I purchased a used Town & Country in April 2010. It was a 2009 with 35k miles. Since the purchase I have documented every single penny paid out as well as tracking miles per tank and miles per gallon. During the month of September 2010 I filled up my tank seven time with an average of 25.83 mpg for the month and in October 2010 I also filled the tank seven times with an average of 25.87 for the month. On October 30, 2010 I purchased new tires and got an alignment. When I filled up on November 3rd, 2010 my average for the tank was just 20.93, a five miles per gallon drop. What would have caused this very unexpected and massive drop in my miles per gallon?
Well, it has been a month and seven tanks of gas later. I am averaging 20.86 mpg with my last tank at 19.18 (Yuck!). I spoke with the tire folks, the alignment and the tire pressure are fine, they do not know why the mpg dropped as it did. Took it down to the dealership and they said that everything is working just fine, could find no issues but also could not explain the drop in mpg. I also put a new air filter in, it needed it but with no impact on the mpg. A man from my church suggested that I find a set of original OEM tires and put them on for a couple of tanks of gas to see if there is an issue with the composite materials used in the new tires that is having a dragging effect on the pavement causing it not to roll as easily as the originals tires. It kind of makes sense but not to the tune of 5 mpg. I will test it out and give another update near the end of December.
Last edited by Gibster (11/29/2010 10:33 PM)
I would drive a little while longer. Just checking the mileage with the new tires and wheel alignment with just one tank would not be accurate. Drive for another month and then compare the numbers.
The tire pressure could have been different or higher then the old tires. If the tires were at let's say 35 psi and the new tires were filled up at let's say 28 psi, then the difference will affect your fuel mileage.
If the wheel alignment was performed and the machine was not calibrated properly, then the alignment could cause a little more drag on the car and wear out your new tires quicker. It's not common but could happen.
Both could be the difference in the loss in mileage. Talk to the repair shop that sold you the tires and see what the difference was between your old tires and the new ones and also check your tire pressure. A good tire pressure should be about 35 psi per tire. Also you can have the wheel alignment checked just to be sure.
Drive for about a month and then compare your results with your old results before you make any decision to talk to the repair shop.