Completed Fuel Economy Questionnaire

You can't go by just one fuel up. I have never found that much of a disparity from the gauge mpg to actual. I think 3 mpgs is the biggest disparity I've ever seen. Here's a couple things for you though.
1) What is the psi on your tires? Air them up to 2 psi below max sidewall
2) You say you keep the AC fan on low but, what's the temp set at? If the temp is at max low, the compressor will work all the time causing excessive drain on the HV battery and in turn affecting your fuel economy. I recommend setting it on AC auto and setting the temp to 78 or so. I find this a reasonable compromise temp (not too hot, not too taxing on the compressor).
3) When you get up to cruising speed, do you take your time or do you go straight to the speed and hold? The latter is better
4) You need to make sure the car is in S4 (read attachment). If its in any other mode, you will not get the best fuel economy.
5) You also appear to have the Touring model which is known to get less fuel economy than the standard model (but only by about 3mpgs).

 

You have a North American Gen 2, which included a flexible bladder to reduce vaporization of the fuel. The flexibility of this bladder varies wildly. In MS I had fill ups between 8 and 11 gallons, but folks from near Canada have reported much smaller fillups yet. This variability will not impact fuelly over enough time, but plays heck with single tank results. (I found the onboard MPG to only be about 1% over fuelly over time)

I will give you my Gen 2 fill up mantra:
If your Mother in Law is in the car, get gas at 3 pips, she will never quit telling EVERYONE how you stranded her.
If your spouse is in the car, get gas at 2 pips, they will never let YOU live it down.
If you are alone, you can get gas at one pip, walking to gas station builds character. (Gen2 needs 3 gallons before you even try to restart)
If the last pip ever starts blinking, get gas NOW. I had it run dry in 7 miles. (I also had it NOT run dry in 30. You just can't tell)

Do not try to drive on just battery power.

 

11.2 volts is way low for a 12 volt battery, you should plan on replacing it soon. In some failure modes, the 12 battery can be a significant MPG drain.

 

if your computer is reading 49.6, you're getting at least 45 and probably a little more. follow some of the above advice and you'll be over 50. all the best!

 

optima is a good one. so is the oem from the dealer. exide makes one, check with local retailers like pep boys and auto zone. and get some good low rolling resistance tyres like michelin energy.

 

how many miles on betsy?

 

Optima DS46B24R Optima battery direct fit replacement for Prius 2004 + , Prius V & Plug-in Prius with Instructions complete step by step instructions included.
Exide AGM Car Battery (Group S46B24R)
Super Start® Platinum PRIUS - Battery | O'Reilly Auto Parts

 

Did you fill it up yourself when you bought it, or did the seller just say it was filled? If the later, then you don't really know if it was truly filled up, so don't count any miles before you personally filled it.

Please find out. Underinflation will cause significant MPG loss, though shouldn't explain your entire shortfall.

 

Greetings jharper03,

Like others said, pump the tires up. Try to run them at the maximum pressure stamped on the sidewall. Make certain the front tires have two pounds more than the back tires. If the ride is too rough, drop the pressure in two pound increments until you are comfortable. Set the A/C at 76 or 78 AUTO, NOT on LOW and fan speed low. If you are in a real hot area, 74 might be more comfortable when the sun is blazing. LO Setting, that alone is really dragging down the MPG (the A/C that is) as the compressor is running full speed at all times. Runs on electricity which is generated by the ICE and regeneration from braking. Use a good solar shade on the windshield when you are parked. Will help to keep cabin cooler, which in turn will make A/C work better with less energy. Make sure the tires are LRR (Low Rolling Resistance). If they are not, when the tires are worn out, get good LRR type tires. Your short trips are not helping you. As other's stated, Touring model's get about 3 MPG less than non touring. That 12 volt battery is toast. Get a new one. I recommend the one Toyota sells. Follow the instructions in the link in my signature below to change the battery. Dealer charges about $200 for the battery and anywhere from $75 to $150 to change the battery. You can DIY in one hour or less with a small handful of tools. Bladder has already been mentioned. You have to go by several tanks in order to get a real average on the Prius. When you see crazy numbers like you did, the next tank will probably be reversed in numbers and then it should settle down for a few tanks. That is the bladder for you. Saw the same thing on our Gen II. Learned real fast one tank figures don't cut it. Keep venting like you are doing, and fill at the slowest rate. DO NOT top off. Try to use high tier gas (Shell, Mobil, Texaco, Exxon, etc.) 87 octane is all you need. If you are not running synthetic oil, you should consider it. I recommend Mobil 1 5W30 for your Gen II. Keep an eye on the oil level. Check regularly. Lots of stories here on PC about older Pri using oil. Once it gets below the bottom dot, you will damage the ICE. Top dot to bottom dot is 1.6 quarts. At 3.9 quart oil capacity, at bottom dot you have less than 2.5 quarts in the ICE. So, like I said CHECK THE OIL REGULARLY. Make sure the air filter is clean and that the throttle body is clean also. Check and or replace the Cabin Filter also. Will help the A/C to work better. (Less Energy Again) Check both coolant loops. If one is low, top off and bleed air if necessary from the loop. Use only Toyota SLLC in the coolant loops. You might consider trying to determine if the spark plugs were ever changed, and if the coolant was drained at 100K. If not, both items should be done. I know I covered more bases than just the normal stuff that pertains to the questionnaire but you may have other issues that need to be addressed.

On the 12 volt battery. Be aware that the battery is a AGM type battery with special JIS posts. It is also equipped with a vent tube. Use the correct battery when replacing. You won't find this battery at WalMart. A fully charged AGM type battery should measure 12.9 to 13.1 volts with NO load.

Please update your profile with your location. It helps when answering questions about your Prius. Especially if you are in the UK or elsewhere. Different regions of the world have different stuff on the Prius. It does affect how the answers should be in certain questions.

Finally welcome to Prius Chat. There is a wealth of information here and some great folks that are ready to help you get the best out of your new to you Prius. Congrats on buying the best hybrid out there in my opinion.

Peace,
Ron (dorunron)

 

Yeah, just keep plotting the tank fill calculated MPG in Fuelly. You'll probably see the graph bounce up and down a lot (due to the inconsistency of the fill volumes), but after a while the trend line will be clear, and will give you a very good estimate of your true MPG.

BTW. Over a single tank, the computer displayed MPG is usually more accurate than a manual "gas pump" calculation. Over time however, the plotted trend line will give you the most accurate figure.