Putting diesel exhaust fluid (DEF) in a diesel fuel tank can lead to significant repair costs if it is not handled correctly. If you identify it early and take the right precautions, you can correct the situation with little damage.
If it goes untreated, or if you start the engine, you could end up with complete fuel system contamination, injector corrosion and diesel particulate filter (DPF) issues. DEF is not fuel — and because it is mostly water and urea, it lacks lubricity and can cause serious damage to diesel fuel system components. If it ends up in your fuel tank, you need to take immediate action. Learn more about using DEF and review the expert-recommended steps to prevent catastrophic engine damage in the event that you have DEF in your diesel fuel tank.
What Is DEF?
DEF is a urea-based solution used for selective catalytic reduction (SCR) systems. DEF is approximately 32.5% urea and 67.5% deionized water, making it ideal for SCR systems but harmful if introduced into a diesel fuel system. While it has significant benefits when used as intended, misused DEF can cause complete diesel fuel system damage and contamination.
Why Putting DEF in the Fuel Tank Is Dangerous
What happens if you put DEF in diesel? Since DEF is a urea‑based, water‑rich solution, it contaminates diesel fuel and disrupts the lubrication and operation of fuel system components. When it gets into your diesel tank, then into your diesel system, it can cause catastrophic corrosion to fuel injectors, pumps and oil lines, as well as potential performance issues and long-term engine damage.
If you turn the engine on before treating the issue properly, DEF can cause immediate damage to your diesel tank.
Signs DEF Has Contaminated Your Diesel Fuel
There are a few signs that DEF has contaminated your diesel fuel, including:
- An engine that won’t start
- Internal warning lights and error codes
- Noticeably strange or strong fuel smoke and smells
Immediate Actions to Take
If there’s DEF in your fuel tank, follow this advice to minimize damage.
Do Not Start the Engine
The most important thing to remember when DEF gets into your diesel tank is that you should not start the engine.
If you start the engine, DEF can be circulated throughout the fuel system, increasing the risk of widespread contamination and damage to injectors, pumps, and other components. The cleanup will cost hundreds if not thousands of dollars to fix.
Call a Tow Company Immediately
Once you have a good handle on the situation and you know the amount of DEF in your tank, call a tow company. At this stage, prioritize safety and wait for professionals to arrive.
Inform the Service Provider About Your Diesel Engine Contamination
When professionals arrive, detail the severity of the situation. Your local experts will know how serious the situation can be, but they need to know a few key things about your specific situation to provide the best service possible:
- How much DEF was added to the tank
- The level of diesel fuel already in the tank
- Whether the engine was started
- Any strange smells or sounds you noticed
Once professionals know about these key details, they can accurately and effectively perform a full tank flush and refuel, or assess any further severe damage that may have occurred.
Preventive Measures to Avoid Future Mistakes
Keep DEF-related accidents from happening with these tips.
Label Your Diesel and DEF Fill Points Clearly
Never underestimate the power of clear labels and colors. To avoid the same thing happening again in the future, make sure to label your diesel and DEF fill points clearly with alternate colors. Make sure that your storage containers for each individual DEF and diesel fuel canister are also labeled with the same color.
These practices can prevent confusion between the fill points in the future, avoiding costly damage to your diesel system.
Educate Drivers and Staff
If you are working with fleets, commercial trucks or RVs on a daily basis, more than your individual processes need to be monitored. It’s essential that you provide basic training on fuel types and DEF handling to any workers in your facility.
Double-Check Before Filling
Always double-check what you’re adding to your vehicle. The most important way to prevent future mishaps is to develop a habit of confirming that the nozzle and tank are correct before adding diesel or DEF into your system. Once it becomes second nature, you can effectively eliminate future DEF and diesel catastrophes.
When to Seek Expert Help
At Hot Shot’s Secret, we understand how DEF contamination affects diesel systems and why proper handling is critical to avoiding unnecessary damage
Prioritize safety and avoid DIY fixes, as improper handling can push DEF further into the fuel system and increase the risk of damage.
Use DEF Properly With Products From Hot Shot’s Secret
While DEF contamination in the fuel tank can cause serious problems, DEF plays a critical role in the emissions system of modern diesel engines when it is used exactly as intended. Hot Shot’s Secret Premium DEFender™ is formulated to address DEF crystal buildup and protect SCR system components. Ideal for all diesel engines equipped with an SCR system, Premium DEFender is compatible with all DEF brands and should be added during each refill.
Purchase your DEF additive today and complete your next refill with confidence.