I use Mobil 1 in gas, Rotella T in diesels. I read an arcticle that said synthetic oils aren't worth the money. However, that said, the US Govamint in their Stoopid ways is changing the formula for all motor oil starting in 2019 I believe. Double the price for everyone.
When you burn DEF you are burning Urea. Urea turns to amonia when heated. Amonia chrystalizes when it enters the lungs and mixes with moisture. When you can no longer breathe, blame the US Govamint. Just think, all the pickup and MH diesel spewing exhaust right into your AC vent.