I am seeing a huge drop in mileage due (from what I can guess) the high temps here in Texas. I was averaging 48-50 mpg (at pump) from November till May. Then it started going down. Currently its closer to 40 mpg, with the battery really not doing a thing till the inside of the car cools down. Same for the autostop. Course running the AC adds to the mileage decline as well.

I looked at the mileage database, and I don't see many others having the same issue, but its hard to tell where some people live. Any others in "hot" climates having low mileage issues due to the battery being "inactive" till the interior of the car drops below 90F ? Is this a 2006 model issue, or do others have the issue (2003-2005)?

Anybody come up with any suggestions? Larger fan across the battery pack (assuming there is one there already)?

Thanks,

Bob
2006 HCH
Hot Georgetown, TX

 

I'm lucky to live and work close the the beach in Southern California, where I don't need AC.
(I'd be more comfortable if I used the AC, but it is tolerable without it.)
Also, never have to park in the sun at work or at home.

Those who use AC may not know that hot weather improves your MPG, if you don't use AC.
I think it is because the heat is not carried away from the engine as quickly.
Some of the energy in gas goes into heating up the engine block.

 

I'm in Southern California, and despite running AC, my mileage has been slightly higher thanks to having temperatures of ~100 degrees recently. One difference is that the engine reaches "warmed up" temperature almost immediately, whereas the rest of the time it takes a few minutes of the engine running rich, and consuming extra fuel to reach ideal operating temperature.

A big factor is that the hotter air is less dense, so air resistance--the largest contributing factor to fuel consumption--is reduced as a result.

I used to have a problem with the battery overheating and not providing cooling, but that happened when the intererior temp was much higher than 90F, that sounds somewhat low to be causing battery overheating, although from what I understand hte major source of heating is long, extended periods of charging (adding that energy to the batteries is not completely efficient, so waste heat is generated) but I managed to mostly solve that by purchasing an aluminum windshield cover, and taking care to always park with the car facing the sun, so it is reflected away. I also run Max AC for "free" as I go down the hill from my house -- the hill is so steep that I would otherwise waste my momentum braking anyway, so running the AC hard for the first several minutes costs me absoultely nothing in MPG, and keeps the batteries from heating up while charging heavily. It also makes the car cold enough that the AC doesn't need to work very hard for the rest of my trip.

 

Georgetown,
I've noticed the same thing in New Orleans.Our MPG has dropped about 3-4 because of the unrelenting heat and humidity.I would guess Georgetown TX is pretty much the same with slightly lower humidity. I have attributed it to the AC use, not to the battery needing to be cooled.
When a vehicle in S CA sits all night, the temp of the entire vehicle probably drops to 60 degrees in the summer. Our low temps are 75-80 around here, so the car never gets cooler than that.By 10 am the interior air temp of the Prius is over 100 degrees(yes, I measured it) despite the outside temp being only 85 degrees(all that glass and the black color don't help).
Now there is a sweet spot-temp wise-around mid April when the outside temp is 70 or so during the day.The car motor etc heats up quickly(it has been sitting in the sun, so it is fairly hot already), so it can get in EV mode in 3 miles or less, but it is cool enough so we don't need much AC. This is much like S CA in the summer; their humidity is low enough that 85 degrees is roughly like our 78 degrees with high humidity.Their motor is preheated, but the heat/humidity don't require full blasts of AC.
You aren't alone Georgetown-TX, LA, Miss, Ala, FLA and parts of Georgia sweat with you.
Luck,Charlie
PS I have scangauged our non hybrid vehicles-same story-we get peak mpg in the spring and fall months when it is warm enough for short ICE warmup, but not so warm it requires full AC.

 

I have always seen quite the opposite result. When you look through the database, there is a very clear pattern- people who live in warmer areas have better MPG than people in colder ones. Summers are better than winters for people who live in places with actual seasons. Yes, the A/C can drop your FE, too, but honestly I don't think it's as much as running the heat plus warming up the engine. Also, if you care as much about MPG as a lot of us do, you try to minimize your A/C use to get better FE.

Personally, my experience has been as follows: I bought the car in the fall- had initially mediocre mpg, but I didn't know what I was doing, so as it got colder, my FE dropped and dropped. A few long road trips at high speeds killed my lifetime average. Winter was difficult, but as I picked up some techniques from my own trial and error and from advice on this forum, I started to get better and better mpg. Then mild temperatures dawned and my FE skyrocketed.

After spring ended, I expected that using the fan and A/C would drop me back to the wintry days. Instead, when we were hitting hot spells, 90+ days, I was breaking all my individual FE records, again and again. I'm working on my best tank ever, following on the heels of four tanks that were each personal bests at the time. The heat wave has started to diminish- and I'm worried my FE will take a hit.

My interpretation of this is that the HCH loves the heat. My engine warms up almost right away, but I've never had it come anywhere near overheating despite at least a few days of 100+ weather, and I may finish this tank at about 60 mpg (59.4 at the moment).

 

I thought the heat was killing my FE, which it was because I had the AC set to auto on 72. With 90-100 degree days, that caused the AC to run full blast. I find I don't take that much of a hit to FE if I set the temperature 5 degrees below the outside temp and slowly drop the temp to keep the fan running at very low speed.

Of course this only works effectively if you do not have people sweating in the back seat...

 

I am having the same kind of drop in mpg in the Phoenix area where its over 100 for months. The worst is when you are in a drive thru and then battery runs down, then you see them mpg dropping and you aren't going anywhere. At least I am still getting better mpg than with the SUV I traded in.

 

I've observed the same as several here - high temps without A/C actually improve things. Wtih A/C, it's a big hit. My best full tank was 70-75 degrees, warm but A/C not needed. Hit 52 MPG. Recently after a very hot spell here (90's), it was 44 (actually had to run the A/C on the way to work at 5:00 AM one day). Both runs were in August - 52 was last year, 44 this year. Almost the same weeks...

 

I'm having the same results with a MAJOR drop in FE. I've been going up and up in each of my tanks. With the 90 - 100 degree heat in Pennsylvania and the extreme humidity, I've had to run my AC. My battery seems to run out quicker as well. Not sure if it's head related or not. I'm down to 43 on this tank and fighting to go higher. Last tank I was up to 53!

I'm ready for fall!!

 

I find that the car works a bit better in heat (as long as the A/C is off). With temps around 96F and high humidity in Houston, TX, I can maintain mileage between 48-52mpg. All this as long as the A/C is off (which can be brutal). Otherwise with A/C, I'm looking at 44-48 mpg.