Milege low on 2014 Prius

If that was the first time you filled it, it doesn't count because the dealer's previous fill most certainly did not top it off the same way you did.

 

Thanks, spiff72. When someone mentioned the fuel level sensor, I wondered the same thing, unless it's something like a thermometer and measures along a continuous line. If there was a flow rate sensor, one would hope it'd be more accurate than what we seem to be seeing in the CONS display. I agree you're 3rd item is more likely, but I'd like to see something to explain it a bit, even in simplistic layman terms. I don't believe Toyota fudges, any more than the EPA estimates are intentionally fudged, but I wouldn't be surprised. And, come to think if it, maybe the CONS uses the same formula.

 

In the summer of 2009, I drove to Madison WI with different sized tires on the front and rear. On Sunday morning, I swapped the tires front-and-back to drive back:

• Sumitomo 175/70TR14 - 886 revs/mile, 1.8% slower than stock
• Sumitomo 195/70TR14 - 849 revs/mile, 6% slower than stock

With the 175/70TR14 on the front, the odometer, mile markers and GPS agreed on both speed and distance. With the 195/70TR14s, the odometer, mile markers and GPS were off by 6% giving a lower indicated speed and distance. Since I do regular testing of full tanks including running them dry, the pump calculated MPG matches the 6% offset from the oversized tires.

So I am quite content to use the following calculation:

• actual_fuel_burned = indicated_miles / indicated_MPG

Bob Wilson

 

First and foremost, just about every answer in this string does have merit, so read each one carefully and glean as much information as you can. With that said I am going to share what I have learned on this subject since I started driving a Prius. As shown in my signature file below this is the second Prius I have driven and the first one that I have personally owned. #1 was my wifes...

• Don't believe the stuff the dealers will tell you. Most of them on the sales floor don't have a clue. They only sell cars. There are exceptions to this rule, but for the most part you will find it is true.
• Concerning air pressure, look at the "maximum" pressure that is plainly marked on your tires that are mounted on your car. You can safely inflate your tires to that setting when the tires are cold. Cold is defined as being at the same temperature as the ambient temperature that surrounds the vehicle. The engineers who designs your tires has made all the calculations as far as load, speed, and other factors for maximum air pressure. It is best to set the air pressure in your tires the first thing in the morning before your car is driven. It is also a good idea to not have any source of radiant heat being subjected to your tires. This includes bright sunshine. Again, set your pressure early in the morning before you drive your car. On the Prius, standard stock size tires (15") should be maintained with the pressure two (2) pounds higher in the front than in the rear. If you are running low profile (17") tires you should maintain one (1) pound higher in the front versus the rear. The absolute minimum of pressure allowed in your tires should be the placard setting that is found on the driver's door jam. I suggest you start at the placard setting and then increase the pressure every so often until you are comfortable with the way your Prius handles. Do not exceed the maximum pressure that is stamped on the sidewall of your tires. Once you find the pressure you like at that point you simply need to maintain said pressure. Simply check your tires, and adjust pressure as needed to maintain your preferred pressure setting at least once a month. When doing so, also take the time to inspect the tread, the sidewalls of your tires, and also look for any foreign objects in your tires such as nails, screws, and anything else that might puncture the tire. If necessary have your tire repaired and or replaced if needed if you find a problem. It is a good idea to have a tire shop remove any foreign object rather than yourself. This will lessen the chance of your tire losing air pressure and having a flat tire. It is also a good idea to rotate your tires every 5000 miles and also keep the tires well balanced. These two things will help to give you a better driving experience as well as lengthen the life of your tires and the suspension parts of your Prius. It is also suggested that you keep your front end aligned properly. Some folks even opt out for a four wheel alignment. This can be done by using aftermarket shims. Some good alignment shops can do this sort of work for you. Normally the rear end will be okay. But over time, you may find you will need to make some sort of an adjustment there.
• When filling up the Prius. I suggest you fill slowly using the auto fill on the pump. When the pump clicks off hang up the nozzle. It is NOT a good idea to top off the fuel tank. When doing so you risk damaging expensive parts of your pollution control system which includes the carbon canister and other devices on your Prius. I also suggest you run top tier fuels. It is a waste to run any thing other than 87 octane (regular) fuel. In mountainous areas it is okay to use 85 octane rating. This applies in the USA. Other countries have their own system of octane rating. Refer to the owners manual for more information.
• Finally when calculating MPG on your Prius, you will have the best luck if you get yourself a fuelly account and track your mileage there. Another alternative would be to run an Excel spreadsheet or something similar. Checking MPG on a single tank really does not tell the whole story.

Best of luck to you. I hope you enjoy the experience of driving and owning a Prius. IMO the Prius is the best mid size five (5) door hatchback out there today.

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Ron (dorunron)

 

I can't give you any documentation, just 10 years of driving 3 different Prius models over 10 years.

The 5 minute and 1 minute (and instantaneous) consumption gauges seem to use a flow rate consistently. However, the Trip A and Trip B consumption gauges do not have a consistent calculation from model year to model year.

The 2002 and 2010 I've driven most seemed to have Trip A and Trip B consumption gauges that were flow based but the 2014 I've had for a week does not. My 2014 shows consumption of 40.7 mpg currently, yet every trip I've taken - including a 55-minute trip where all but 1 5-minute increment registered over 75 mpg- seems to make very little difference with the Trip A or Trip B gauge. When I shut the 2014 off, I get a readout of the mpg from power on to power off and EVERY ONE OF THEM was over 50 mpg, yet the Trip A gauge started at 18 mpg, then crept to 20 something , then 22 something, etc. It's a slow build but the consumption rate shown isn't close to the realized rate I'm getting. I usually re-set Trip A after every fill and leave Trip B alone, so I'll get a better feel after a few thousand miles. But I think Trip A and Trip B are using a different calculation in the 2014 than I have seen in my earlier models.

Hope this helps.

 

its my 1st time to own a prius 2014, the best mpg i had was 60 and my bf did 70.. can't complain, i used to have 30-40 on my HC

would it calculate the mpg better if i use the fuel log app from the phone?

 

The short answer is "to some degree". The only way to get accurate mpg is to top off the fuel consistently and that is not practical and can damage some parts of the system, so IMHO you don't really want to do that. However, after the first fill-up, you can start to get fairly accurate mpg by using the slow setting on the pump and stopping when it shuts off. Then you simply divide the miles driven by the amount of fuel pumped. It will never actually "fill" the tank all the way, but if you fill the same way consistently, it's about as accurate as the average driver can get. I like to use Slow because it seems to vary less station to station whereas some Fast really are "fast". There will still be variances between pumps, etc., but after several fill-ups, it'll begin to average out.

The app on the phone will simply do the math for you when you enter the miles and amount. It'll also keep a record for future reference and if you use an app like Fuelly, it'll keep an online record and add to the database of user experiences.

The computer in the car calculates the mpg based on factors that so far haven't been documented, at least that I've seen. Some speculate the results are skewed on the high side to make owners "feel better". Others speculate it is more accurate because it takes all the pump variances, etc., out of the equation. Every once in a while I topped off my old van for 2 fill-ups to see how accurate my average and the computer average in it was. I found the minor variance just wasn't worth fiddling with the pump handle, risking spilling gas all over the side, etc. Many of us record both what the computer says and what we compute when we fill-up.

And don't forget, the Prius has so many variables that affect mpg, that comparing them to what others get is kind of pointless, way more so than traditional cars. Heck, even headwinds and tailwinds can make big differences, as can traffic patterns, etc. IMHO, the only valid use of mpg stats is to see when a problem might be developing or how a change you made with new tires, different air pressure, etc., has affected your mpg. Watching the mpg over time can also indicate whether or not a change in driving habits is more efficient.

 

You can get reasonably accurate calculation, tank-by-tank, by just stopping when the pump (any pump) shuts off. The errors due to idiosyncrasies of various pumps are very minor, barring a failure of the shut-off mechanism.

Any calculated mpg error on the first fillup will be, for all practical purposes, be completely eliminated on the second.

 

Yes, you can, that's why I said "accurate", not "reasonably accurate", and certainly didn't expect any blowback. Had I said "reasonably accurate", someone would have jumped in saying something about accuracy. This forum is loaded with questions/comments about mpg, so it's obvious many are not satisfied with the reasonably accurate data you and I are. I might just use Toyota's number because it seems to always be higher.

And, I've got a "lot" of experience topping off with a variety of pumps and stations around the country over the 16 years I owned my van and there is a lot of variance between first shut-off and "full", which means there is a lot of variance between empty and first shut-off. And a lot of it has to do with those rubber covers over the nozzle. As I said in another post, 1/2 gallon makes about a 2.5 mpg difference with the 11.9 gallon tank in the Prius, only about .5 mpg with the 26 gallon tank in my van, that's why I said after "several" fill-ups, especially if you don't use the same station mostly times. I completely agree with the reasonably accurate mpg I get using the first shut-off technique, I was just trying to provide a more complete explanation of some of the variables.

 

DAZ said

And this is very accurate indeed. In fact, as the tanks accumulate the accuracy continues to improve.

As Mendel said, a calculation using two successive tank fill-ups is going to satisfy all but the most OCD amongst us. My guess of the two tank maximum error is about 50 ml / 20 gallons, = 50/20*3.8*1000 = 0.00066. At that point the pump meter introduces more error.

Off hand I'll guess that people who are intuitively suspicious of the hand calculation recognize that precision is poor but do not realize that cumulative accuracy is excellent.

 

I got to thinking about the "first fill-up" comments I've made here and in other threads and I suspect I erred. Chances are the dealer stopped filling at the first shut-off too, so if you do the same, the mpg should be relatively accurate from the very beginning.

 

I would just ignore that first tank, especially if the car did a few demo drives. Dealerships tend to "warm it up for you" and all sorts of gas burning horror stories.

 

At least where I have bought cars the dealership fills the tank as part of the customer delivery checklist.

 

I plan to, just wanted to back off my statement whereby I implied the dealer topped it off. I'm also ignoring mine because I spent an inordinate amount of time running the A/C (and ICE) without moving while I was playing with controls, audio and navigation.

 

Next question -- which no-one outside the dealership can actually answer -- did they really re-fill it as part of pre-delivery? Or could it have been filled earlier before test drives and demos, and then the pre-delivery tech glanced at the gauge and found 10 bars, so felt that no additional re-topping was necessary?

Neither of my Prii had the full pre-delivery checklist performed. Both were delivered with tire pressures of 40-ish psi, the factory setting for the Pacific delivery cruise. Pressure is supposed to be reduced to the door placard levels as part of pre-delivery.

I didn't complain, and even use it as evidence that 40-ish psi is acceptable even to Toyota, or at least to its PNW dealers.

 

Check the spare psi too. Ours was around 40. It's a pain (per most), you gave to get it out to check.

 

Thanks for the reminder. I want to take mine out before our trip at the end of the month just so I know how.

 

Yeah, try out the scissor jack too. It works, but it's a pretty poor design. The linkage between the cranking part at it's counterpart on the jack is smallish, which means with each crank it's sort of fighting. It looks chewed up real quick. Try cranking up a (worst case) front wheel. I'd suggest to throw into the underfloor tray:

* a small piece of plywood (to spread the load if you have to put the jack on soft ground)
* a lightweight pair of wheel chocks (owners manual shows to chock the kitty-corner wheel)
* some sort of orange/retroflective cone or triangle
* rags

 

Running a couple of pounds over is fine but too much actually "pooches" out the sidewalks. Radial tires, unlike the old bias plies, do not "stretch" beyond a certain point. Too much air and the sidewalls push outwards and can lift the center of the tire away from the road. Perfect conditions for hydro planeing. Makes for a nice little river of water running under the center. The higher the load range, the stiffer the sidewalls, but the effect is still there.

I have seen many Prius sized, front wheel drive cars with 80k-100k on OEM rear tires when they are NOT rotated. Most of the stopping force and all of the drive is on the front wheels. The rear just rolls. My Corolla has 84k on it and I just had the rear OEM tires replaced when the front ones came due. The OEM's on the front went about 30k and the next set went about 54k. I saved 10.4 rotations at 5k for 20 bucks a rotation. Sure, the front will wear out a little sooner but you have already paid for 2 tires just in rotation cost, plus you shell out for 4 tires (effectively 6 when you factor in rotation cost) instead of just 2 at a time. There is a lot of "voodoo" about rotating tires. Cross rotation is fine for radials. The front to back myth came out when Firestone 500's were seperating left and right back in the late 70's and early 80's. I saw my share of torn to pieces fiberglass on Corvettes as the "500" was its OEM tire until they got recalled and replaced by the Firestone 721 (which also got recalled I think).
Just $.02 worth of info from a former Goodyear employee.

 

OP's dealer is an idiot re: MPG, but I agree that best practice is to stop filling the tank on the first click. It is a poor idea to risk a spill into the evap canister or on to the ground.

I rotate my tyres every 10k miles at the same time I change oil. Cost: nothing. Time: zero
Tread life and wear pattern has been excellent by keeping them inflated at sidewall max recommended.