1st We manufacture DEF under contract.....Their are no laws to stop anyone form producing it. If you want API cert DEF and want to Pay Blood money that's your choice. Many BIG freight companies produce their own or purchase it form producers, that are NON-API cert.
The correct concentration 67.5 DW and 32.5 Urea bring the freeze point down to 12-14F. This concentration level has very little expansion at it freeze point.
During the summer months I use Deionized water only , when fall arrives I switch back to 60-40% or so.
DEF Evap is a NON- issue I stored Gallons of DEF for 3-5 Years at the Shop and
Just curious if you measure the 67.5% water /32.5% urea by weight % or by volume%??????
If you measure them by volume and change that same quantity to weight percent, then you have 61% water and 39% urea. So your mix could be anywhere between 60/40 and 70/30. This is not a huge swing, but if you are starting with the wrong percentage, and the stock changes relative to temperature/humidity/exposure, someone you are advising could have trouble.
Additionally, if you are using technical grade urea, instead of reagent grade urea, then you can likely get some sodium, chlorine, iron and other minerals in the stock that you are mixing. If you are using urea used for cleaning, i would not chance buying your homemade DEF.
I will continue to buy my ISO certified urea, because i don't know if they report percents by weight percent or volume percent. But they do follow a standard.
I will continue to make my own judgements about how much DI I add. A (former Ram/Cummins) diesel tech on this site once said, "you can't hurt anything by using slightly diluted DEF, but you can clog or damage the system by using too concentrated of def."
Minnesota doesn't have as dry of air as arizona, new mexico, utah, etc. So i doubt that the water will evaporate out of the def as quickly in some states/regions as other states/regions. Also, there will likely be very little evaporation at colder temps as compared to drier temps.
I'm glad you have a business selling abd supplying DEF. But unless you explain exactly which stock you are using, how you store it, and the procedure by which you mix it, i would not try to save money there now that i know how expensive these emissions parts are.
https://www.equipmentworld.com/def-contamination-and-how-to-avoid-it/
https://www.cvacoop.com/Blog/March-2018-(1)/Diesel-Exhaust-Fluid-(DEF)-FAQ-s