DEF and the wide difference in price

[geotex1]

Now Im wondering what the shelf life of DEF is? Can you keep a half box in your garage over the winter until the next summer?

No. Don't keep half used DEF around. Fresh and sealed will be fine over a winter stored in the garage.

[Thorvald]

If you want to learn good bit about DEF, watch the two videos from Motorcity Mechanic. He includes a full video about how to test.

Part 1: Tech talk #8 Part 1/2: Everything you need to know about DEF fluid
https://youtu.be/Tvh7-KhGlzo

Part 2: Tech talk #8 Part 2/2: Everything you need to know about DEF fluid
https://youtu.be/yBGlx4XefrM

After watching a ton of silly videos on how to decode date codes on boxes, I’ll stick with the Mopar DEF for my new truck. It’s almost the same price as most of the others and I can’t justify saving a few dollars and risking bad or substituted DEF on a $100,000 truck!

At least Mopar puts the expiry date right on the jug in English and the dealer can never blame the quality of the DEF when I have the receipt and the jug showing it’s not expired.

Too many horror stories out there.

[MarioG9999]

I have not found any difference in mileage in different DEFs. I try to buy mine at large truck stops, e.g., Loves, Circle J, etc. Cost in Nevada is $3.00 a gallon. Pump very slowly as the wide houses will split back at you.

[huntindog]

Walmart brand $7.92 2 1/2 gallons always fresh check the seal/date. Would use truck stop when available.

This is what I do.
I would never use the pump DEF.
Truck stops are usually pig sties. The pumps often gross, including the DEF pumps. And you CAN get bad DEF at a truck stop. You have no way of knowing just how old or dirty the DEF coming out of the pump really is.... You are just trusting that it is OK.... Relying on some mimimum wage employee(s) that you never see to do their job right.

Using boxed DEF (WM has best price) I can make sure it is sealed and in code.
This is very important as any contaminents that find their way into the DEF tank can cause expensive/inconveinient problems.
Our trucks use so little DEF as to make the price differences immaterial