2008 Prius mpg drop in July in AZ

If it's only been 1 tank of fuel so far you may just need to see if it returns to what is normal for your car. It can be many things that effect the fuel efficiency of the Prius as is with all cars.

If no codes are showing up or no warning lights it makes it difficult to work out what the issue may be.

Things like HV battery health, new roads and driving style, plugs, oil level or even bad tank of fuel.

 

If your air conditioning has to work harder, that can affect your fuel economy as well.

 

Our Prius has lived in AZ most of it's life and gets around 42-45 mpg. Highways it gets 45+

 

could be your hybrid battery getting weaker, or just the 12v. have you checked the oil level? are the cooling fan and intake grille clean?
in the end, it might just be the heat. get it tinted, and use window shades when parked in the sun.

 

Three things:

You moved to a place that's hotter than h3ll and your driving routine is different from before.

Your AC is running MUCH more than before. The HV battery powers the AC so it drains at a MUCH higher rate than in Colorado. The gas engine has to run more often to charge the battery due to the AC drain.

A higher temp battery is less efficient and powerful; especially an older, weaker one.

 

I would also think the gas bladder is becoming more pliable in the heat and gradually allowing an increasing amount of fuel. Within another tank or so it will probably level off and your fuel mileage will increase into the 40s again.

 

I live in the Phoenix area and have two gen 2s. If you are taking short trips (10 min or less) around town, 35-40 is normal for the summer.

If you are taking longer trips (20 minutes or more), your mpgs may possibly concern me.

I drive about a 20-minute,17-mile commute with an average speed around 60mph.i usually get about 45 in the summer. On weekends when I'm usually just driving from store to store, I'm into the high 30s.

 

Do you have your A/C on auto or manual settings? I believe there's a sensor on the dashboard for handling (assisting?) the A/C during auto function. The sheer heat from the Sun + the windscreen induced green house effect might force your A/C to work way harder than it has to.

You might want to experiment with using your A/C on manual settings to see if this increases your MPG - I know it works for me; I never use A/C on Auto mode - even on very hot days (though a heatwave in London is nothing compared to "Roasting Arizona" ).


iPhone ?

 

Bisco asked about your 12V battery. I know when mine started to go bad in my 2008 the mpg dropped considerably. This is because the engine is commanded to run more often to maintain a state of charge in the 12V battery that is no longer obtainable. I suspect it has already been replaced at least once because their nominal life is 4-6 years. Better check it or have it load tested at a parts store.

 

It probably is both, but the HV battery rather than the 12 V battery. You may find once the heat returns to more mild temperatures, things will get back to normal, In the climate you have at the moment, short city stop and go will hit the MPG, particularly as the HV battery gets older. But more than likely, plenty more life left in it, so don't worry too much.

 

When we are in Las Vegas...our 2009 Prius will only get 38-40mpg with the AC running in 110 degree heat...One other thing...you mentioned a change of oil...make sure you only put 3.75 quarts in ...not 4, because an overfill will reduce your mileage, as well...an overfill will muck up the MAF sensor ,too...so keep it under the full mark on the dipstick...Ye ol prius doesnt like extreme heat nor extreme cold...like in indiana in winter...28-35mpg at -5 F cold

 

I regularly drive 2 2005 prius and the mileage varies on both. One with 190k miles consistently gets 50+ mpg, even in Vegas 110 degree heat. The other one with 110k miles will get low 40s. Still can't figure it out.