I mean should I put it in the new van (2004 Sienna-3,200 miles) which only calls for 5w30 per the manual or the much older Trooper which can take pretty much heavier weight oil? This stuff is quite pricey. I paid $4.99 per quart at the local Autozone but I was so excited to see it that at first the cost did not really hit me until I got home I realized what I paid. Anyway just want to ask you guys: At which point (mileage-wise) should I switch the van to synthetic? Currently it's running dealer oil after the old Pennzoil was changed out. Will you use the Syntec 0W30 in Arizona temperatures? If not, what weight oil do you recommend? I'll be driving there this weekend. Thanks for your opinions.