I got the oil changed in my GXE last month. Before the change, it was averaging almost 350 miles per tank (30-31 mpg). I believe the car had been using 5W-30 before this change, but I was given a bunch of liters of All-Climate 10W-30 by a friend and decided to have the mechanic use it up for this oil change. In the last month (October) I've had a noticable drop in gas mileage, barely making it over 300 miles before refilling. Would 10W-30 actually cause this sudden decline in gas mileage? (I haven't looked at the spark plugs or air filter yet, and it doesn't seem cold enough yet to be the change of season.) Thanks much guys!
Nov 2, 2007 at 6:08 PM