Oil Change: switching between oil types bad?

No problem. However you can furnish your synthetic oil to the oil change place and request them to use that oil.

 

I do the maint. myself as well, but I stick with synthetic. Switching shouldn't be an issue. Patrick is right, the oil change/dealership shops are just glad you came in. If you bring the oil, they'll put whatever you want in. I've had several offer.

 

Yes, use synthetic. Switching won't cause problems, but why do it? I waited until about 6k miles to use synthetic due to break-in of gas engine due to gas engine not running as much as non-hybrid. I used Mobile 1 extended, noticed better mileage right away. Went from about 52mpg to 55.o mpg last tankfull, and that was in the Seattle area, which is hill and dale a lot, both city and freeway. I also used best oil filter available. I am waiting for Amsoil to bring out a filter for the Prius that uses their new filter material, better than K&N, etc.

 

Yeah, used 5-20 I think. I think 5-30 or 10-30 is factory recommended for non synthetic oil, but since synthetic oil has significantly better film strength and slipperyness, I figure the 20 weight is fine. Also, it is in a light duty application, as you mention. Oil should be the least viscosity while maintaining film strength because it is very important for the oil to start flowing through the engine quickly upon starting and 20 weight will flow quicker than 30 weight. I think Amsoil is very good. I am not a fan of their oil filters, though, espcially after seeing test results. I prefer Mbile 1 or K&N, which peformed well in actually tests.