Building on what Arrow said, you can buy a can of Seafoam. Follow the bottle and add it to your oil and drive it one day, then that afternoon while oil is still hot, right after you cut the car off pull the oil plug and dump the oil. Then run a cheaper regular oil for say 1500 miles and then dump the oil again and then switch to a good Syn oil, and good filter. Then run this oil say 4k miles and dump, see what it looks like if still amber i would go to at least 6k miles on the oil, and do the same thing you being the judge on how long to go. Syn oil can easily go to at least 9K my opinion on regular Syn oil, they have some extended ones but i personally dont want to go that long no matter what. Make sure you check your oil level regularly though!!! The syn oil has some benefits. In an engine known to have a sludge problem, syn wont sludge. Sludge forms from dino oil that is over heated and old/ breaking down and forms a thick gunk that coats everything and constricts pasage ways starving the heads and bearings of oil. Syn also will clean old deposits over time, so in theory the longer you use syn, to a point it will clean up that old engine, this is why you want a quality filter (i use puroloator pure one) as they have more filter media in them, allowing them to catch more crud before they totally plug up.