Curious MPG loss with AC on. 10mpg drop!

If the front window is being hit by sun, you are getting 400-500 watts of heat into the car. If you remove it via AC, you are going to need substantially more watts than that to remove it.

i like the japanese method from the other thread. but i do agree that the interior soaks up a lot of solar radiation. i would like to see a longer test keeping the thermometer in the car and watching what it does with the a/c on as you drive around, compared to not exchanging the air. didn't mazda have a solar ventilation fan at one time?

That's what us poor folk do.

The car cover idea would be great but it's more work and you are more likely to scratch the car. Then again it could provide protection from birds and door dings.

I use the window shield from the priuschat shop and it makes a very noticeable difference. It covers the entire windshield and even the little side windows.

those are great. if i had to park in the sun all day, i would use one as well.

Anybody know how much heat insulation the car roof has ?

yesterday, i drove about 50 miles in 102 degree high humididity weather with a/c on full blast manual. tank had about 300 miles on it. i started at 60 mpg and finished at 58.7.

^^ that is about 51 mpg for the 50 mile trip. Nice!

Once your overcome the initial cooling down stage it seems like the AC has less of an effect on mpg unless your are stuck in stop and go traffic.

Excellent mpg btw.

does make it seem like you're losing 10 mpg's tho...

I agree. Saying you got 60mpg sounds so much better than 58 mpg.

I 'm happy to get 55mpg with my commute. If it were not for that 1200 ft. elevation gains I could pull off 60mpg tanks more often.

Yesterday on a 160 mile road trip, starting with a full tank and consumption meter reset to zero, I observed the following;
Highway speeds varying between 75 and 65, depending on posted speed limits. Very little town driving, probably less than 15 miles, ambient temperature, varying between 95 and 108, cabin temperature set on automatic at 74, and cruise control used most of the time.

When I got home the mpg display in the mfd indicated 42.1 mpg. That figure is pretty typical for what I have seen in the 4+ years that I have owned the car.

I would ask you to try it again without the AC on but given the heatwave you are experiencing I don't want to be responsible for you having a heat stroke. lol

What I observer is that since the hot season came, my hybrid mode is not available most of the time now. I guess this is because the car sits most of the time in the sun and the batteries stay hot all the time.

Do you mean EV mode? If the traction battery is too hot then you may experience a loss of the ability to run in pure EV mode. Do you have a scangauge so you can observe battery temp?

Yes EV mode
I don't have a scangauge yet, but the batteries should be hot, because in the car is very hot.

Like they say here on PC, if you are uncomfortably hot then so is your battery.

Hi mlg779. Just wondering if your prius a Gen2 or a Gen3?

Also, did it come with an "EV button" as standard equipment?

that's a mountain around here and ours all fell into the sea a long time ago.

It's Gen III, and yes it has an "EV button".
This afternoon i left the car in the shade with the windows open, and also we had some overcast. The car had no problem going in the EV mode, so I'm sure the problem is excessive heat.