Gradual decline in fuel mileage

My early 2010 (one of the first 2000 built) was getting 50+ MPG until the last few months and now is in the 47-48 MPG range. I have a Yellow Top 12 volt battery on order and will post the results once I install it.

 

Most likely reason is heavy ac use during the summer, not the battery

 

Year round variation in MPG (presuming no change in driving habits) can be attributed to...

1. Change in gas. Gasoline is formulated differently during different times of the year, and this can have a noticeable impact on MPG.

2. Change in temperature. Aside in how you may or may not use your A/C or heat, colder air is more compressed and yields more horsepower, but sometimes at the cost of fuel efficiency because the higher concentration of O2 = more fuel injected for balanced combustion.

3. Tire pressure. If you stay on top of this, it shouldn't matter, but colder tires run differently than hot tires, and it goes without saying that the roads don't warm up as much in winter as they do in summer.

You really don't know until 2-3 years of monitoring MPG and driving habits if it's a fluke of that time of the year or something larger going on.

 

you dropped 6-8 mpg after a fuel system decarb, i wouldn't blame the car, i would blame the decarber and demand they fix it.

 

have you tested the 12 volt battery? she might be running low.

 

i understand your frustration, it is difficult for us to help you through the internet.

 

Just to rule it out, have you checked the oil level on your dipstick?

Dealers are notorious for over filling the oil when doing an oil change.

I can swear that I'm getting much better mpg after discovering an overfilled crankcase and draining out the excess oil in my V6 Camry.

To make matters worse, the dealer told me my throttle body needed to be cleaned. I'm pretty sure it got dirty from the increased crankcase oil pressure from the dealer overfilled oil changes.



SCH-I535

 

Did they check for brake drag? You can do that your self, pretty easy. Even if you've just got the scissor jack. Chock the front wheels, at least one side, both front and back of the tire, then release parking brake. Raise one rear corner (or the whole back end, if you've got a floor jack, at the central rear jacking point). Give the wheel a spin. There'll be a little drag, it being a disc brake, but it should spin through a revolution fairly easy.

Don't forget to remove the wheel chocks before attempting to drive.

Or dead simple: immediately after a longish drive, feel the hubs, see if any are markedly warmer. Also, feel with the back of a finger the actual disc, reaching through the wheel spokes, if you can. Be careful, they can get toasty. Just see if all four corners are in roughly the same range. If anyone is markedly hotter, could be a problem.

 

did you have the inverter recall? that seems to have caused some mpg problems.

 

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!