I have a 2005 Prius with daily 33 mile commute and 20 miles during weekend. My area is San Francisco with mild climate. I was able to stay 60+ MPG (record: 63MPG for 630 miles/tank) for my first 45K. After I changed tires (Bridgestone?) at Costco 1.5 years ago, the MPG dropped to 56 immediately. I then understood tires matter a lot in MPG. I regretted but couldn't do anything about it. About a few weeks ago, the MPG dropped again. The MPG became 51 at my best effort. I have had no changes in my driving style for 59K miles so far. I guess it's the classic Prius style. I read a few similar posts. They are about cold temperature and 12V battery. They don't seem to apply to my case. What could be the problem? And how can I fix it? I really don't want to drop to under 50 and want to get back to somewhere around 60 like before. Thanks!
Why don't you suspect the 12V battery? Is it new or have you checked it? Otherwise... any reason to suspect alignment may have gone out? Like a bad pothole or curb strike? That's it, I'm out of theories! - D
12V battery can be the cause. However, it showed 12.2-12.5V when I checked the signal after hours of parking yesterday. It looked like okay. I don't notice the slowdown about the windows as discussed in other post. Perhaps it's the start of the battery problem to cause the recent sudden 5 MPG drop (from 56 to 51)? Maybe it's still early to replace it? Should wait until when it becomes 11V or the MPG drops to low 40? Appreciate any pointers. Thanks.
Those battery values are fine. What are the tire pressures? Did *anything* else happen or change at the same time, or just before? An oil change and you haven't checked the level since? Drove over a tree trunk? 300 pound guy joined your car pool?
I did oil changes at dealer. They adjust the tire pressure and rotation. Nothing unusual that I could notice. I drove slowly and smoothly on highway commute. The MPG drop happened suddenly from 56 to 51 one day and 51 since then. I seemed to feel the engine noise louder and the engine seems to work harder than before. Now I'm near 60K and looking for oil change since I have used all the dealer coupons.
You have not indicated what tire pressure you run or even whether you have checked it since the drop, so that's an obvious elephant in the room. Oil change perhaps coincide with the drop? Dealer could have over filled or used 30W. You could have a dirty MAF sensor or a clogged air filter?
Absolutely. *Always* check the oil level yourself before driving away from every oil change. Go check it now. Everybody makes mistakes; mistakes with an oil change can reduce MPGs or wreck the engine. And check the tire pressure yourself at least once per month. You can buy a nice gauge for about $7. If not told otherwise dealers usually set tires to the factory pressure; higher pressure, up to the max given on the tire sidewall, gives a harder ride but noticeably increases MPGs. And of course the dealer might have set them too low, or there might be a slow leak, or the outside temperature might have dropped 20 degrees,...
12.2-12.5 V is not fully charged especially if the car was just recently turned off. The battery should be 12.6V or a little higher. I would have the battery checked.
