DEF life span and quality considerations

[Neal]

A lot of chatter on the web of late regarding DEF. While I don't know the details or causes I have a concern on DEF quality based on how many maintain DEF in their RV's. A lot of people like to keep their DEF tanks full, some may let it go down one indicator value such as 1 dot out of 4. Camp Freightliner pushes the rule of thumb to let it go down to two dots (half tank) prior to filling. I'm nearing the end of a long trip and I recently let my DEF get a little lower than normal, intentionally. I wanted to go lower but chickened out.

The concern many have is crystallization of the area above your DEF level. My concern and the reason I let my DEF get down to 1/2 tank prior to filling is DEF concentration, or quality. DEF has a lifespan, it does not last forever, from what I understand. If the DEF is not completely cycled out of your tank then over time you are effectively diluting your DEF by adding new to old, constantly. DEF should effectively be at a 100% concentration, in layman's terms but if you are only adding a 1/2 tank of new to 1/2 tank of old each time, what is your net effective concentration?

If I could I would drain my DEF tank annually and fill with fresh DEF. I haven't looked at what it would take to do this but my concern is growing that over time we are just reducing the quality of DEF in our RV's. My understanding from FL is you can actually run out of DEF and still travel 1,000 miles to get to a location to get DEF. I don't want to be the one to test this nor have I heard of anyone that has but the point is the system is designed to let you completely run out and not immediately de-rate you. I need to work harder on letting my DEF level get lower so I can ensure a higher concentration of quality of DEF is in my system.

The other option is to TEST your DEF. I actually own a refractometer, it's in my pegboard bay, I have yet to use it. When I get back to storage I should test it and see what it reads. I invite others to test your DEF as well and reply with your findings and share your practice of DEF management as described above and let's see what kind of statistics on DEF quality we can come up with.

DEF Refractometer for Measuring Diesel Exhaust Fluid Concentration of Diesel Engines: Amazon.com: Industrial & Scientific

DEF Refractometer for Measuring Diesel Exhaust Fluid Concentration of Diesel Engines: Amazon.com: Industrial & Scientific

www.amazon.com

 

["EZ"]

Your concerns are valid Neal. If I owned a DEF using RV and only travelled 10k miles a year or less, I don't think I would ever fill my tank over half way so the DEF would be used and not just sit in the tank aging. Also the MOST IMPORTANT thing to remember about DEF is that HEAT is the killer. If your RV sits in the sun for months at a time in a storage lot or at a treeless campground your DEF has a life span that is measured in weeks, not years like it would be if it was stored inside a building at 75-80 degrees. Also do not buy any gallon jugs from a parts store with a display in the window with the sun beating in on the jugs all day!!! The heat will make the DEF go bad very quickly!!

My advice is to base how much DEF you put into your tank by how many miles you plan to drive this month. The least amount of DEF you put in the tank the better. This way you are always using FRESH DEF. Your exhaust sensors will thank you and so will your wallet.

 

[MapNerd]

What’s the average mpg for DEF? If you could figure that out, the one could easily determine how much DEF to add at each fuel stop. If you could keep your DEF refills in sync with fuel refills, that would make life easier I think.

 

[Neemer]

It’s frustrating how much divergent information is circulating on this topic. At FPU, my tech said to keep it at the 75% full level. At the latest AIM rally, a Freightliner rep said to keep it full. I’m going to begin keeping it as full as possible per the FL guy. We’ll see what happens with that.

 

[Joe Hogan]

DEF consumption will be approximately 2% of the diesel fuel consumed. Another way to consider it is that DEF will be consumed on a 50 to 1 ratio with diesel. (For every 50 gallons of diesel fuel burned, you will use 1 gallon of DEF).

Cummins Filtration | › ...
PDF

Diesel Exhaust Fluid (DEF) Q & A - Cummins Filtration |​

 

[Neal]

There are a lot of “techniques” and guidance out there, you have to use your own common sense and judgment, ultimately it’s yours, do as you want to do.

The same concept applies to people that don’t let their fuel tank run down, that’s octane or diesel. You’re mixing in fresh with old, constantly. This is why I try to let my diesel run down to 1/4 tank when refilling so I’m out with the old, in with the new, getting a fresh tank of diesel cycled. Same applies to your fresh water tank, let it drain, then refill, otherwise you’re carrying around aged water for a very long time.

 

[Joe Hogan]

Some additional information

Old World Industries Commercial and Industrial Chemical Sales, BlueDEF Americas #1 brand for Diesel Exhaust fluid products - Commercial - Old World Industries

OWI Commercial and Industrial Sales, Specialty Chemical Sales, with brands such as Final Charge, Full Force, Fleet Charge, PEAK, Thermal Charge and chemicals including, Caustic Soda.

www.peakhd.com

 

[FL-JOE]

It is hard to gauge you DEF usage IMHO because you will use more when towing a load compared to not towing a load. Of course this only applies to folks using diesel trucks pulling RVs, not motorhomes.

I have read about everything out there on DEF storage and usage since getting my first vehicle equipped with DEF (2012 F350). To be honest I think it is like fuel or gas. Modern gasoline doesn't stay good forever and you certainly don't run your family vehicle down to empty each and every time you fill up, so in reality you are mixing old with new constantly.

I put almost 50,000 miles on my previous F350 and I simply added DEF when it was half or just below half full. Never had any type of issue. Neil I think you are concerned about something that isn't a problem. Any crystals, and there will always be some inside the tank, will dissolve when liquid DEF contacts it.

 

["EZ"]

It’s frustrating how much divergent information is circulating on this topic. At FPU, my tech said to keep it at the 75% full level. At the latest AIM rally, a Freightliner rep said to keep it full. I’m going to begin keeping it as full as possible per the FL guy. We’ll see what happens with that.

Here's a quote from the article Joe posted that Peak brand DEF wrote on the topic. It's exactly the same thing that I posted above. It's exactly why you don't want to keep your DEF tank full, ESPECIALY in the Summer heat. The Freightliner guys are trained to think about tractor trailers. You should always keep their tanks full because they are putting on tons of miles every month. Most RV's sit more than they drive so the DEF is just baking in the sun. BIG difference in the two applications.

• • The best temperature for storing DEF is 77°F. Higher temperatures will not affect the quality of the DEF, but will impact its shelf life. The quality of DEF also is not affected if the fluid freezes. When stored under optimal conditions — between 12°F and 86°F — DEF has a shelf life of up to two years. If stored in warmer temperatures, shelf life decreases.

Be smart. Don't store your DEF in the tank sitting outside in the heat. It will KILL the shelf life. Put what you have to in the tank and keep the rest stored in a cool dry place. OR better yet, just put a little DEF in every time you get fuel from the underground storage tank at the truck stop. Then you know it's fresh!

 

[Neemer]

Higher temperatures will not affect the quality of the DEF, but will impact its shelf life.

That statement appears contradictory to me. If shelf life is affected by high temps, then it must also affect quality. Unless quality falls off the edge of the table at the end of shelf life, there has to be a degradation curve. I’m not taking issue with you, EZ, but I’d like to see some real data on this. Two years is a long time. What exactly is the impact? Halved? Worse?