How long should I go between synthetic oil changes? I'm hearing everything from 3,000 to 10,000 miles. The dealership says 3,000 as well as the mechanics at Firestone, but they stand to profit from this info. Others say synthetic oil last much longer than regualr oil and does not need to be changed as often. I realise that the type of driving I do has some bearing on how long I can go between changes but shere can I get unbiased advice on this issue?