I have to agree with Raque. Synthetic flows better sure, but as far as extended oil chnages, even if you spin on a new filter, you are still circulating oil contaminated with fuel and combustion gases. My family has had engines hit 175k to 195k(and still going) with real oil. The most I have hit is 165k...and on a Chrysler yet before I traded it in. Change the oil at 3k intervals and save yourself the $$$.

After that I have to admit, I am running a synthetic in my diffs simply because they are not effected by a combustion process.