I have a 2004 Toyota Rav 4. It's at about 185000 miles and due for an oil change. It's always had 10 w30 conventional oil. I used to get oil change at dealer and interval was every 5000 miles. Recently (last year or 2) I have been going to quick oil change places and it has been 3000 mile interval. I am considering changing to synthetic oil (maybe even doing the changes myself?) to get a few more miles between changes. Is it OK to use synthetic oil in this Rav4? Are there any caveats or other things I should consider before making the decision? Thanks so much!!!