I change mine once a year. I average about 8000 to 10,000 K miles per year. Some folks are driving 15000 and more! Hal
A longer oil change interval is the most compelling reason to use synthetic, the second being running 0W-20 if you live in an extremely cold climate. These engines wear just fine on regular oil, and there is questionable increase in fuel economy by running the lightest possible weight, which again is 0W-20 and is only available in synthetic. If you switch, be sure to monitor oil consumption, as that has been reported by a few users. You can go anywhere from 10,000 - 20,000 miles, depending on whether or not you do oil analysis.
Running 5W-30 synthetic in my Iconic Prius (2004) showed a small bump in efficiency. Combined that with a worry-free 7,500-mile change-interval, there's no reason not to switch. Whether or not the switch to 0W-20 makes a worthwhile difference in that model is uncertain. But it works great for the 2010 every 10,000 miles. .
Yes elfprofessor. Many parts of Europe even specify a 15,000km (9000 mile) oil change interval for the Gen2 Prius. I'm changing every 6 months at about 9000 miles and it's going just fine. For the longer drain intervals I recommend using an oil with an ACEA rating, A1/A5 if your in a cold climate or the slightly thicker A3/B3 for really warm climates (like here in Australia).
I started progressively extending my interval by 2500 miles with each change after the drive train warranty expired, but only with a used oil analysis each time. So far I'm up to 12,500, though that change was recently done and I haven 't yet sent the sample to be analyzed. I've been using Mobil 1 5W-30 since the second oil change.
My '04 Prius has about 122k trouble free miles thus far maintained on 5w-30 ACEA A1/A5 synthetic oil changes twice yearly. For the upcoming winter I will use 0w-20 to try and eke out a couple more percent improvement in fuel economy. 55 mpg in the winter would be very nice, 60 mpg is a holy grail. Currently low 50's for overall winter driving.
