My old 1990 Ranger with a 2.9 gets Chevron Supreme Blend 5-30 and seems to really like it. I am not sure if the original seals would resond well to full synthetic oil. I am really not sure if it is correct to use our modern Ethanol gas in it. Nowhere in the owners manual says anything about fuel except that it has a 26 gallon fuel tank. Even the door for the cap has no mention except unleaded only.