MPG Dropping

The mileage on my 2010 dropped from 56 to 49MPG suddenly about a month and a half ago. I knew something was wrong but figured maybe poor fuel quality. I fueled up again once the tank was empty, and once again 49 MPG. That ruled out the fuel quality. A week ago the problem finally revealed itself. The car took a few tries to get into ready mode and almost left me stuck. I tested the 4 year old factory battery and it was at 12.3 volts and 68 CCA. The 12 volt battery had failed. I bought a new fresh battery from Team Toyota in Glen Mills, PA for $179 after military discount. After I installed the new battery, 56 MPG again!

 

If you also had a recent oil change, make sure they used 0W-20 and that they didn't overfill. Dealers are notorious for using the wrong weight and amount of oil.

 

If the oil weight and level are fine, I would run a tank of gas with Techron.

 

I have updated the main thread with my experience using 0W20, 5W40 and 5W20 fully synthetic oil

 

I have a 2013. I am running on 17 inch rims. I average about 45 mpg. I have almost 25k on the car. I don't know how people are getting 55 mpg average. Can it be my 12 volt battery? Mine is reading 12.3 Volts, just under 12.4 volts as you specified. I read this of a scangauge II when vehicle is turned off.

 

not everyone get 55, it depends on your commute, your terrain, your weather, your driving style, and the 17's are definitely costing you something. the battery sounds a bit low, but not enough to hurt your mpg's. you have to check it cold, after sitting for a few hours with the car off.

 

I was averaging about 57 mpg according to the trip computer with my liftback Five and its 17 inch wheels (I mostly take suburban backroads to work, and do 60 mph on the freeway).

For a few weeks it was only getting maybe 52 at best. Then I checked my tire pressure, and found out it was only at 32 psi cold (it sat for 3 hours before I checked). Silly me, I filled them up to 38 front, 36 back (I'm happy with this range, as some of the roads are bumpy and we have potholes in the winter time, so I don't want to risk a blowout with higher psi).

While I couldn't exactly drive the normal route I take to work because they closed part of the freeway off for construction, I was averaging 57 mpg again with the tires filled up. I definitely noticed it was allowing me to coast longer again after filling them up.

Yeah, yeah, I know, I shouldn't of let them get that low lol. Will definitely keep a closer eye on it from now on.