I have always purchased BleDef brand and never an issue. Looking at the reviews on the Walmart site I see what I consider to be too many one star reviews where using the Super Tech caused the DEF system to go into trouble and require expensive service.

Click here for reviews

I just bought my first diesel back in June. DEF is nothing but 32.5% urea and 67.5% deionized water. It turns into ammonia and will go "bad" over time. There is a manufacture date code on the Blue DEF. There is a chart out on the internet that breaks it down, don't know why they have to make it complicated. I never could find one on the Super Tech brand. My first DEF fill was at a major truckstop (around 3000 miles). The way I look at it, they aren't going to sell DEF that's bad to lots of trucks, and have to pay for all those repairs. The stocker at the big box store don't care about date codes and push the old to the back and put the new in the front. I would probably be the one to get the old one that had been on the shelf for a year. Like I said I am new to these new diesels also, looking forward to what others have to say.

I have purchased DEF at a truck stop, blue def, DEF at a local Exxon, and a jug of DEF from the ford dealership. Never had problems with any of them. It is cheaper to purchase at the truck stop or local gas station if you can find it.

Thanks to all for the comments.
What I'm learning is: (1) either purchase DEF in a container that has a date code on it (in a store/fuel station), or,(2) pump it at a truck stop where they pump/sell high volume so it is fresh?
So the only quality difference is in the age of the DEF, not in the chemicals that make it up, correct?
If anyone else has something to add, I'm sure we all will appreciate it.

Temperature has an effect on DEF shelf life - https://www.cumminsfiltration.com/sites/default/files/MB10033.pdf

"The shelf life of DEF is a function of ambient storage temperature. DEF will degrade over time
depending on temperature and exposure to sun light. Expectations for shelf life as defined by ISO Spec
22241-3 are the minimum expectations for shelf life when stored at constant temperatures. If stored
between 10 and 90 deg F, shelf life will easily be one year. If the maximum temperature does not exceed
approximately 75 deg F for an extended period of time, the shelf life will be two years. "

We purchased our 6.7 Ford in 2015. 2017 we were in Colorado and bought some diesel and someone had put def in it by mistake. I questioned myself for weeks about it. Had it in shop 4 times till they fixed it to where it ran like it should. Ford said then pull everything and replace $10000 to do it too. This was April 27th. In August we finally needed to get oil changed again. Took it to the local Ford in Delta, Co. and after we left Ford I noticed the fuel pump starting to make the same noise it had in Denver back in April. We in a few seconds the eng. went into low fuel pressure and reduced eng.npower mode. It would run 5 mph up a hill. I could type another hr. but to make a story short heres the final outcome. $9700 later and mind yall August till Oct. we finally had the complete fuel system replaced. It looks funny and concerning when you walk in and see your cab 8 ft. in the air and your eng. laying everywhere. The complete fuel system was replaced and fuel lines. only thing not necessary to replace was the fuel tank. The service manager told me to call my ins. people and they paid it off my comprehensive. Boy was that a break.
Now back to def. Since this all took place I get a signal to add DEF I find the next Walmart and by the cheapest thing available. Since then we have been to Alaska and back and all on the cheaper brand. No problems. Now mind you we full time in our truck. Its our main source of power and rider. Our truck as its known Fatbaby has performed as we have wanted.

Def is nothing special as far as one brand being superior to another. The cheap Walmart brand works just as good as the higher cost stuff. As Ray said it’s all about the age and what temperature it was stored at. So I buy my def based of what goes off the shelf fastest, and here they have a hard time keeping the Walmart stuff in stock so that is what I use. With my 2019 F350 6.7 diesel once the def gauge is at about 1/4 I put in 2 of the 2.5 gallon jugs and it fills it back up and I am good for about 4,000 to 5,000 miles of driving. I have heard stories of dealers accidentally putting def in the diesel tank so I will never have to hem top it off for me. If you ever accidental put def in the fuel tank do not start the truck and have it towed to the closest dealer. If you start it you are looking at a complete fuel system like Rush mentioned.

I just purchased a DEF tester and test the bottle before I put it the tank. That way you know you have fresh DEF.
ST

I didn't even know they made them for consumers. I will order one up. Thanks!

Yes, the DEF testers really give you piece of mind to know that the fluid you are using is acceptable.

I didn't know they made the testers either, how does one go about testing the fluid at the pumps?

Not sure it's as big an issue getting old DEF at the pumps but I would carry a small bottle to put some in and test before pumping in my tank. If it test good dump in tank and proceed to fill tank.
I will be trying that out here soon since I noticed the station near me sells DEF for $1.00 / gal.
Much cheaper then Walmart.
ST

I was an executive of Cummins for 15 years. Left Cummins to work for two global companies at a senior executive level. I’m very familiar with DEF, it’s development (in the North America market, it had been used in Europe long before) and its limitations.

I would highly encourage you purchase DEF from a bulk tank in a truck source. Age, storage, heat and cold can affect DEF. product

I have used both BlueDEF and Super Tech with good results. I always carry a jug just in case. I usually stick with BlueDEF even though it cost more. Since I usually need DEF every 2,000 to 3,000 miles while towing the cost difference per mile is negligible.

Wade, what are your thoughts on these consumer testers. Are they accurate enough for peace of mind?

https://www.amazon.com/Refractometer-Measuring-Exhaust-Concentration-Engines/dp/B07DLDZBS8/ref=sr_1_1?keywords=def+tester&qid=1569802934&s=automotive&sr=1-1-catcorr

Yes. I don’t think they are necessary if you make attempts to source from a high turnover inventory.

When I was doing research on DEF, I read where some people were getting DEF jugs from the trash or refilling the jug with just water and taking them back to the store for a refund. The poster suggested cutting a hole in the jug when empty.

Crazy stuff this DEF discussion.
I try to get mine at the truck stops (truck fuel lanes) as I figure it's fairly fresh because the supply is turned over often.
I hate the crusty residue it leaves when I spill it from a jug trying to balance the thing and keep the nozzle in the hole.
But that's just me.