Squeezing out 37.1 MPG around town

I have to try very hard to get 39.5mpg in my 2011 Prius with 187K miles.

The other day when it was over 90 degrees and I was sitting in my car just idling in the driveway with AC on full blast for 15 or 20 minutes....I checked the screen and MPG dropped to 32! It was taking way too long to climb back up and it was pissing me off so I just reset trip...So far the screen has been within about .8 of actual calculation by hand.

 

Well that would do it, why do you sound so surprised?

 

LOL --- Then the battery on dash (which I have been told a million times is meaningless and self-adjusts regardless of bars) dropped to 1 bar with 32mpg on screen....I was waiting for the motor to blow.

I'm sure with everyone else who seem to get nothing less than 45, 48, 51mpg....that when they idle with AC it doesn't drop below 40 and that is what I get when I'm trying my hardest to drive slow and use cruise control. I'm averaging low 39s

 

I guess it depends on how hot it is outside, and how often (and how long) one was just sitting in the car with the a/c on.

However, I do think there is something else going on with your car, I'd be extremely frustrated if I could only get 39.5 mpg (5.95l/100 km) in my Prius, i get sad at anything over 5.0 l/100 km (47 mpg). As you are not getting the signs of a dying battery, it probably is still reasonably balanced but has reduced capacity. Having said that it also could be a number of other things, outside of the HV battery.

 

Do you know if the 12V has anything at all to do with mpg? I swear I've heard people on this forum say that but my mechanic said that the 12V should have absolutely nothing to do with it...

 

Mostly no, or at least very minimal, but depends how the battery has failed. If your 12 V had a shorted cell and was therefore drawing a consistent heavy current as the car worked overtime charging nonstop, then may be there will be some noticeable improvement when you change that bad one out. But I think you are clutching at straws to explain your low MPG.

 

Around town means different things to different people. If you are talking about short jaunts of only a few miles or less the lower gas mileage is perfectly normal. The car needs to be run longer intervals to be efficient.

For example, my '08 has seen tank averages as low as 34 mpg and I expect the mid to high 30 range when the car doesn't see the freeway much for a tank. Especially when we run the a/c due to the higher temperatures. Overall, though, the average is 43.0 while we've owned it because it sees the open highway a fair amount of the time. It would be higher if that highway driving wasn't mostly at 70+ mph with the a/c on.

Looking at the 2011s at fuelly that are still being reported there are a few around the country averaging in the 30s. I suspect they are only being used for short trips locally too.

If you you fill up the tank and hit the open highway for a 100 miles or so what kind of average are you seeing?

EDIT: My car really is at 43.0 mpg lifetime. For some reason I've been unable to get my signature picture to display properly.