oil change interval for your particular driving? I own currently an '05 Subaru Outback Sport, 2.5L non turbo. Right now, I do the normal 3k mile oil change, with castrol GTX 5w-30. the car has 12k miles on it,a dn I plan on switching to a synthetic near 20k. Now, I do do alot of quite 'spirited' driving. My car see's redline almost daily. unfortunately, I don't plan on changing the way I drive. Sometimes I'll hit some of the back roads at 100+ mph, shifting hard, keeping the rpm's up, ya know, your basic performance driving. I've noticed that I can tel with teh GTX that it doesn't lubricate quite as well after about 2000-2500 miles on it. You call tell, you can tell the way it idles, you can tell by your fuel mileage, and it starts to consume normally before 3k miles. It's always been my feeling that by the time an engine starts burning oil on an oil change, that that oil is realy not doing it's job anymore. Am I right? Also, the way I tend to drive, I don't know if I'd want to go more than 5k miles on synthetic, not becuase I may wear it down, but, because I worry about gas-logging the oil after so many miles. Whats the consensus here, fella's?