Recommendations for 90/10 Highway-City

[zerosoma]

Prius; 600 miles a week on average, drive an hour to work and an hour back.

I drive 10 minutes in town, I divied it up and it calculates to about 90% highway and 10% city.

On regular Conventional oil, when should I optimally change? 5k? 10k?

 

[CATERHAM]

Using a 5w20 conventional I'd stick with 5,000 miles.
If you want to optimize your OCI have a used oil analysis with TBN done a 5K to see how much longer if any you can go on the dino.
I think running a synthetic bought on sale may be the more cost effective approach to maximizing your OCI.

 

[KrisZ]

Good candidate to take Mobil 1 Extended Performance to its maximum advertised distance.

 

[Barkleymut]

Do you enjoy changing your oil? If so then stick with 5k OCIs, if not then I would bet my house on you being fine at 6K or maybe even 7K OCIs. I drive almost all of my miles on the highway and just enjoy knowing that my engine is as clean as possible so I always change at 5k.