Synthetic vs. Nonsynthetic oil

Ok to answer your initial question...no, you can go between synthetic and conventional or even mix them if you want. Synthetic blend is a scam...most of them have only 8-10% synthetic in them, now there are some 50/50 mixes out there. what matter most is that they meet your vehicles requirements which will be on the back of the oil container and in your owner manual. you want to meet or exceed them. synthetic oil gets the top of your motor faster and reduces friction and also flows at far colder temperatures, why. conventional oil has waxes in it which means there is water and water freezes. where conventional may flow down to -20 below, synthetic will flow to -40 to -50 below. in the end no matter what you use if you pull the dipstick and your oil is dark brown i dont care how many miles are on it, it cannot hold any more "dirt" particles and needs to be changed. what people fail to notice is in there owners manual the normal maintenance schedule is for people that do 70% or more freeway driving. freeway driving is what they mean when they say under normal conditions. if you drive mostly in the city that is considered severe duty and you should not go more than 3k on a oil change. OIL CHANGES ARE THE CHEAPEST MAINTENANCE YOU CAN DO FOR YOUR VEHICLE PERIOD. what are my qualification.....how about 2k plus cars that i have helped service and counting. please help me out and go 5-7k miles on a oil change and listen to you manual and ill see you in the service drive....bring the check book