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What’s in your DEF tank?

Like any fluid or lubricant used in ag machines, diesel exhaust fluid needs 
to meet manufacturer standards, or you may be in for trouble

fluid storage tank

At first blush it seems like diesel exhaust fluid, commonly known as DEF, isn’t a thing that warrants much thought. After all, it’s just a blend of distilled water and 32.5 per cent automotive grade urea. And all that happens is it gets injected into a chamber in the engine’s exhaust system to react with nitrogen oxides. What could really go wrong?

As it turns out, quite a lot.

Recently, we at Grainews, have heard credible reports that at least one brand of DEF may have caused engine problems for a customer. That prompted us to do a little digging into the topic. We found out that just as you wouldn’t try and save a few dollars pouring cheap oil into the crankcase of a brand new, very expensive, diesel engine, you shouldn’t scrimp with DEF either. There are dangers.

“If you buy DEF that’s not API (American Petroleum Institute) certified, you run the risk of getting a product that doesn’t meet the ISO22241 quality standard,” says Chad Smith, product line marketing manager at John Deere. “Which can result in the engine derating which would lead to down time. We recommend you only buy API certified product to prevent problems with out-of-spec DEF that could cause extremely expensive repairs to the SCR system.”

Despite the simple-sounding formula for DEF, the fluid can suffer from a lot of different problems if accepted standards aren’t followed by the manufacturer.

“With the variety of manufacturers out there, it (DEF) can be produced in a variety of different ways,” explains Brian Schmidt, product engineer for DEF at John Deere. “There is certainly a plethora of things that could be out of spec. Anything from dust and dirt-type contamination, to the product not being on concentration, to random types of urea quality used to blend the product that could lead to contamination.”

“You could get filter plugging. You could get nozzle plugging on the injector of the SCR system. You could get deposits that form inside the catalyst that reduce its effectiveness. You could also get different PH levels, or different elements that cause corrosion within the system. Most on-highway SCR systems use a DEF quality sensor in the tank. Those look primarily for (urea) concentration levels, which could change if water has evaporated off or the fluid has been watered down. They could send a (trouble) code that way. So far, off-highway hasn’t been mandated to use those sensors.”

Urea concentrations higher than 32.5 per cent in DEF could lead to early SCR system component failures.

If a manufacturer uses non-automotive grade urea in the production process, that could be a major problem, too, even if it is blended with good quality water. Ordinary fertilizer-grade urea granules have a coating that contains contaminants that could react negatively with SCR system components when dissolved in the solution during manufacture, and it is usually handled and transported in a way that easily allows for other types of contamination. All of that can cause serious engine problems.

jug of fluid
John Deere recommends using diesel exhaust fluid that meets ISO standards and carries an API certification mark. Deere now offers its own branded DEF, which is available through its dealers. photo: John Deere

“At this time, API is the only organization regulating the quality of DEF in the U.S. and Canada,” adds Smith. DEF that meets the ISO standard and is certified by API will display the organization’s logo.

“It won’t look like the API ‘doughnut’ (found on engine oil containers),” adds Schmidt. “It’s a black square and it will say ‘American Petroleum Institute certified diesel exhaust fluid’. At this time the off-road and on-road (engines) are using the same product.”

If you’re in doubt whether or not fluid on the shelf in your farm shop is certified, you can do a product search on API’s website, or call their help desk at (877) 562-5187.

When buying DEF for ag equipment, Deere recommends farmers not get ahead of themselves by stocking up with excessive amounts just to cash in on an occasional sale. “We recommend purchasing DEF in quantities that can be used within a year to avoid any longterm storage issues,” says Smith. “Certainly try to use up any remaining DEF within 18 months. You want to make sure you keep the containers sealed between use to prevent any contamination or evaporation. And keep the containers out of direct sunlight to prevent any solar heating of the fluid which can reduce the effective life of the product.”

“One thing to note is DEF quality is unaffected by freezing,” he continues. “Upon thawing it may be used without issue. DEF will freeze at -11 C when the 32.5 per cent concentration is maintained.”

If the fluid is diluted with water or concentrated due to evaporation, that freeze point will fluctuate.

So if you’ve cut corners by deliberately purchasing non-certified DEF or you’ve unwittingly been burned by poor quality fluid and run into engine problems, what happens to your engine warranty? “Each one (at John Deere) is handled on a case-by-case basis,” says Schmidt. “It will be up to the dealership to manage that. The primary recommendation is to not cover those (claims). But certainly there are things that can occur (that need to be considered).”

Other engine manufacturers are taking similar approaches on warranty claims caused by faulty DEF.

A key message engine manufacturers have been repeating for years is using non-certified fluids in your equipment to save a few bucks is false economy. Now, that includes DEF as well. “It’s just not worth the risk,” says Schmidt.

About the author


Scott Garvey

Scott Garvey is a freelance writer and video producer. He is also the former machinery editor at Grainews.



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