I did the math on getting new (more efficient) vehicles and you never get your money back - even at $5.00 per gallon. Insurance and the RIDICULOUS price of a new car make it impossible to make the numbers work. So, unless you just have to have a new car that smells good, keep the old one.
Let's just say I drive trucks with at least 8 cylinders...maybe more.
I will keep them until the wheels rust off.