Our Chevrolet Silverado 1500 ZR2 Duramax Uses a Lot of Diesel Exhaust Fluid. Is This Normal?
Saving the earth one plastic tote and cardboard box at a time.
Diesel exhaust fluid (DEF) is nothing new. GM’s Duramax-powered Chevrolet Silverado and GMC Sierra 2500HD and 3500HD pickups have had used the stuff since 2011. So has Ford’s F-Series Super Duty. While most manufacturers began their ramp-up early, the fluid didn’t become mandatory until 2015. Since then, all new diesel-powered pickups, SUVs, and cars have come fit with a selective catalytic reduction (SCR) exhaust system, and our long-term 2024 Chevrolet Silverado 1500 ZR2 is no exception.
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Selective catalytic reduction uses ammonia to break down NOx emissions into harmless nitrogen and water. It does this by first routing exhaust gases through an oxidation catalyst, which removes hydrocarbons and converts a small amount of NOx to NO2. The next step requires an injection of an aqueous urea solution—DEF—into the exhaust stream, which is then converted to the ammonia needed for the SCR catalyst to make its final nitrogen and water conversion.
The main benefit of a diesel SCR system for the vehicle owner is the potential cost savings the technology provides. Because SCR deals with harmful NOx emissions outside of the engine, manufacturers can tune them to both operate more efficiently and produce more power. Additionally, letting the engine run higher combustion temperatures results in a reduction of particulate matter and less frequent regeneration of the diesel particulate filter.
That all said, the fuel savings does come at the cost of the consumable diesel exhaust fluid. DEF is a mixture of synthetic automotive-grade urea and deionized water. It is clear, nontoxic, nonflammable, non-explosive, and generally nonhazardous. The fluid is mixed at a ratio of 32.5 percent urea and 67.5 percent deionized water.
Because the fluid is consumed during the system’s normal operation, it requires the owner to not only monitor the fluids level but also refill it when it’s been used up. Currently, a 2.5-gallon tote of DEF sells for between $15 and $25 at the local parts store.
Our Duramax-Powered ZR2 Is Quite Consumptive
Flipping through the Silverado owner’s manual, you’ll find a section dedicated to the diesel exhaust system. This includes helpful tips such as the expected refill interval of the exhaust fluid reservoir. Because there are a multitude of variables that affect exhaust fluid range, Chevrolet leaves it purposefully vague when describing how long the truck will go between fills, only stating that it should go “several thousand miles” between fill-ups. As the owner’s manual also says, “The amount of DEF used varies depending on driving style, trailer weight, loaded vehicle weight, weather, idle time, and other conditions.” In other words, your DEF usage will vary just like your fuel economy does.
Our first DEF refill happened at 3,276 miles, which consisted of mainly highway commuting, a 700-mile road trip, and one towing outing. The second fill occurred 2,978 miles later with the range dropping due to driving in heavy winds, some hard off-roading, and more towing. The best DEF range came to us right after our first scheduled oil change, and although it also included a fair bit of high-wind and off-road driving, there was no towing involved. Even though we only added 2.5 gallons at this fill, the truck was on track to go 4,680 miles or more than 900 miles per gallon of DEF.
