Our Chevrolet Silverado 1500 ZR2 Duramax Uses a Lot of Diesel Exhaust Fluid. Is This Normal?

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.

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.

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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.

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Towing Makes Things Worse

It’s not unexpected that putting a load behind the truck increased the rate of exhaust fluid use. What we weren’t prepared for, however, was just how much greater that usage would become. On long highway slogs with a trailer, we found the DEF tank ran dry in as few as 750 miles. Depending on terrain, speed, and wind with 8,000 pounds in tow, the Silverado averaged between 137.6 and 160.8 miles per gallon of exhaust fluid. With a 5.5-gallon DEF tank, that offered roughly 750 to 850 miles of range, requiring a refill after every other fuel stop.

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Fighting the False Information

The exhaust fluid usage rates weren’t entirely unexpected, but what the truck did when it thought it was getting low certainly was. Under normal conditions the driver information center displays a series of warnings beginning with “1,000 miles until empty.” The warnings get increasingly aggressive until the truck eventually limits the max speed to 65 mph. Drive 75 more miles, and speed is further limited to 55 mph, and after a final 75 miles of not refilling, the truck gets limited to a maximum speed of just 5 mph. These speed limitations are due to government regulations ensuring that the truck is not operated without the SCR system functioning.

There’s also a digital gauge that displays tank volume in increments of eight. However, the gauge does not operate as a simple meter of fluid level. Instead, Chevy has programed the system to respond dynamically to driver inputs and the current vehicle usage. For example, when driving at higher speeds, into stiff wind, or especially while towing a load, the truck’s computer will calculate the current rate of exhaust fluid usage based on that scenario and create an artificially larger buffer to prevent accidentally running dry.

This is all good in theory. In practice, however, it often created an enormous headache. Once the DEF system alerts that the tank is low and begins its 1,000-mile countdown, it locks out every other function of the DIC. There’s no way to cycle through the trip computers, tire pressure monitoring screen, off-road screens, or anything else. This leaves the driver with a low-DEF warning and just the most basic information. A minor annoyance, sure, but making matters worse is the fact that the tank was never actually low.

If the system reset, either once the condition that set the warning has passed or after a key cycle confirms that the fluid isn’t low, we’d be OK with this behavior. However, the fact that we’ve needed to fight this cycle every time we hitched a trailer to the truck has created a consistent pain point that should be easily remedied.

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How Consumptive Has It Really Been? 

Over 19,000 miles, we’ve averaged 2,714 miles per 5 gallons of exhaust fluid in mixed driving that has included more than 3,000 miles of heavy towing. However, that only tells part of the story. During this same period, we’ve added 35 gallons of exhaust fluid at a cost of $255.50. At first blush that might seem like a big number, but it equates to just about $0.015 per mile. That's worth the price of admission if it means more power, better efficiency, and cleaner air.

More on Our Long-Term 2024 Chevy Silverado 1500 ZR2 Duramax:

• Is This the General’s Best Off-Roader? Long-Term 2024 Silverado ZR2 Arrival
• We Broke In Our Yearlong Review Silverado ZR2 By Driving It to the Bottom of the Grand Canyon

• So Close to Perfection: 2024 Silverado ZR2 Interior Review  
• What We Learned Maxing Out Our Silverado ZR2’s Tow Rating
• It’s Going to Cost $300 Per Year to Keep Using Google Maps
• Our Silverado ZR2 Has 823 Miles of Range… No, Really.

• Sometimes Bigger Isn’t Better  
• Chevy’s Multi-Flex Tailgate: Is It Rad or a Total Scam?

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