You want your car to last, so you treat it right. That means regular oil changes, weekly washes, seasonal rustproofing and, of course, nothing but premium gasoline with every fill-up. Only, in some ...

My car requires premium gas, but I filled the tank with a lower grade gas, causing a knocking sound. I then put in an octane additive. How long does it take for the knocking to go away? – Brett Octane ...