Was debating switching my son's 2015 Accord over to full synthetic since his maintenance warning is light is set to 10k and he seems to have trouble remembering to tell me when he's coming up on his 5k oil changes (college students!). Have been using Castrol 5w-20 High Mileage and Fram in both his and my 06 Pilot at 5k intervals. Then I started wondering if fully synthetic might also be Ok for my 06 Pilot (but will stick with oil changes every 5k)? Think he's only at 120K and I'm at 180k miles. Costco has their full synthetic for about $12.50/5qts. as opposed to $27/5qts for Castrol synthetic. Not finding any bad reviews on Kirklands brand but it's also not showing in the top 5 or 10 when comparisons are being made. So two questions... 1) what's your opinion of Kirklands synthetic oil and, 2) should both vehicles be switched over? Would appreciate your opinions.