The ONLY way to tell if you can truly use the oil that long would be to do an Oil Analysis using someone such as http://www.blackstone-labs.com/ What you would normally do would be to order a testing kit from them and during your next oil change you'd remove the required amount of oil and send it off to them. I DO NOT recommend going the full 15k unless you KNOW you can do so, for the Blackstone Testing start off around 5000-7500 miles and send them a sample. If you request it and I believe it is their norm now they will tell you how much life the oil has remaining! Driving style, Conditions, Altitude, Etc ALL have an impact on what is in your oil and how long it will last when it's analyzed.

Do yourself the favor and have it tested by the professionals, Piece of mind is very hard to replace with anything else.

-Froth

 

thanks

 

I change my oil every 6K miles and use fully synthetic I only drive my G35 5-7K miles a year.

 

If what you say is true about your change intervals and yearly milleage, then you're basically changing your oil only once per year or less. I'm pretty much almost in the same boat as you as far as milleage per year is concerned... but I would not feel too good about leaving the same oil in there for over a year. I usually do my oil like 3 times a year depending on how much I drive... and since I do a lot of short trips, I like to get it out of there by 3K since I'm on that less than 8K miles a year on the G35 driving cycle. Oil changes don't cost much, and you might end up with some excess carbon/sludge buildup inside the motor from the combination of long milleage intervals between changes as well as really long time periods of the oil just sitting there in your motor.

It's just a recommendation, but like I said... oil isn't that expensive, and it's probably not a bad idea to veer on the side of safe rather than sorry here.

 

Thank You!!!!

 

+1, that's the good stuff.