dino oil is always changed at "X months or Y miles, whichever comes first" - I understand, because the additives break down over time regardless of how many miles.

what about full synth oil, like the Mobil 1 I just put in? Does this have both a time and mileage limit, or can I just change it when I hit 5K even if that's next spring?

 

Check this

 

I go 10,000 between changes although I have considered going 15000 with filter changes every 5000. I do notice that at about 8000 miles my oil pressure goes up just like in the article so I've stuck to 10000.

I did an oil analysis after 10000 once and the results came back that I should leave it in the engine and send another sample in another 5000 miles. I think the key to extended drains are using a quality oil filter and changing it every 5000 or so miles even though you leave the oil in.

 

very interesting, but mileage based

what if it takes me 18 months to go 10K miles?

 

Sorry. I change it at 1 year no matter what. I did a lot of reading on synthetic oils when I was looking for an oil for my TDI Jetta. I settled on Mobil Delvac 1 which is far superior to the Mobil 1 I use in the 4Runner but very hard to come by (Delvac is a diesel oil). Most people doing a lot of oil analysis' agreed that 1 year seemed a reasonable number although I don't come near that as my wife runs about 25000 miles a year. That is why I needed the 52 MPG that the TDI delivers.