in summer, our low is like 60~80 (we have had a low of 90 though!!!!!!) and our high as much as 120 (although mostly 115), should I run 20W-50 or 15W-40? Today was our first break of 100 for the year (and came two weeks later than last year, global warming... haha... haha...), it was 101 and I'm thinking It would be best to get a thicker oil soon.