i run amzoil full synthetic and someone told me it wasnt good to switch back and forth between regular and synthetic but after my valves started leaking and it was using a quart every 500 miles i had to look for something cheaper til i got my new motor and the dealership said i could just start pouring regular oil in it and assured me it would be fine i couldnt really tell a difference except i was saving about 4 dollars every 500 miles