From 45 to 40 MPG ... What Gives?

Probably a failing 12v battery.

Many many posts on here about pour fuel economy due to the 12v battery starting to fail. The car is continuously trying to charge the 12v and as such uses more fuel in the process.

Am sure others will elaborate.

 

Answering at least some of the questions from http://priuschat.com/forums/gen-ii-...-answer-these-questions-esp-if-youre-new.html would help us.

In particular, I'd answer at least:
- What fuel economy are you getting and how are you determining fuel economy? (trip computer or manual calculations)
- Is your oil overfilled? (i.e. above the full mark on the dipstick)
- If reporting a mileage drop, did anything significant change on your car (e.g. accident, hit a curb or big pothole throwing off alignment, oil change/other maintenance/repairs, changed tires or wheels, etc.) or your commute?
- How old is your 12v battery? What is the voltage reading of your 12v battery after sitting over night? (Method Here)

I saw you posted about roof racks. Did you install it already? If so, that could add drag and reduce mileage.

 

Tire pressure?

 

Change in use of A/C? You're in Florida so that could be the culprit. I did an experiment last week and a half and used the A/C as little as I could and jumped back up from 44 to 49 here in Phoenix.

 

Increase the tire pressure until you don't like the ride or handling. I start at max sidewall pressure.

 

Most people that are interested in getting better mileage run tire pressure that is higher than the recommended pressure given by Toyota. You can find the Toyota recommended pressure (35 psi Front, 33 psi Rear) on the decal affixed to the driver door frame. In addition, people who run the recommended pressure have noted a wear pattern consistent with underinflation (edges wear faster than the center of the tires) Even with a higher pressure (40 psi front, 38 psi rear) I had more edge wear with the original GY Integrity tires.

I now run 44 psi Front (max sidewall pressure on tire) and 42 psi Rear with Michelin X-Radials and the ride is comparable to the GY tires at a slightly lower pressure.

Also, whatever pressure you run, tires usually lose a couple of psi over a month or two, so the tires can be underinflated if you haven't checked for a while. When I notice a drop in mpg, it is often for this reason.

Heavy A/C use will drop the mpg, especially when combined with stop and go driving and/or short trips. Freeway driving with A/C doesn't have as much of an effect on mpg, in my experience.

 

I had a similar issue sometime back. The culprit was the plastic shield under the front of the car was hanging slightly down (it had hit a parking curb and gotten torn). I fixed it and pulled it back taught... and that helped my mpg by a couple of miles...

I guess you have to keep the car's slip stream smooth... (front and back too - look for rear spoiler damage).

 

Clean your cabin air filter, engine oil should be 2/3rd's up the dipstick, cycle your emergency brake on and off a few times, change out your 12 volt battery for an Optima yellow top and fit kit, tyre pressure at 44 f 42 r, get anything out of the car that doesn't need to be there(weight)and last but not least...

My mileage was not great (51.3) but consistent, the engine felt like it was involved more than it should be, the other night from outside the car I pushed the start switch twice(powering up the car) to close the windows then pushed it once to turn off the car but must have missed and didn't see it wasn't off, next morning got in and... dead battery, hooked up a charger, took 30 seconds and the car started, don't know why but now the traction battery is more powerful, the ice is not as involved in around town driving and my mileage is pushing 55mpg...my theory is :cheer2: being basically a digital device, unplugging it periodically (just like a computer) starts it over with no weird ground anomalies