Realizing that UOA's don't seem to show much difference. I am going to 30 wt. My 2016 Spark will hopefully last me the rest of my driving career (am 72). It gets 38 mpg in summer and 36 mpg in winter on 5 mile trips into town (75% of driving). Not a big deal. Certainly not worthy of discussion. I guess I have too much time on my hands..lol.