So I just changed my oil on my new truck. I went with the Mobil 1 extended performance advertised to go 15k as well as their oversized extended interval filter. Does the guage on my truck move down towards "change oil" based off time or milage or what? Or does it actually analyze the oil? If based off milage is it based on the old 3k mile rule? I plan on changing it at 7k or so.

roe