Dash MPG different than Actual MPG different t

It's like a hit or miss. This is my latest. 352 miles on just 6 gallons. But by hand it's 58 MPG

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Hello, new poster here, I am having a similar problem as the OP with a used 2012 prius that we recently purchased. Im following the guideline that was posted in another thread. I am from Ontario, we use the metric system over here so I will just convert everything to make it easier for you guys to understand.

- Have you read This thread Yet?
No

- What fuel economy are you getting and how are you determining fuel economy? (trip computer or manual calculations)
trip calculator shows average 5.0 L/100km (47mpg), but at the pump we are getting 6.03 L/100 km (39.7 mpg)

- What fuel economy are you expecting and why?
Close to 50 mpg as possible, we drive like regular prius drivers, ie like grannys and expect better mileage

- What are the approximate outside air temps?
around 27 degrees celsius (80F) in the afternoons, dropping to 14C in the early mornings and late nights.

- How long are your trips?
40km per day (approx 27 miles)

How old is your 12v battery? What is the voltage reading of your 12v battery after sitting over night?
do not know, we just purchased the car from the dealer 2 weeks ago

Have you had your alignment checked? Any pulling or abnormal tire wear?
no we haven't, but don't see any abnormal wear

- 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?
40/60 city vs highway. We follow speed limit in the prius as much as possible with the prius, 60km/hr in city, 100 on the highway

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

- What are your tire pressures?
do not know, need to check

- Is your oil overfilled? (i.e. above the full mark on the dipstick)
do not know, need to check

- Make, model, year, engine and transmission of previous car? (e.g. 08 Civic 2.0L 4 cylinder, manual transmission) What did you actually get on the same trips/commute? (Please give us actual numbers, not EPA ratings.)
2007 mazda6 4 cylinder, manual transmission. Get around 28 mpg in summer, dropping to 24mpg in winter.

- What region/state are you in? (if you haven't set your location)
Toronto, Canada

- How are you trying to drive (e.g. trying to stay in electric only?) and how hard are you braking?
try to stay in EV driving as much as possible in the city. We brake pretty soft so that we get more regen.

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

- Are you "warming up" the ICE (internal combustion engine) by letting it idle after powering on?
no, the weather is warm outside now so we don't do it generally. In winter we let it idle a bit though.

- Are you driving using D or B mode?
always D mode, don't know what B does

- HVAC settings? Are you using the heater, AC, auto mode, etc.? If using auto, what temp is it set to?
AC mode cycle on and off, set at coldest temperature

- 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).
looks factory, will check

- 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?
we just got the car

 

Here is what jumps out to me from your posting:

Have you reset the trip meters since purchase, so that it is showing only your MPG history, uncontaminated by the previous drivers? Are you resetting these trip meters at each fuel refill?

At 4+ years old, this is a possible trouble point.

A tire pressure check is mandatory, that is a common troublespot.

Don't do this. EV has its purpose, but "as much as possible" is not it, in city or anywhere else. Get at least a couple tanks of regular driving to get a feel for this new car and a 'baseline' MPG, before trying to use EV or other hypermiling methods. Without this baseline, you can't tell if your technique is helping or hurting. It is very easy to use EV wrong and sabotage the MPG performance.

All EV energy ultimately comes from gasoline. In general, the less this energy is processed from mechanical to electrical to chemical and back again, the better.

This should not matter much. Aside from AC tuning, this mode choice is almost entirely a matter of user interface, not real engine control. While ECO will be best for the largest group of people, different people do better in different modes, and some people find no difference at all.

For best MPG, turn up the AC temperature and turn down the fan speed as far as is comfortable. Excess production of 'cold' just wastes fuel. Point all the vents into your own face, if you lack passengers.

How many miles - kilometers are on this car? If beyond very roughly 40k miles or 60k km, it likely has replacement tires. If so, we want to know the tire brand, model, and size. Many replacement tires are not LRR, or not LRR-enough, so will consume extra fuel. (This isn't all bad, they may also have better traction than the original tires.)

 

thanks for the reply. The first tank of gas, we pumped 35L and got around 604 km out of it, which translated to around 39mpg. Currently, on the 2nd tank of gas we reset the trip monitor and so far logged about 60km. The trip calculator is showing a DTE of 745km remaining without any major fluctuations like we saw while driving on the first tank. Could it be that, because the car was sitting on a lot for so long, it needed to recalibrate and that was the reason our initial poor fuel economy? I guess I will have to wait and see.

For your other points: I have taken your advice and lowered the AC and fan setting. I personally find the eco mode helpful; it may be my imagination but it feels like there is less power available and its harder to accelerate so quickly from a stop. You may be right about the tuning of the AC, it doesn't get nearly as cold as when I am in normal or sport mode. The car has 97,000 km on it approx., which is around 60k miles. I still have to check the brand and the condition of both the tires and the 12 V battery. I will keep you posted.

 

Eco mode lowers the throttle 'gain' at small to mid pedal positions, but if floored, you get full power in Eco mode.

Yes, Eco mode also cuts back the A/C power. I'd like to know how much difference the A/C really makes, but it would be hard to deyermine.

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Try turning AC off?

 

Don't count anything before the very first time YOU put gas into it, unless you ave personal knowledge that the tank was topped off and the trip meter reset at the same time, at the time you acquired the car.

If the trip meter was not at Zero when you started driving this car, then some of that tank was burned by someone else, with different driving conditions and habits, and an unknown number of MPG-busting engine warmup cycles. Even if someone zeroed the trip meter at purchase time, if the tank was not also topped off at that time, the fuel gauge could have appeared 'full' even with a gallon or so missing (from other test drives) , screwing up the MPG calculations at the next refill. For these reasons, we normally advise to ignore any MPG calculations for distance traveled before you personally fill the tank for the first time.

Don't read too much into the DTE display. It is just a forecast, assuming that the rest of this tank is driven under exactly the same conditions as the previous few hundreds or thousands of kms. But this is really a poor assumption, because differences in weather and traffic and road conditions and speeds and driver style cause considerably different fuel consumption rates. However, the car has nothing else on which to base this forecast.

Because of these uncertainties, the DTE estimate does set aside a reasonable margin or reserve, so reasonable drivers who don't look at DTE for an hour are unlikely to get the rude surprise of running dry when the earlier pattern would have suggested that fuel should still be present.

Because it is a crude forecast, and conditions are continually changing, don't expect DTE to consistently fall 1 unit (mile or km) for each 1 unit added to the trip meter. It just doesn't work that way. Forecasts change as newer data is added into the mix.

Technically, it is your imagination. Just press the gas pedal farther to get the power you want. The very same power is available in all modes (though ECO might have a slightly longer time delay, a good fraction of a second), but it happens at different pedal positions. All modes match up at both ends of the pedal travel, fully released and fully floored.

The tires are almost certainly replacements, nt factory originals. Battery could be either, and is not necessarily a problem yet if it is still original.