How do you determine what is a good

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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?
 
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Try a 10w-30 if you're set on 30 weight oil. It may hold up better then a 5w-30. If it doesn't start consuming it at or before 3k ..extend the drain. You may be in severe duty territory.
 
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To be accurate with your OCI you would do a UOA. But with an oil change at $10 (DIY), it's too easy to just change it ... So where does that leave you? IMHO, your observations are all on mark. Anyone in tune with their engine can tell when it's beat up the oil. The SM oils should take you 4 to 5k - likely. Also, delve into the UOA archives! Search on Subbie Outbacks. Here is one (Walmart synthetic): UOA
 

kendogg441

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well, what should I do then? I'm new to this forum, not sure how and what to search for yet. Should I simply continue on my 3k mile change intervcal till springtime, when I may be close to my 20k mile marker where I wanna switch to syn? Then test it out, go 5k, then do a UOA?
 
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I'd try another brand of dino, Havoline would be my choice. I ran Castrol GTX in my mazda's 1.3 for years and I observed the same symtpoms as you are. Those engines are particular with HLA's and around 2700 is when they would start to tick with Castrol. I can run up to 5k with Havoline with no problems with HLA's, gas mileage or driveability. Some engines run better with different brands, for example my parents chevy 3.4 and our toyota 1.6 doesn't care what you run but our festivas and f150 5.4 seems to perform better with Havoline.
 
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