Starting with 2010 models, all diesel-powered vehicles in the U.S. feature a DEF system (diesel exhaust fluid). The purpose of the DEF is to reduce NOx emissions utilizing a management-controlled mist injection of DEF into the exhaust stream. DEF is a mixture of purified urea and purified water (refer to the May/June 2013 issue of Auto Service Professional for details regarding DEF systems).
Contaminated or improper-mix DEF can cause operational problems in these systems. In order to verify the purity of a customer’s DEF supply, a simple method involves the use of a refractometer.
While this type of tool has been used for decades for testing engine coolant, OTC now offers a refractometer specifically designed for the testing of DEF, available under part number 5025.
OTC’s 5025 DEF Refractometer is a portable, precision optical instrument designed to measure DEF concentration.
When a liquid sample is placed on the tool’s prism, the light passing through the sample is bent (refraction). The more concentrated the liquid, the more the light will bend. The refractometer features a reticle scale that is viewed by looking into the magnified eyepiece.
With no liquid on the prism, the eyepiece view will reveal a light blue background with the graduated scale. The background is an even shade of blue from top to bottom.
Once a drop of sample liquid is placed on the prism, a darker “shadow” will appear at the top of the scale.
The point at which the bottom edge of the shadow hits the scale indicates the condition of the DEF sample.
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