Hello everyone, been a member for a little while first time posting. I drive a 1989 chevy camaro with the 305 and i am currently running quaker state horsepower full synthetic 10w30 and change it every 5k miles. The car uses very little oil but it uses some at startup from the valve guides and seals. It has 190,000 miles on it and i would like to experiment a little bit. I want to know if i can safely run a full synthetic 5w20 in place of the 10w30. I would like the car to last 300,000 miles. Thank you.