I've oil changed every 5k miles with 5w-30 full synthetic oil ($35 for 7 qt). It usually last a year since we don't drive a lot. After reading pelican's article about oil change and I'd like to know if I should switch to 5w-30 walmart super tech conventional oil ($15 for 7qt) at every 3k miles or use full synthetic every 3k miles? Mechanic told me that even synth oil can last longer, it's cheaper insurance to change often. I also heard BMW can develop issue with conventional oil.
I have 2.5 qt full synthetic left, I should NOT mix with conventional oil in the next oil change, right?
Last edited by yxd0018; 01-27-2013 at 01:48 PM.