[Wisha Haddan H3]

They tell you 3-4000 miles to protect their liability and get more business, but when you actually need it depends on your driving style.

I love synthetic oils and use Mobil1 in my rigs. They have great additive packages, on top of a synthetic oil with uniform (instead of average weight) molecules, engineered for consistent viscosity, an extremely low pour-point and high heat resistance.

Clean, pavement-driven synthetics will last until the additive package dies. So it could easily be 10-15,000 miles on highway. But if you drive on dirt roads or wheel a lot (especially with a K&N filter imho), you may need to change it sooner, because of dirt in the oil.