Normally my 2011 Prius sees a drop in full economy as Chicago goes to winter blend fuel (from 52 mpg to 44 mpg) but comes back in the spring when we switch back. This spring it has not come back as expected. My car is nearing the 100k mile mark. I am a fanatic about changing the oil. Any suggestions as to cause? The only things I can think of air filter dirty (but nothing was said at last oil change), low tires (checked fine) or maybe batteries going bad. I would think that as the drive batteries begin to fail they just don't store and hold a charge as well so you have to use the gas engine more, leading to lower mileage. Any thoughts would be appreciated. Ed
I am not sure if summer blend is totally blended in yet, but that's probably only 1-2 MPG difference by itself. Chicago is also reformulated gasoline which is a little less energy too. With reference to RFG maps, if you live on the border you might get a little better MPG filling up outside the RFG zone. Check 12v is always a first step. The HV battery minor degradation does not seem to impact MPG. Basically older Gen2 should get same MPG as newer Gen2 except if something is wrong.
I never notice a big drop in winter, if any. And what there is could be in large part due to lower ambient temps, conditions. (Disclaimer: our recent "winters" have been really mild.) Check the 12 volt battery voltage with a digital multimeter, post your reading? Also check air filter yourself? Pretty easy. Air filters don't have much impact on mpg anymore though, until they're near totally clogged, the computer adjusts fuel amount to suit air flow.
Check to make sure nothing is obstructing the cooling vent for the traction battery (located under the driver side rear passenger seat). This is an easily overlooked cause of poor mpg.
I'm seeing the same issue as you. This is my 3rd spring/summer with the prius, previously my drive to work was always between (65-61MPG and this spring so far its been around 48MPG. My average for my past 4 tanks has been 46MG which is bad considering for the past 2 years during spring/summer/fall I usually average 56-60MPG. I don't know what could be the problem. I checked my tired and they are filled as usual (actually added a little more air to see if it helps). The only thing that has changed is I replaced the cabin/engine air filters at the end of winter and put in FRAM ones instead of the toyota ones. I doubt though this would cause such a huge difference.
The spring has been surprisingly warm for Toronto. However this past week for some odd reason some trips have started to show normal numbers. Going to work I'm back down to 73 - 61MPG however some trips are still fairly high in the 50MPG range. This last fill up on the weekend is going at around 54MPG which is an improvement over the past 2 months.
This is kind of a long shot, but another poster here was suffering from low mpg, and it took a while to figure out why. Might find something worth trying for your prius in there. Jumped from 32 MPG to 56.6MPG - Heres How | PriusChat Another question are you doing a lot of short trips that are less than 6 miles and/or 15 minutes in length? Are you a lead foot and have to keep up with heavy traffic, or do you take quieter, backroads more often? Are you using the A/C much yet? With the weather warming back up somewhat in SE WI, my temps aren't much different than yours, and I'm averaging 54-58 mpg in my liftback. Keep in mind though I tend to do the speed limit, along with hybrid driving techniques such as pulse & glide. I also have 17 inch wheels, so that saps a few mpg for me as well. I also work 3rd shift and it's about a 19 mile drive one way. The drive into work is usually less busy, though there's some traffic on the drive home, but I still get around 51-53 mpg in the morning.
I've seen a similar Winter drop in mpg in my 2009 Prius, especially the last few years. Don't know whether to blame ambient temperature, winter-blend fuel, extra load running heater, etc. This spring for the first time I used MAF cleaner on the mass air flow sensor and saw an immediate increase from 44 to 48. Now I'm back to my normal summer mpg of 51. Could have been a coincidence with end of winter-blend or just increasing temperature, but you might want to give it a try.
