If it's still under warranty, I believe you have to use 5-w in it to keep from voiding the warranty, the owners manual and the oil cap should tell you which to use. If no warranty, pretty much like Mud said, just personal preference. I try to change mine every 2500 miles, but if you don't do a lot of hard driving (off-roading) you can get by with every 5,000 miles. The most important thing you can ever do for your engine is to regularly change the oil.......especially when you consider that there is only a few thousandths (if that much) of an inch of oil keeping the metal from rubbing on metal.....words my daddy taught me at a very young age to live by.