I am a service writer at a dealership in KC. I have a customer who has told me that once you start synthetics in your vehicle, you should continue synthetics for the life of the vehicle. Is there any truth to this? I told him there are 100 opinions for how synthetics should be used and there is no concrete answer.
Castrol, mobil, and Royal Purple all have 800 #'s on their bottles. I called, and every manufacturer said there is no harm in switching back and forth. They said you can top off w/ regular oil if you are a quart low. They also said you can go around 6000 mi. between changes, but have to still change the filter at 3000 mi. Of course add a quart if you change the filter.