Wednesday, July 23, 2025

What’s DEF? | The Every day Drive


Somewhat DEF cleans a number of air.

Gasoline-pump facet DEF dispenser.

Generally known as DEF, diesel exhaust fluid is an emissions after therapy, launched to the exhaust fuel of a diesel engine to decreased nitrogen-oxide (NOx) emissions.

You might have seen DEF (also called AdBlue, which is a model title) within the aisles of a truck cease or ironmongery store. The fluid, which is comprised largely of urea and water, is usually offered in 1- and a couple of.5-gallon containers, in addition to bigger vessels to be used in over-the-road vans. DEF can be retailed at truck-stop gasoline pumps in bulk kind, which is handy for truck operators, as massive tractor trailers usually have DEF tanks as massive as 20 gallons. Diesel-powered pickup vans have smaller DEF tanks, sometimes 5-6 gallons.

What’s DEF?

Emissions

Essential to the operation of what’s often known as the Selective Catalytic Discount (SCR) system, DEF employed appropriately may also help to scale back NOx emissions by as a lot as 90 p.c. One of the crucial harmful byproducts of diesel combustion, NOx emissions contribute to respiratory issues, acid rain, and ground-level ozone, also called smog. Environmental Safety Company (EPA) rules mandating the usage of DEF have been handed into regulation in 2010, requiring that every one heavy-duty diesel engines constructed starting in 2015 make use of the SCR system.

Diesel Emissions Fluid in 1-gallon jug.
DEF in 1-gallon jug.

DEF Packaging and Costs

The fluid itself, which is about two thirds water and one third artificial urea, is just not particularly costly, and might run from $8-$12 per gallon, relying on the retailer and bundle measurement. The pump-side dispensers are typically the least-expensive buy possibility. A 20-gallon DEF tank will present a typical over-the-road truck with about 6000 miles of operation.

Limp Mannequin

By regulation, as soon as a automobile’s DEF discuss is depleted, the truck in query will function in “limp” mode, which reduces engine energy output till fluid is added to the tank. A warning that the DEF tank is approaching empty sometimes seems on a truck’s instrument panel roughly 100 miles upfront of full depletion.

Tampering

Whereas it was briefly well-liked for the operators of diesel-powered vans to take away the SCR methods, that motion has confirmed detrimental to long-term possession of the automobile. Not solely is tampering with the SCR system unlawful, many dealerships will decline to take an clearly tampered-with truck in commerce.

Autos

Truck requiring DEF use embody diesel-powered heady-duty variations of the Chevrolet Silverado, Ford F-Sequence pickup, GMC Sierra, and Ram pickup. These along with all diesel-powered medium- and heavy-duty vans.

DEF filler port.
Within the case of many pickups and medium-duty vans, the DEF filler port (blue cap) is positioned subsequent to the gasoline port.

Deal with with Care

Dried DEF tends to crystalize on automobile surfaces, so care ought to be exercised when including the fluid to your automobile. Left to dry, DEF might fade painted physique panels.

Diesel Emissions Fluid SCR System
DEF SCR system.

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