New to these forums,but I am a gm tech. DEF is injected into a chamber by the drive shaft. Not sure how that would ever harm the engine. Have not bought any from a truck stop for my duramax but wouldn't be afraid to.
The first nine months I owned my truck I only used Walmart DEF. Then 1 year ago the truck stop near my home put in a DEF pump at the diesel island. It may be my imagination or perhaps new truck break in period but I think I am getting better mileage out of the truck stop stuff vs Walmart.
For what it's worth...
Ken
2014 Ram 3500 diesel SB Crew cab
2014 Silverback 31RK
It is your imagination, DEF is DEF. It only effects emissions. It's quality is regulated like gasoline. You want to get DEF at the best price so you can do more camping.
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William & Sara
2012 Silverado 2500 HD DA
2014 Cedar Creek 38CK