Large drop in MPG

Hi:

I read the initial article about what to expect for mpg. I have owned my Prius for 10 months and it has run very well for most of the 10 months. My first month of ownership was in August. August in Phoenix is still very hot, 100 -110 F degrees. I used to drive 90 miles round trip to work, my fuel mileage was between 45-48 mpg with the A/C on. In the Winter, the fuel mileage was between 48-51 mpg (in Phoenix) Recently, the fuel milage has gone to pieces in a hand basket. My mpg has gone from 45 to 34.5 over a few weeks period. I drive my 2005 Prius until the blinker blinks, add fuel, do the math and bingo caluclate my mpg.

What I have notice is that if it is a cool day in Phoenix, 75-85 degrees, I get much better mpg even with the A/C on. Once it gets hot, the engine is continously running. Even today, at the stop lights with the battery more than half full but not green, the engine was still running to charge it up. Basically, in the winter I can expect to get battery power assistance from 10 to at least 40 mph. Now in the heat, the battery power stops after 12 to 15 mph and all I see is the engine running to drive the front wheels and charging the battery on the display. FYI, I use Mobile One Synthetic 5-30, what the Dealer puts in for Synthetics. Furthermore, I have even had the dealer install the BioPro QX3 which they promoted as adding some mpg. I even added Chevron Full Fuel System Cleaner to see if it helps.

I am at a lost on the poor fuel mileage. If this continues and the Toyota dealer cannot help, I may need to sell it and get a Yari or Scion.

 

<div class='quotetop'>QUOTE(brandon @ Jun 6 2006, 06:16 AM) [snapback]266610[/snapback]</div>

Hi Brandon:

I don' trust the computer (MFD) on mpg. Several months back the computer displayed an average of 51 mpg. When I fuel it up and did the math (how many miles driven divided by how many gallons put in) I got a mpg of 41. Yesterday, when I filled up the computer displayed an average of 38.5 mpg.



<div class='quotetop'>QUOTE(seasalsa @ Jun 6 2006, 04:53 AM) [snapback]266572[/snapback]</div>

The car is running with A/C Auto and recirculation on. The temperature is set to 75. The tire pressure is whatever the Toyota Dealer mechanic set it at for the Goodyears.

 

<div class='quotetop'>QUOTE(Tideland Prius @ Jun 6 2006, 08:04 AM) [snapback]266681[/snapback]</div>

That is good to know. My calculations or the cars calculation (what ever is higher) still put the mpg at best at 41 mpg.

<div class='quotetop'>QUOTE(seasalsa @ Jun 6 2006, 09:13 AM) [snapback]266725[/snapback]</div>

That is a good point your bring up about tire pressure. The dealer will not put more than 35 psi on the tires because with the ever increasing heat in Phoenix, the pressure supposed increases significantly. Therefore, if I put in 42psi with the Goodyear tires (which are rated at 44 psi) wouldn't I damage my tires? I believe the manual recommends 32 to 35 psi. I may be wrong. In my Honda Oddssey with Run flats and tire sensors, I typically see a jump of 6-7 psi as I drive and the temperature gets hotter.

Thanks for the information.