I'll need to keep changing oil in my car every 3 months, just wanna know what will be the best option for me. I'm thinking of getting some good syn. / blend in the beginning of every year while using some cheapo dino oil in the other times. Is it a good idea or I should just feed the engine on straight dino oil diet? PS: The engine is a Ford 3.9 litre inline 6 and factory spec ask for 40 / 50 weight multigrade oil.