I've changed my drain interval from 3k to 5k miles (topping up about every 1k miles when needed), when I changed to Mobile 1. I changed the interval based upon findings of this very interesting website:

http://neptune.spacebears.com/cars/s.../oil-life.html

Looking at the latest data, Amsol appears to be superior to Mobile 1 (however we should wait until the end of the trial to make a definitive judgement). I'm also interested in what findings they will have using a regular petroleum based oil.

I agree with all that Joe states in the thread above (I based my decision to go synthetic on frequent talks with him on the subject). I do think that the "every 3k miles" that we have ingrained in our car-crazy mentality is caused by Jiffy-Lube hype - however for the cost isn't it worth the extra insurance?

Since 5k is still within the recommended interval for our trucks/engines, I think the better quality oil allows me to extend the interval a bit. I would not recommend going to the extremes that they do in the testing on that site, however.

-- Best, John