DEF

[Dlleno]

I've seen some posts here on the topic of DEF, and since I just finished doing some research on this topic and experimenting with my own truck I thought I would share what I have learned in the past year. apologies in advance for repeating others' thunder without proper credit.

* the storage requirement for DEF is entirely dependent on it's well-understood evaporation behavior. As fluid evaporates, the urea concentration rises and the sensors in your truck detect this and sound off. "Bad DEF" is really "Urea concentration out of spec". I'm not saying real contamination doesn't happen I'm saying 'contaminated DEF' is likely a misnomer - the fluid has just exceeded the urea concentration spec due to evaporation. no, there is no (inexpensive) way to restore the proper urea concentration of expired fluid, although doing so is physically possible (just risky and not worth the effort)

* the industry and the EPA have settled on a very precise urea concentration for exhaust dosing. thats why old fluid is not good -- it won't perform as EPA expects.

* the shelf life is well understood and dependent on temperature.

* if you are consuming DEF at a good clip (refilling every 3-6 months or less even in hot weather in most of the U.S.) then imho it doesn't make a dimes worth of difference if you completely fill or partially fill. Evaporation behavior depends on surface area, not gallons, so empty or full it won't matter.

* the important gotcha occurs when you are not driving regularly and the truck sits in hot weather. the shelf life gets real short real fast in very hot weather (like Death Valley, CA). in this case partial fills are the answer: I have been known to fill with as little as one gallon -- I put the rest of the "box" inside the house at 72 degrees where it will keep for 2 years. I use it after running the tank nearly empty

* no, there is no risk in running the tank down, which you should do every time. this is because every time you fill you are mixing old and new fluid, and you want your total to be as "new" as possible. If you are not driving regularly, and the weather is hot, run her down as far as you are comfortable, and fill with as little as possible to clear the warnings.

* there is much margin in the gauge and warning system, which was probably designed by lawyers instead of engineers :-). I routinely run my truck down to below "50 miles left before limp mode". just for grins I ran her down to 2 miles left -- one gallon of fluid cleared all the warnings

* avoid buying DEF in death valley, CA :-) where the average temperature severely limits DEF shelf life!

my truck is a Ram -- other's may behalf differently but its quite comforting to know where the limits are and how one can take advantage of them.

[egwilly]

Interesting information about the DEF issues....thanks for your research.

I had to have the def tank in my 2014 Superduty replaced under warranty 2 years ago due to the flapper valve inside the fill tube froze up and wouldn't allow me to refill the tank. It would literally take 45 minutes to slowly trickle one gallon of fluid into the tank. Ridiculous! If I tried just dumping in with the Ford approved hose, it would backwash and splash all over. Messy!

Once the DEF dries, it becomes a messy solid mass of crystals. Not the most friendly fluid for lines and DEF injectors.

Our tow vehicle sits most of the time since we don't use it on a daily basis. Mostly for towing the fifth wheel.

I have thought about drilling a hole in the bottom of the tank and fitting a drain plug in there so I can drain and refill with fresh chemical. Probably would void my existing extended warranty though.

[tuffr2]

Thanks for the post with all your findings. I few years ago I let a truck sit in the shade but in central Florida for 3 months. I was worried about the diesel fuel when I should have been worried about the DEF going bad. But as it turns out 3 months was ok. Neither went bad. Now longer than 3 months all bets are off to what problems I might have had.

But again, thanks for posting.[emoji106]

[Dutch Star Don]

I think DEF is more durable than it's made out to be, especially when it comes to heat. There is a lot of discussion about storage temps, but both Freightliner and Spartan, mount their DEF tanks within a foot of the engine and just above the exhaust system, with little insulation between them. So the DEF is constantly subjected to 180 - 200+ degrees every tie the engine is running.

You RARELY hear about a failure of the DEF system because of the actual DEF itself. It's typically a mechanical failure.

[Rollin101]

Originally Posted by Dutch Star Don

I think DEF is more durable than it's made out to be, especially when it comes to heat. There is a lot of discussion about storage temps, but both Freightliner and Spartan, mount their DEF tanks within a foot of the engine and just above the exhaust system, with little insulation between them. So the DEF is constantly subjected to 180 - 200+ degrees every tie the engine is running.

You RARELY hear about a failure of the DEF system because of the actual DEF itself. It's typically a mechanical failure.

I agree and I’ve let my Mh set for 6-8 months in Fl. with no ill effects on the def. How can it evaporate when it’s a closed system. My new Ram pickup says fill it with def every 10,000 miles with no mention of time.

[Dlleno]

The problem with heat is well understood, and the shelf life at any arbitrary average temp is easy to predict. The reason that the big boys don't care is not because they keep it cool its because their turnover rate is so high it just doesn't matter.

Evaporation occurs even though the tank is "closed". Its closed but not hermetically sealed. but again the risk only occurs when all of the following occur at the same time:

1. you get an old batch that has already evaporated some. so its 2-year shelf life (at room temp) is now only 1

2. you fill your DEF tank full

3. you're in very hot weather (I mean AVERAGE temps of Death Valley caliber) and don't use up the DEF within 3-ish months

The bottom line which I didn't stress is that if you buy fresh fluid and use it there is no problem. If you buy old fluid, park for three months in Death Valley, then you're in trouble. But not many of us do that :-)

Its really all about evaporation, which is well modeled and very well documented and understood. Again, the key is fresh fluid. I filled up my tank at a Love's truck stop last week, from the blue pump, and now I'm not driving my truck very much even though we are heading into the hottest part of our local summer weather. So my tank is full and my truck sits in a hot insulated garage. But i'm not worried -- the stuff will last longer than the hot weather will. unless of course you live in Death Valley

[IC2]

The life of DEF doesn't worry me. It will not evaporate in the jug and I really doubt that it will even in a vehicle's tank since that seems to be well sealed. I do not use DEF that is over a year old and will flush it down the sewer (it IS pee and water for all intents). I do keep a fresh jug in the S&B's basement though have successfully used DEF that was stored in the 5er's basement in Nevada. I do not trust the dash indicator on my 10 year od truck but will refil when it says less then 1/2 full though it usually is not. There is nothing mysterious about this fluid. Check the manufacture date and if storing some, keep it as cool as possible. If you are concerned about what's in the vehicle tank, you might be able to siphon most of it out and dump then install new

[NevadaNick]

I think the biggest worry about degradation of the def is sunlight. I will not buy jugs that are displayed in the window at a retailer. Well over a 1/2 million miles since 2011 with dsl vehicles that require def and not once did i ever have bad def.

[drdit92]

I've stopped buying it in jugs and just refill at the pump. It's much cheaper and no worries about what's in a jug (like the case of Walmart having people return them with just water inside and restocking them) or how old a jug is getting.

[chiefneon]

Howdy!

Thanks for the information. Do to the Coronavirus and insurrection occurring throughout the country we are not traveling much as fulltimers. That means the TV doesn’t get driven much. I can even remember the last time I added DEF to my truck much less diesel fuel.

“Happy Trails”
Chiefneon