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March 06, 2014  |   Comments (0)   |   Post a comment

Web exclusive: Getting the most out of DEF

Understanding some basic facts about diesel exhaust fluid (DEF), such as its freezing point, the importance of using high-quality DEF and keeping it clean, and proper storage procedures, will go a long way in its efficiency in a selective catalytic reduction system.

by Mike Mavrigian


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Misco offers digital refractometers. The model 201 refractometer offers a single-scale readout.Photo courtesy of Misco
<p>Misco offers digital refractometers. The model 201 refractometer offers a single-scale readout.<br /><small>Photo courtesy of Misco</small></p>

Home-brew alternatives?

Just because the DEF solution comprises a mixture of urea and water, this does not mean that you can whip up your own batch. The urea used in DEF is a very high-purity synthetic, and it is not urine. Also, the water used in DEF must be extremely pure and deionized. The bottom line: No, you can’t make your own DEF by mixing urine and tap water. DEF is a sophisticated blend designed specifically for SCR systems.

Allowing impurities such as calcium, copper, magnesium, etc. (which would/could be present in urine and tap water), would introduce impurities that can kill active sites in the catalytic converter (the ammonia itself won’t harm the sites). Continued use will eventually make the converter inoperable, requiring converter replacement.

Also, do not add anything to the DEF tank except actual DEF. If someone, by accident or ignorance, dumps diesel fuel treatment/booster into the DEF tank, this will kill the entire SCR system, resulting in a repair bill of thousands of dollars. Pay attention. You wouldn’t add orange juice to your fuel tank or Pepsi to your cooling system, so don’t add anything but the correct fluid to the DEF tank.

Along the lines of DEF purity, consider the quality of the DEF. The major brands (Peak’s BlueDef, ACDelco, Motorcraft, etc.) offer the highest quality both in terms of purity and proper urea-to-water percentages. However, there are a few bargain-priced brands out there that feature a higher water content, which isn’t as efficient and won’t last as long as anticipated. In other words, stick with the major brands.

Keep it clean
Whenever handling DEF, the fluid must be kept clean. If a funnel is used, it must be absolutely clean and free of any contaminants. It’s best to dedicate a funnel (and label it) for DEF only. Spare DEF should be stored in its original container, with the lid/cap secured, to avoid airborne contaminants in the shop. Do not transfer DEF to another container that previously held anything else (oil, windshield wiper fluid, coolant, etc.). Avoid cross-contamination! It doesn’t take any extra time to handle DEF properly.

FYI: Urea is corrosive to metals such as copper and brass. DEF systems are typically plumbed with high density polyethylene.

Verifying DEF quality
All API (American Petroleum Institute) certified DEF will feature an API symbol on the container. Use only API certified DEF.

The concern with DEF quality (beyond API certification) is the potential for water dilution. Just as water can enter a fuel system, it is possible for water (moisture) to enter the SCR system and slightly dilute the DEF. One indication that the DEF has been diluted is when the vehicle uses more DEF than normal (beyond the mileage use specified by the vehicle maker).

An easy field test to check for the purity of DEF is with the use of a hand-held refractometer. A refractometer that is designed for testing DEF will easily allow you to verify the water content.

A refractometer is a precision optical instrument designed to measure the concentration or mixture of water-soluble fluids. It measures refractive index, which is the speed at which light passes through a liquid. The more dense the liquid, the slower light will travel through it, resulting in a higher reading.

Applying a few drops of the vehicle’s DEF to the refractometer is all that’s needed. DEF refractometers (those units capable of measuring urea concentration) are available with single scale or dual scale readouts. The single scale provides a percentage of urea by weight. A dual scale unit also provides a refractive index scale readout, which is primarily used by manufacturers and distributors of DEF (a quality control aid). For shop technicians who simply want to check for water dilution, a single scale unit will suffice.

Citing two examples of DEF-capable refractometers, MISCO U.S. offers a digital single scale unit (its DEF-201) that retails for around $350. The reading will provide a precise level of water content to +/– 0.1%. The dual scale unit (DEF-202) retails for around $435. Either model is powered by a pair of AA batteries.

OTC (Bosch Automotive Service Solutions) has released the OTC-5025 DEF refractometer, which retails for around $114. The kit includes a refractometer, dropper, lens wipe cloth, instructions, screwdriver and storage case. The refractometer features a reticle (scale) that is enlarged through an eyepiece to measure light. The values on the scale have been established to specifically evaluate DEF condition. OTC’s unit features 0.5% line graduations, with a scale range of 15% to 40%.

Regardless of the brand you choose, a DEF-capable refractometer is a useful and must-have checking tool for any shop that services diesel-powered vehicles. This eliminates guesswork with regard to the quality (in terms of water dilution) of customer DEF tank contents.

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