Whats better for the Prius: Synthetic or Conventional?
If you plan to keep your car indefinitely like I do with my vehicles, I would use the best synthetic you can find as well as the best filters. I am an Amsoil synthetic lubricants dealer, so I have and still use Amsoil in all my vehicles. My '04 Prius has gone over 215,000 miles. Because I select the top-of-the-line Amsoil, I change the oil once a year or every 25,000 miles. I used a special by-pass filter and annual oil analysis on one of my cars and it went 170,000 miles and 9 1/2 years without an oil change. (There would probably be not enough room to mount a by-pass filter in my 2018 Prius Prime.) Be aware, not all synthetic oil is the same. In fact, there isn't even an industry standard to define true synthetic oil. If you are going to sell or trade-in your car in 5 or 6 years, use the free dealership provided oil. I do my own maintenance and have saved hundreds of dollars over the years. Toyota really makes great, long life vehicles but when it comes to oil and filters, the manufacturer's recommended products are not the best available. Good luck with whatever you choose.
Independent Amsoil synthetic lubricants dealer
2004 Prius 2nd Gen 115,000+ miles
2009 Tacoma 4W4 V6
2015 KYMCO Like 200i scooter
2018 Prius Prime Advanced