesel engine burns between 2 – 3% DEF, meaning that for every 100 gallons of fuel, they’ll burn between 2 – 3 gallons of DEF. A ratio of 5:1, for example, means that for every 5 full tanks of fuel, that engine will burn 1 full tank of DEF. You want that ratio to be as high as possible, because the fewer times the DEF tank is opened for filling, the fewer opportunities there are for contamination. And contamination in DEF is arguably worse than contamination in hydraulic fluid. Ratios of 11:1 or even 13:1 are available.


In the north, where folks use heating oil in their homes during the winter, contractors were known in years past to use the same oil in Tier II and Tier III engines. It was cheaper, and according to them, it worked just fine. However, Tier IV engines can’t handle the composition of #2 heating oil and DEF combined: the result will look a lot like what happens when a large smoke bomb goes off. The engine will run just fine, but the white smoke and long term effects on injectors is like something out of a war movie. For those not in the north who think they’re getting extra low sulfur diesel fuel but can’t understand why the engine smokes so badly, quickly do a fuel test. Take the sample to a source that is not your fuel supplier. Chances are it’s not what you thought you were buying.


Finally, don’t make your own DEF. A mix of pig urine and water will have a similar composition, but it’s rather impure, and pigs aren’t easy to catch—much less their urine. DEF is approximately 33% high purity urea (somewhat like pig urine) and 66% deionized water. When this is heated, it basically turns to ammonia, which is then used to burn off the NOx (nitrous oxide) in your engine emissions for that cleaner exhaust.


Remember to be extra vigilant in training and understanding when getting your first Tier IV engine-equipped machine. Improper fluids—or even improper filling of the right fluids—can have expensive results. And skip the pig urine.