What am I doing wrong?

I have a 2010 Prius that I just purchased last November. I have notices in the past few months that the average amount of miles I get per tank has really decreased. I have gone from over 400 miles to around 370. I do lots of driving I already have 20K miles on my car. Any idea of what can be the cause of this? I do understand that the AC will have some effect but not this much.

You need to give us miles per gallon, not tank, since we have no idea how much you put in.

Also, fill out cwerdna's fine questionnaire by copying/pasting from here:
http://priuschat.com/forums/gen-iii...-answer-these-questions-esp-if-youre-new.html

Partial list of possible issues:

short commute
aggressive driving
AC
Low tire pressure
Overfilled oil (common at dealers and other oil change shops)
Use of wrong oil
Dying 12V battery
Clogged air filter (seems early unless you are in dust alot)
Fouled sensor (e.g., MAF)
Dragging brake
Bad spark plug

You get the idea, it is a long list so help us help you.

- What fuel economy are you expecting and why?

About 420 miles per tank. This is what I was getting when I first purchased the vehicle.

- What are the approximate outside air temps?
Its summer time in Southern California. The morning commute can be 70-80 and evening commute 90-100

- How long are your trips?

36 miles one way

How old is your 12v battery? What is the voltage reading of your 12v battery after sitting over night?

8 months old. I dont have all of that info yet.
Have you had your alignment checked? Any pulling or abnormal tire wear?

Not that I can really notice. I belive the alignment was checked at the 15,000 mile service.

- How much of it is city vs. highway? Roughly what's the average speed in overall and and of each segment? Is there a lot of stop and go driving?

Its hard to tell I'm in southern california traffic. Half the commute is stop and go and half is about 65-75 mph

- What's the terrain like of your drives? (e.g. flat, gentle hills, steep hills, etc.)

All of the above. LOL
- What are your tire pressures?

I'm not sure

- Is your oil overfilled? (i.e. above the full mark on the dipstick)

I"m using my Toyta care so what ever the dealer left it at.

- Make, model, year, engine and transmission of previous car? (e.g. 08 Honda Civic Si 2.0L 4 cylinder, manual transmission) What did you actually get on the same trips/commute? (Please give us actual numbers, not EPA ratings.)

I had a 2006 PT Cruiser. The MPG was horrible I was getting around 18
- What region/state are you in? (if you haven't set your location)

Southern California LA area.

- How are you trying to drive (e.g. trying to stay in electric only?) and how hard are you braking?

Lots of hard braking on the free way in the morning no way to avoid that.

- What modes are you using, if any? "normal", EV, power, eco?

Eco mode

- Are you "warming up" the ICE (internal combustion engine) by letting it idle after powering on?

No I did not think I had too.


- Are you driving using D or B mode?

D

- HVAC settings? Are you using the heater, AC, auto mode, etc.? If using auto, what temp is it set to?

AC is at 73

- Are you using the factory tires and wheels? If not, please indicate tire make, model and size (e.g. Goodyear Assurance Fuel Max 185/65R15).

All stock but I did take off the hub caps.

- 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?

Hit a curb and lots of pot holes. The roads here suck.

I think you answered your question there.

Right off the bat I would say check your tires with a good digital gauge. Run them a bit higher than 32lbs. Undoubtedly the dealer reset to 32 or less psi.

Also, there is a really good chance the dealer used the wrong oil (0W-20) and/or they overfilled it.

Thanks lets say they did over fill my oil. How would I fix that?

Check the oil level in the morning so all the oil has settled. Make sure you vehicle is on level ground. The oil level should not be above the full mark.

When I change my oil I only replace with 4 quarts even though the manual states capacity with oil filter is 4.4 quarts.

I change every 10,000 miles and nearly 4 quarts comes out. The oil level is usually about the middle, or slightly above, on the dip stick which is in the normal range for proper lubrication.

Next time bring 4quarts of oil with you, 0W20. Tell them thats is all you want them to fill the crackcase with...

hope this helps..

alfon

If overfilled, you can take it back to the offending shop, siphon some out, or drain some out the drain plug by almost removing the plug.

Also, try to think in terms of miles per gallon, rather than per tank, because your tank fills will vary, but a gallon is a gallon.

No doubt your mpg reduction is real, but we have no idea what you used to get or what you are getting now.

What I do is when I fill up I reset my odometer and compare to what the computer says I will get. I used to fill up and it would say 408-425. I would get over 400 miles to a tank. Now I get around 375 at most the computer says I should get around 380-400 even though I never get 400 any more.

I give up.
Good luck.

LOL thanks anyway man.

OK, what you're doing wrong is not tracking your mpg. You can do it two ways:
(1) Zero trip A each time you fill the tank. The trip A display will show you how many mpg you are getting averaged over that tank. The computer mpg will be high by about 5%, unfortunately.
(2) A more accurate way is to zero trip A when you fill the tank, read from trip A the number of miles you drove before you refill the tank, and divide that by the number of gallons you pumped (read from the pump) when you refill the tank. You need to fill the tank the same way each time, say to the first point where the nozzle shuts off.

Until you determine what mpg you are getting we have nothing to compare to what we normally measure: mpg.

(possible mechanical problem) Given that you are driving on rough or uneven road surfaces then there is no advantage to inflating your tires more than 5 psi over the the recommended settting printed on the inside of driver's door frame - however, having underinflated tires could lower your fuel efficiency by 3 mpg or more. If you've hit one too many potholes you could have a slow leak in one of your tires and have less air pressure in one of your tires OR the Prius wheel alignment could be messed up. Both could lower your MPGs. You may consider having an auto mechanic check out your Prius for you.

To get better fuel efficiency

1) On the 75-65 mph highway section - limit your top speed to 60-65 mph ( Driving slower should lower your use of hard braking on the freeway). If you can give yourself more time to drive - you wouldn't have to drive as fast. The Prius gets about 67 mpg using cruise control at about 50mph and it gets about 60 mpg using cruise control at about 60 mph. Even at 65 mph using cruise control for about 20 miles you should be getting about 54 mpg. Giving yourself more time to travel is a key factor in achieving higher fuel efficiency.

2) During long periods of stop and go traffic - the Prius HV battery can get depleted when the Prius is driven at a very low speed for an extended time period - if you are driving in stop and go traffic for more than 20 minutes, the Prius HV battery can get depleted and cause the ICE to go on automatically to recharge the HV battery pack (which is the least economical way of recharging the battery and cause your MPG to drop by as much as 5 mpg during the summer). So for extended stop and go traffic longer than 15 minutes = you should use a Pulse-and-Glide hypermiling technique rather depend on the electric motor. This means waiting until there is a significant distance(atleast one or three car length in front of you) before pressing the accelerator. When you press the accelerator make sure you quickly pass the middle of the HSI indicator (pass the ECO capsule but not too far to the right that you are in the power section, so the ICE is on) long enough so that you reach the top speed that you'll need (10-15 mph) then quickly ease off the accelerator so that you are not recharging the batteries but you still are still inside the left side edge of the ECO bar ( ICE is off and electric motor is at min power) and allow the Prius to glide (the glide distance for a flat surface should be about 1/2 the distance you need to cover) until you need to hit the brakes to stop the car.

3) Raise your AC from 73 to 78.

4) Avoid E15 gasoline- while preliminary reports say the 2010 Prius can run with 15% ethanol mixed in with gasoline - it will cause your MPG to drop.


HTH

Walter Lee
2010 Toyota Prius III, Blue Ribbon/Dark Grey, oem floormats
Yokohama Avid S33 (front 50 psi/ rear 48 psi)
ScangaugeII ( AVG/Fwt, Soc, GPH, RPM)
Washington DC/MD/NoVa
Odeometer 15300 miles - 60 mpg overall
Last tank = 10.18 gallons E10 87 oct/ 695 miles (68 mpg)

i think your tank may be shrinking with the warm weather. it will expand again this winter. these new vegetable based materials are unstable.

Go 60-65 MPH on a SoCal freeway? Hahaha. May be the funniest thing I read all day.
I think it's almost impossible to get these 60mpg's I've been reading about in LA. Surface streets have a light at least every 1/4 mile and you seriously can't go under 65 on the freeway or you'll kill someone. (Then again, most of the time it's bumper to bumper stop and go- another MPG killer) That being said- on my 3rd tank of gas and I'm getting 47MPG on the read out. My best was 51 from LA to San Diego- no traffic cruise control on 70- as I was in the right lane being passed by everyone.

It's been pretty hot down there so I'm going to guess your AC is working harder than it was when you got the car and into early summer. Your commute is not long enough to overcome the initial large hit to mpg. Combine that with setting the AC temp so low and you could experience a decent drop in mpg.

Buy a windshield shade, park under a tree and set your AC to 78° or higher and see how the next few tanks work out.

I don't understand why the Australian manual recommends 36/35 psi and the US recommends 32psi? Psi is Psi in both countrys.

Toyota USA values comfort, whilst Toyota AUS values handling?

Comments:
The Prius Gen III (my 2010 and up) does not have a fuel bladder the way the earlier models. So, there is no cold/hot variation in the amount of fuel the tank will hold.
Recommended tire pressure is NOT "32 PSI." For a 15" tire, it is 35 PSI front, 33 PSI rear. If you have 17" tires, the values may be different.

Suggestions:
1) Raise your tire pressures to 40 PSI front and 38 PSI rear - the higher PSI will reduce the rolling resistance.
2)Hitting the pothole may have affected you alignment, which will impact the MPG. Get the dealer to check.
3) Keep your highway speed to around 65 MPH. At 70 MPH the MPG drops.

Review the suggestions that Walter Lee posted (above).
Also, I would suggest that you change the TRIP display screen to show MPG and get off this silly "miles per tank" nonsense. Your fuel gauge may be fooling you about the state of the tank.