[QUOTE=PSJ;3037006]If you changed your oil @10,000 miles using synthetic vs dino @ 5,000 it seems like a wash $$ wise unless we can prove synthetic is better for the motor. But if you went in to the Dealer with an engine issue with the practice of using synthetic and changing @ 10,000 miles, and had all the service records, your claim may be denied because the manual states 5,000 miles/6 mo, for oil changes, with no exception of synthetic oil use and extended miles/periods stated. However, "tests" and many agree synthetics do last longer or do not break down like dino. All I know is as many have mentioned, this a small part of maintaining a vehicle, but when I change my dino oil between 4-4500 or less miles, it always looks "tan" or not worn out.
Going 10K is a little better than a wash... but a lot better on convenience. It also has a lot of margin: if I can't get to it until 13 or even 15k I have a really high probability it's still good oil. I don't have a garage so DIY oil changes in winter are completely out of the question.
Agree with the issues about warranty at 10k changes; but two things are very much in my favor. First: Toyota doesn't seem to care about oil change records if the transmission or diffy grenades (as they shouldn't since it has NOTHING to do with the engine oil.) Second: the engine in any modern auto very rarely fails when it gets proper maintenance. It just doesn't happen (unless it's GM, I guess
). So I find this risk very low from that perspective.
Lastly: I know you should NEVER go by looks of oil! Looks tell you NOTHING. The story of oil aging is in mechanical properties (film strength and viscosity) and it's chemical properties (TBN, or ability to deal with acids) primarily. So, I don't care about how dark it gets in use! Diesel oil can be tar-black within 500 miles of going in service: it's still perfectly doing it's job protecting the engine!
The thing about synthetic oil is: they maintain their mechanical lubricating properties, even in extreme service, longer. And since they ARE longer lasting, mfr's can make the addy packs longer lasting too. But IMO, it's all a total waste if you don't extend drain intervals since, in basic protection, any API SM or SN protects pretty much as well whether it's synthetic or dino.