After about two years of averaging about 48 mpg (almost all suburban driving), I was suddenly barely hitting 37 mpg. It's been that way for about a year now, and I'd just about given up after trying everything I could think of to make it better (non-ethanol vs ethanol-added gas, messing with power modes, setting all climate control manually). When I took it in for service last week, I mentioned to them that this huge drop really bothered me, and frankly I found it unacceptable. While doing the tire rotation, they told me a rear brake caliper felt "sticky" and for $74.99 they could take it off and clean it, and it could very well solve the problem. I figured that cost would be worth it in the long run if I'd get back all that lost mileage. They told me when they took apart the rear brakes there was indeed quite a bit of buildup, and that they cleaned and reassembled everything. A little less than a week later and I'm back up to averaging in the mid-40s. I don't expect to get all the way back up to 48 because I did get new tires in December that I'm sure have taken it down a bit (but the problem had started last summer, probably around June or July). Anyway, just thought I'd share in case anyone else had noticed a sudden drop and couldn't find a cause!
Thanks for your post. Many people believe that when the mpg's drop they suspect it is the 12 volt battery. Checking the brakes now would be another option.
I'm a little curious as to how you can be dragging a foot on your car for a YEAR without serious brake wear. However (comma!) if the dealership disassembled, cleaned, and then reassembled the caliper for $75, then that's not a bad rate all things considered. I'll be curious to see if the improvement continues. When I was experimenting with how good/bad I could do mileage wise, I filled 'my' (company car) 2010 up and then for an entire tank I drove it like I stole it!! I got something like 43 MPG. Barely hitting 37???? Wow.
I would have love to see the break pads etc... the breaks needed to waste just so much energy they should have worn tremendously over a year ... I can not see any way this creating this much mpg drop ... the only ONE thing I would think of that somehow this was interfering with regenerative breaking. Like somehow switching/giving up regen and go to friction ... but this would be rather the result then the cause of it ... But this is interesting ....
I know! It's been ridiculous. I moved from Illinois to Nebraska last summer, but the weather and terrain has been pretty much identical so I didn't think that made a difference. All the gas back in my neck of IL had 10% ethanol, whereas here only the lowest grade does, so I experimented with getting the 87 with ethanol and the 89 without it and it didn't seem to make a difference AT ALL which surprised me a little.
unless your having some pre-ignition problems, not likely in a Prius engine, then moving from 87 to 89 won't change your MPG. Moving from 10% ethanol to 0% ethanol might.
I actually misspoke, here ALL the 89 has ethanol (and is generally 10-15 cents cheaper per gallon), it's the 87 that doesn't. So it wasn't that I was changing the octane on purpose, my goal was to test ethanol/non-ethanol and the octane change was unavoidable. The first two years I drove the car, I was in an area where all grades of gas had ethanol no matter what, so it was always 87 with ethanol. Now I have the option of 87 without or 89 with. I have been going with 87 without but it didn't help the low mileage I was getting.
