Selective Catalytic Reduction (SCR) exhaust systems are the latest technology to improve fuel economy and lower emissions on heavy duty diesel engines. SCR systems rely on Diesel Exhaust Fluid (DEF) to allow engines to run a leaner air-to-fuel ratio, using less fuel and ensuring full combustion within the engine. DEF injected via the SCR system turns potentially harmful NOx into harmless water and nitrogen.
As fuel becomes more expensive and exhaust concerns continue to grow, keeping on top of your DEF tank means a significant savings. You use less fuel and harmful engine deposits are reduced because of full combustion.
However, when that DEF starts to break down, which happens with any chemical compound over time, it can be potentially hazardous to your truck’s engine. DEF with a urea content too low can impact your injection systems, triggering dash lights (we’ll address diagnostics in a later post) and engine de-rating. The result is less power and time off the road to figure out the problem, if you catch it soon enough.
To keep your truck running as intended, gauging the correct concentration of urea content in the DEF is your first step in ensuring the overall exhaust treatment system works properly. All manufacturers systems are calibrated to use DEF with mixed to 32.5% high purity urea and 67.5% deionized water. If you add DEF yourself, you have several options to test it while on the road or in the shop:
- Float type gauges – Least accurate and most difficult to read
- Manual refractometers – User reads the concentration off of a line graduations
- Electronic refractometers – Electronic measuring device with a digital display, giving you a precise readout of DEF contents
If you don’t fill yourself, make sure the shop you visit regularly checks their DEF for proper mix, and turns over their supply frequently. Like most vehicle fluids, the fresher the better, as evaporation and breakdown over time can cause your DEF to be out of specification.
A few questions could save you a few hours or hundreds of dollars down the road.