This topic is open to so much debate, you'll get at least 10 different answers to the question. I changed my oil with Ford's 5w20 at 500, 1500 & 5000. Then, I switched @ 6000 with 100% Synthetic 0W30. Personally, I'll stick with AMSOIL, they developed the world's first API rated synthetic motor oil in 1972.
http://www.advanced-synthetics.com/
Here's an interesting quote:
"Because a synthetic oil is chemically produced, there are no contaminants in the oil. By contrast, conventional oils contain small amounts of sulfur, wax, and asphaltic material that can promote detonation as well as varnish and sludge buildup. With no wax, synthetics will flow at much lower temperatures than conventional oils. In fact, synthetic oils are now available with viscosity ratings as low as 0W-30, as in Mobil 1’s new Tri-Synthetic blend or Castrol Formula SLX. These oils flow more than seven times faster than a conventional 5W-30 motor oil during initial start-up, yet at normal operating temperatures act like a regular Grade 30 oil.
An 0W-30 synthetic oil is capable of pumping easily at -62 degrees F and flowing at even lower temperatures. Conventional oils are essentially frozen solid at that temperature, so there’s simply no conventional equivalent to this new grade. There are 5W-30 conventional and synthetic oils, but even here, the synthetic has a real-world advantage: Mobil 1’s 5W-30 will pump at -58-degrees F, compared to about -35-degrees F for a conventional oil."
http://www.carcraft.com/techarticles/15378/
Note the temperature that 0W30 can flow easily at, -62 degrees. Now that's cold!
That is why I use AMSOIL's Series 2000 Synthetic 0W-30 Motor Oil
https://www.amsoil.com/storefront/tso.aspx
I plan to change my filter (AMSOIL or course) and oil every 10,000 miles. The oil is good for 35,000 but the filter is only good for 12,500.
At my 1st oil change, I plan to have AMSOIL do an oil analysis, just to check on things.
https://www.amsoil.com/storefront/oai.aspx
Well, that's what I'm doing. I have an 05 GT, put the AMSOIL oil in at 6,000 and I currently have 10,800 on the car.
Dave...