synthetic oil?

I have a 04 cav. And I put in castrol syntec oil. I was changing every 3000 but I was told that I am wasting money. How often do you guys change your oil those of you that are using the full synthetic oil. I was told that I should change it between 6-10 thousand miles. And what about the oil filter? Thank you

every 3k miles mobil 1 and new filter every time.. yes it is true you can run up to 6K miles without a real noticeable drop in oil level. I personally don't think its good for the car, but some people just don't care. Somtimes i go a few hundred of the 3k miles but nothing major. stick to what you were doing.

every 3k miles mobil 1 and new filter every time.. yes it is true you can run up to 6K miles without a real noticeable drop in oil level. I personally don't think its good for the car, but some people just don't care. Somtimes i go a few hundred of the 3k miles but nothing major. stick to what you were doing.
i agree

see the problem is the synthetic oils can last for 4,000 plus miles without breaking down, but the oil cant stay clean that long.