Can You Use Water Instead of DEF Fluid?

DEF fluid is a vital part of diesel-powered engines, and it’s important to make sure you have enough on hand. But what happens if you run out? Can you use water instead? 

You can use water instead of DEF fluid in a pinch, but it’s not recommended. The water will cause corrosion and ruin the SCR catalyst, which is an expensive fix. If you use water, be sure to flush the system with DEF as soon as possible. 

This article will go over some of the things you need to know about DEF and if you can use tap water as a replacement in an emergency. 

What Happens if You Use Water Instead of DEF Fluid?

You can use water as a temporary replacement for DEF fluid. However, this is not recommended as it can lead to expensive repairs. Some dealers will even recommend a complete DEF system replacement if water has been used. 

The reason why water is not a good substitute is that it can cause corrosion in the system. This is because DEF fluid is slightly acidic, and water is neutral. When the two mix, it creates an environment conducive to corrosion. 

If you use water, be sure to flush the system out with DEF as soon as possible. This will help to prevent any long-term damage to your vehicle. 

What Is DEF Fluid, and Why Is It Important in Diesel Engines?

DEF fluid is short for Diesel Exhaust Fluid, and it’s a crucial part of the emissions system in diesel engines. The fluid is injected into the exhaust stream, where it reacts with the NOx emissions from the engine to reduce pollution. 

This addition came as a response to stringent emissions standards that were put in place in the early 2000s. Before DEF, diesel engines were much dirtier and emitted far more pollutants. 

It is also worth noting that AdBlue systems do not affect the engine’s performance or the fuel economy. In fact, most engines will run better with DEF because it helps to reduce exhaust temperatures. 

If you run out of DEF fluid, your engine will go into “limp mode.” This means that the motor will be restricted to lower power output to prevent it from damaging the emissions system. 

Some manufacturers also limit the range you can drive in limp mode before the engine shuts off completely. This is to prevent damage to the catalyst, which can be very expensive to replace. 

How Much Does DEF Fluid Cost?

DEF fluid is not very expensive, and a gallon (3.8 L) usually costs around $6 to $10. This may seem like a lot, but you only use a small amount of DEF per mile. Consumption is usually less than 2% of the diesel used per mile (1.6 km). 

This means that a gallon of DEF will last you quite a while. For example, if you have a 20-gallon (76 L) tank, it will take approximately 1,000 miles (1,609 km) to use up the entire thing. That means most people will only need to fill up their DEF once or twice a month. 

Can I Make My Own DEF Fluid?

You cannot make your own DEF fluid. The recipe is a well-kept secret, and it’s impossible to replicate it at home. Car manufacturers have also made it difficult to tamper with the DEF system. 

If you try to use a different fluid, it will likely cause damage to your car. This is why I only recommend using liquids specifically designed for use in DEF systems. 

Still, some people suggest using distilled water as a temporary replacement. While this will not cause the same level of damage as tap water, it’s still not a good idea. 

How Can You Make Sure You Never Run Out of DEF Fluid?

The best way to avoid running out of DEF fluid is to check the level regularly. Most engines have a sensor that will tell you how much fluid is in the tank by displaying it on the dash. 

It’s particularly important to check the level before long trips, as running out of DEF can be very inconvenient. You may have to call a tow truck or wait for a dealer to bring you a new jug of fluid. 

Another way to avoid running out of DEF is to sign up for a subscription service. This service will automatically ship you a new jug of DEF fluid at a specified interval. This is an excellent option for people who don’t want to worry about checking the level regularly. 

How Long Does DEF Fluid Last in EcoDiesel Systems?

DEF fluid lasts a long time in EcoDiesel systems. In fact, it’s possible to go months without needing to top off the tank. However, this all depends on how often you use your vehicle and how many miles you drive each day. 

If you only use your vehicle for short trips, you may be able to go even longer without needing to add more fluid. That’s because the system will not use as much DEF when it’s not under load. 

It’s also important to note that the system will only use DEF when the engine is running. You won’t use any of it when your vehicle is parked. 

So, if you’re planning to store your vehicle for an extended period, you don’t need to worry about the DEF fluid going bad. It will last many months, and you can top off the tank when you’re ready to start driving again. 

Will DEF Fluid Freeze?

DEF fluid will not freeze in most conditions because it’s designed to work in low temperatures. The freezing point of DEF is 12°F (-11°C), so it can handle most winter weather without any problem. However, the fluid can freeze if exposed to frigid temperatures for an extended period. 

This is why it’s essential to keep your DEF tank full during the winter. If the fluid level gets too low, the tank could get cold enough to cause the fluid to freeze. 

You should also avoid storing your vehicle in a garage or shed that gets very cold at night. This can cause the DEF fluid to freeze, even if the tank is full. 

If you live in an area with icy winters, investing in a DEF heater is a good idea. This will keep the fluid warm, even when the temperature outside is below freezing. 

What Brand of DEF Fluid Should I Use?

You should always use a high-quality fluid that meets the standards set by the EPA. Some fluids are not as pure as they should be, which can cause problems with your vehicle. It’s also important to make sure that the fluid you use is fresh. 

I have used BlueDEF fluid (available on in my EcoDiesel truck for over two years, and I’ve never had any problems. This is a high-quality fluid that meets all of the EPA standards. You can order a two-pack, and it’s very affordable. 

Some gas stations also sell DEF fluid, but it’s often overpriced. It’s also not always easy to find a gas station that sells it. This is why I recommend buying it from a retailer like Walmart. 

If you’re not sure what brand of DEF fluid to use, you can always ask your dealer for a recommendation. They should be able to point you in the right direction. 

Will DEF Fluid Damage Paint?

DEF fluid will damage paint if left on the vehicle’s exterior for an extended period of time. If you leave DEF on your car’s paint, it will turn white and dull the paint. This is why it’s important to clean up any spills immediately.

You can use a soft cloth to wipe away the fluid or wash it off with soap and water. If the spill is large, you may need a pressure washer to remove all of the fluid. This should protect you from any damage to your paint job. 

However, DEF fluid is not corrosive, so it won’t eat through your paint or cause any long-term damage. It is just a small cosmetic issue that you need to clean up right away. 

Final Thoughts

I hope this article has answered your question of whether you use water instead of DEF fluid. As you can see, the answer is no. Water will not work in your diesel system, and it can cause damage to your engine. 

Always use a high-quality DEF fluid that meets the EPA standards. I recommend BlueDEF, but there are other good brands out there. You can also ask your dealer for a recommendation. 


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