Our Prius just passed 100K miles and I am no longer covered by any warranty on the ICE. I have been regularly changing oil every 5K using Castrol oil & Toyota filters but am planning to switch to Mobil 1 and changing interval to 10K. I change my own oil and we put lots of miles (30-35K/yr) mostly long distance traveling. There have been some old wives tales about changing to synthetic oil on cars with a lot of miles. I assume that they are just that - old wives tales. I am fairly convinced by other posts here that going to 10K intervals is OK. Any thoughts about making the switch at 100K? What about weight of oil? Due to the milage, should I stick with 5W-30, or could I go with 0W-20 or 0W-30? I suppose I could try the 0W-20 and carefully monitor oil consumption, switching to 0W-30 then 5W-30 if consumption goes up. (Right now, consumption has been nil.)
Use Mobil 1 5-30 at 10K Intervals. Use the factory filter. I change the filter every 5K miles. Its cheap. You are really using that car alot. Keep after the trans fluid too. Its due. I change mine every 30K miles. Wait till you see what it looks like at 100K. And if your really handy its not a bad idea to pull the plugs and look at them before they get seized in the motor. When replacing use anti corrosion on the threads. Basic car stuff.
Well, I have two cautionary tales for you to consider or ignore, as you prefer: 1) My Ford Mustang GT convertible is 10 years old and has logged 14K miles (no typos in above). The correct oil viscosity is 5W-20. When I switched from mineral to synthetic oil I noticed that a small oil leak commenced. 2) I tried Toyota 0W-20 synthetic on my 2004 Prius a couple of years ago. The odometer was probably at around 70K miles (now at 106K). Prior to that switch the engine did not consume noticeable oil between oil changes. After that change the engine consumed more than 1 quart of oil after 5K miles. I went back to 5W-30 synthetic oil but the engine has continued to consume oil although at a reduced rate.
From my purely selfish point of view I encourage the OP to go ahead with the switch and report back his/her findings to add to our so far sparse data.
I have a similar story. My 08 Prius always got 5k mi. oil changes using regular Castrol 5w-30. It never used a drop between oil changes. At 80k. miles a different place did an oil change and used Valvoline synthetic. The car used about a quart in 7k mi. After swithcing back the car used about a half a quart or maybe a little less til 100k when I traded it in.
