and Amsoil is a thousand times better then RP.
i have used amsoil for all my cars since iv started driving and it keeps every thing REALLY clean. when i change my oil it is still semi see threw after 4000+ miles.
trying different oils, going from amsoil to regular, they have different properties and don't mix. I have never had a problem, but know of 3 people at U of D mercy who blew there engines!! they had all heard that amsoil wasn't the best so they all switched at once, and by the end of the year, they had blowby!! I run amsoil in my toyota, but will not switch back as i don't want to have an issue. I have heard it is good for really high mileage!!
The problem w/ amsoil is that once you use it, you really shouldn't go back, so you can get stuck w/ it!!