prius just dropped mpg....what the?

Although you're stretching the truth here with the 140 figure, I think these peak summer temps have a lot to do with it. This is my first summer with a hybrid and have notice a remarkable drop in FE in just the past couple of weeks. Short trips doom you too.

Remember, the A/C also keeps the hybrid battery cool.

 

When you refill your tank do you press the reset button on the MFD, or do you just let it reset itself? If you don't press the reset the MPG gets averaged over multiple tanks instead of the current tank. You could be seeing some of you trip MPG in your current reading.

 

I agree. I am dealing with the exact same conditions now that the temps here in San Antonio and Houston are > 100F. I am lucky to get 40MPG even with the Enginer kit on. My car is the same year and approximate mileage as the OP. When the temps get back down to ~ 90F, my mileage increases by 10MPG. At 80F and below, I can pull 65MPG.

There is a fan mod available.

Prius OEM fan control - EAA-PHEV

 

I'd agree with those who have mentioned this as the most likely culprit. The temperature and amount of sun is probably significantly higher now than it was prior to your trip. The A/C is working harder to keep the car cool. Not sure if you are driving more 10mile trips and less 40 mile trips than before, but if so that would also amplify the effects of the A/C. If there is any sort of slow leak in the A/C system that would reduce it's efficiency and make it even worse.

 

I've taken to setting my A/C at 80 degrees (it's not as hot here, but quite a bit more humid) and once it gets to that temp, slowly lowering it to what I find to be comfortable. You'd be surprised how much higher you could set it and be OK, granted everyone has a different temp comfort zone.

Does your A/C ever get to a lower fan speed when it's running? Have you thought of tinting your windows? I found that makes a BIG difference in perceived temperature out here, and helps the A/C not have to run as hard to keep the temperature cool in the car.

 

Nah, it takes quite a bit of energy to pump heat out of a hot car into the hot outdoors. Any car would suffer reduced efficiency with the A/C on, not just hybrids. For that matter the Prius A/C is more efficient than a lot of other cars because of its variable speed compressor.

It is possible that whatever is making the noise might also be contributing. I didn't understand exactly where you said the noise was coming from.

 

I am in MS, so 'high' is about 105, but the under hood intake air temp spike above 90 so I see intake temps of 130. I bet a scan gauge would show 150 in the intake air in Phoenix.

My MPG is 40 in winter, 47 in spring and fall and 42 in summer.

 

The nice thing about the Scanguage is that you can take readings for the traction battery high and low temps. Once you exceed (I forget the exact value....140F?), the system limits the use of EV boost and MPG takes a beating- hence the fan mod. I've built it for mine but haven't had the time to install it yet. Word has it that it is an essential upgrade for hot climates like Az.

 

You're correct 05az. The 2004 2005 and I think 2006 models automatically reset the MPG calculations each time you fill the tank.

Re the battery cooling fan. It's a pretty easy job to remove the right side panel in the rear hatch to access the fan for cleaning. It does tend to get pretty clogged up (with dog hair for example if the previous owners had a dog). Mine worked much more efficiently after I cleaned my clogged up fan. Also make sure the vent near the rear seat isn't obstructed by anything you're carrying in the back.

See my pictures here : http://priuschat.com/forums/gen-ii-...ur-dirt-causing-major-battery-problems-4.html

BTW. Please read the information on your tire sidewall and post the exact brand model and size. Yes I know it might not explain the observed drop in MPG but it does help us understand what MPG you can expect to get from the car.