My 2006 Solara used to get 32 MPG on mixed city and highway driving, but about 1 month ago, I noticed it was only able to do 27-28 mpg. At the same time, the engine noise becomes noticeably loud at highway speed and I feel it’s losing the normal power because it is hard to even push it to 80 mph. What could be the problem? Thanks.
hello, have you done a tune up (spark plugs, wires, etc…). How many milesyou have on the car and any recent repairs done?
Thank you.
Except regular oil changes, I have not done a tune up. It has 31000 miles on it. Could it be that one of the cylinders is not working?
If a cylinder wasn’t working the car wouldn’t be driveable. You don’t have overdrive locked out do you?
If you do not have any Check Engine Lights then the likely case is there is nothing that can easily be addressed or at all.
Make sure your tire pressure is proper and realize MPG does drop a bit in the winter. You cannot achieve 32MPG going 80mph, not going to happen with this car.
You may have accidentally disengaged the overdrive, and the engine is running at higher speeds than it used to.
Is the transmission shifting into overdrive (OD)?
Well going 80 mph is going to hurt the mileage 
A month ago likely the weather was warmer. Today colder weather and likely a switch to winter fuels, could explain the difference in mileage. It would not do much towards explaining the rest however. You might want to have someone check to see if there are any error codes stored in your car's computer. Some auto parts stores will do it for free.Call me silly. I am really confused. I cannot find any engage/disengage button or switch for overdrive, or display for OD, and I cannot find any relevant entry about OD in my owner’s manual. But I looked it up on the internet, it says the transmission is 4 speed with overdrive. How do I know if it is in OD? BTW, the model is 2006 Solara SE V4, automatic, and I live in Michigan.
Thanks a lot.
When you are driving about 40-45 mph or so on a level road with no cars immediately behind you, move your shift lever from “D” (or D4) to “3” (or D3).
If you can feel that the transmission downshifted, then that means that you were running in 4th gear (overdrive) prior to the downshift, and you can rule out an overdrive problem.
If you did not feel a downshift, then you have found the source of your problem, and you will need to have the transmission checked by a qualified, competent transmission specialist. Please note that the words “qualified and competent” are never placed in the same sentence with the words AAMCO, Lee Myles, or Cottman, nor is the word “honest”.
If you need transmission work, go to an independent transmission shop that has been in business for at least 3 years.