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Sweeper engines have gone through some big changes in the last ten years. And each change has brought additional costs, unfamiliar technology, and new maintenance requirements. One of those changes is the development of Tier 4 Final engines that require diesel exhaust fluid (DEF).

What is Diesel Exhaust Fluid (DEF)?

Diesel Exhaust Fluid is injected into the exhaust stream of the Tier 4 Final engine and this clear, colorless liquid in the presence of catalysts, turns smog-inducing Nitrogen Oxides (NOx) into harmless oxygen, water, and nitrogen.

DEF is stored in a separate stand-alone tank, usually located right beside the diesel tank. It commonly has a blue cap or another blue indicator to identify it as DEF (whereas diesel is often associated with the color green).

How much DEF does a sweeper consume?

As a rule of thumb, sweepers will consume an amount of DEF equal to roughly 2 to 10 percent of the fuel they burn. How much DEF your Tier 4 Final engine consumes depends primarily on who makes the engine. Emissions reduction in Tier 4 Final engines is a balance between selective catalytic reduction (SCR) which uses DEF, and exhaust gas recirculation (EGR). The more DEF an engine uses, the less EGR it needs. The more EGR, the less DEF.

How often do you refill the DEF tank?

Most engine manufacturers have sized their DEF tanks so that you refill the DEF every time, or every other time, you refuel with diesel. That makes it easier to remember, and less likely that you or your technician will forget.

What happens if a sweeper runs out of DEF?

Unless you or one of your technicians is negligent, you shouldn’t run out of DEF. Sweepers with a Tier 4 Final engine will have a gauge or indicator on the dashboard or console to tell you how much is in the tank. If you do run out, the engine will either shut down or derate to the point where you can’t work.

DEF tanks have only sediment filters and lack the kind of high-efficiency filtration common to diesel fuel and air systems. You don’t want to handle DEF the way you handle fuel or lube oils. When refilling the DEF tank, you have to clean around the fill neck and the dispensing nozzle every time. And while DEF does not “harm” many materials, it is the metal of many storage containers (such as aluminum) that will leach into the DEF and contaminate it. DEF should never touch any metal except stainless steel.

Although it’s not difficult to manage a DEF component in your maintenance, it needs to be part of your discussion and consideration when buying equipment from your sweeper dealer. That conversation doesn’t have to be long, but everybody who will work with or will work on the sweeper needs to be educated to prevent problems.

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