Hello Everyone, I am sure this has been discussed but I cannot find a thread so I am posting my own. I live in Phoenix AZ and I have notices on the hot 100+ days my Prius takes a pretty big hit in MPG. I normally average 55MPG but after the car sits in the sun all day I have a hard time getting the car to maintain speed and get above 40-45MPG. I have read about the cabin temp playing a role but even after driving for a while and the cabin getting to a comfy temp it still seems the Prius is sitting at 40 -45 MPG. I know that is not that low of MPG but on cool days I have no trouble maintaining 55MPG. Has anyone else experience this? is it normal? Am I whinning about nothing? A co-worker of mine says he too takes a hit in MPG on hot days but his is barly notiable (at least that is what he says) to me %20 is definitely noticable. Any thoughts or suggestions would be greatly appriciated. Thanks
I hear you. On Sunday (105F) and Monday (110F) I noticed (via MFD) that i was dropping to 45-46 mpg. Then it cooled off quite a bit, and I had a few runs of around 50 mpg. At extreme heat, the AC runs almost constantly, drawing energy from the traction battery. The recharging requires more ICE run time, thus a bit of a hit. Just my $0.02 worth.
But in those very hot days, you need to keep the cabin temp down as it cools the battery also. Some people turn off the air, not a good idea.
Root is correct about the AC, with the effect being greatest at low speeds when the ICE would otherwise cut off when not needed for propulsion. In addition, the car likes a relatively cool hybrid battery. If it gets too hot, the car will give greater preference than normal to running off the ICE, making the car feel sluggish. I had an episode or two last summer where, in 100F+ heat, the ICE lit during an S4 glide repeatedly at 26 MPH -- behavior I had never seen documented before. See this for more.
I'm agreeing with Jimbo here. We don't get up to Arizona temps around here, but when it's hot, I make it a point to roll down the back right window from time to time in order to get some fresh air in the vicinity of the battery vent. I"m not sure what to tell you about possibly fixing the problem. If you run the A/C you will take a mileage hit from the battery discharge. If you don't you will have a hot battery pack which is impacting your mileage. Perhaps you can run an air duct from one of the dashboard A/C vents back directly to the battery vent.
OK that is kind of what I was figuring. I keep the AC running when it is warm 85+ and figured as long as the AC is keeping the cabin cool the miliage should be good, but it is true that the AC will have to work harder to keep the cabin cool on the 100+ days causing more draw. It also does not help that the prius is so windowy (Bushism) I think that keeps the back half of the Prius considerably warmer than the front half since there are no AC ducts back there. Thanks for the input I just wanted to make sure I was not nuts or doing something wrong. It would be nice if there is a way to fix it but I have a feeling it is just the nature of the beast.
