Can toyota modify MFD mileage calcs?

HybridVigor · 11-13-2005, 11:50 AM

I had an interesting experience when I took my '05 into Toyota for its "Yellow Service" / 5000-mile oil change combo. I requested that they use Mobil-1 Synthetic for the new oil. In the next couple of days after getting it back, I noticed that my MFD mileage estimates were consistantly lower than before the service. Initially I discovered that they had lowered my tire pressures from 42/40 to around 32-35 psi. (OK. No big surprise, although I would have like to be informed of the change) However even after that, the MFD mileage estimates remained lower than before, most notably at speeds at or above 55 mph where the "instantaneous" estimate has been 5-10 mpg lower.

I've since refilled the tank, and found that my overall mileage has not significantly changed. I'm still getting the same "real" mileage that I was getting before, but the MFD is now reading lower.

Is it possible that the dealer made a software update, or something similar, that is causing the MFD mileage to be calculated lower? Ironically, prior to the service, my MFD tank mileages were consistantly 2-4 mpg higher than the "real mileage" as calculated by gallons pumped/miles driven. After the service, they now agree fairly closely.

One parameter change that may complicate this is that the air temperature in my area (Phoenix) has dropped from 90 to 70 during the interim time period, perhaps altering the bladder rigidity?

Jaguar88 · 11-13-2005, 12:04 PM

Check the oil, its been reported that an overfill reduces milage.

HybridVigor · 11-13-2005, 12:14 PM

Quote:

Originally posted by Jaguar88@Nov 13 2005, 10:04 AM
Check the oil, its been reported that an overfill reduces milage.

[snapback]155006[/snapback]

Sorry, I should have identified that I checked for that in my first post. I did check, and they did overfill it in the sense that they filled it to the F-mark. I syphoned oil out through the dipstick pipe until the oil level reached the "ideal point" at 1/4-inch below the F-mark. I did that within two days of the service. Additionally, my overall mileage has not been affected as it would with overfilled oil. Good point, but already accounted for. Any other ideas on whether Toyota could have perhaps updated the software/OS to modify or "correct" the MFD fuel-efficiency calculations?

galaxee · 11-13-2005, 01:32 PM

did they rotate tires? may be secondary tire break-in.

DaveinOlyWA · 11-13-2005, 01:53 PM

its the temp change. 20º is more than enough to change a few miles or so. one thing i found it that the hotter it is, the better the mileage if all else is equal. usually most, especially people in your area, wouldnt notice because the air would negate any major differences.

keep in mind that if your commute is long, the difference wont be as much, since temps are only going to affect the first 5 mins of driving.

i drive an 8.8 mile commute. this past summer i would drive in the morning and lose +/- .1-.2 mpg on my tank. in the evening, i would gain .2-.3 mpg. no elevation changes to speak of, only difference was that my car in the evening would still be very warm from the heat of the day. (i got off work at 7-8 pm...sun doesnt set till 9-10 pm) didnt use air 90% of the time because i prefered the down window thing. (commute speeds never exceed 40 mph) so even with the loss of aerodynamics from the down windows, my mileage still improved.

so yes, temp plays a huge roll... in some cases.

HybridVigor · 11-13-2005, 02:01 PM

Quote:

Originally posted by DaveinOlyWA@Nov 13 2005, 11:53 AM
its the temp change. 20º is more than enough to change a few miles or so. one thing i found it that the hotter it is, the better the mileage if all else is equal. usually most, especially people in your area, wouldnt notice because the air would negate any major differences.

[snapback]155038[/snapback]

So why would my MFD mileage be affected, but my calculated mileage remain the same? Nothing has changed in my driving, same commute, same general hours. I agree that the colder temps lower mileage, but then why aren't both forms of mileage equally affected?

To perhaps answer my own question, maybe I'm just noticing the mileage change more on the highway because the cooler temperatures more dramatically affect highway mileage. Perhaps the faster air flow wicking temperature off the engine causes the instantaneous mileage to be noticeably affected, but over the course of a tank, there is more 30-40 mph driving and the effect is mitigated? I concede that the instantaneous MFD mileage does not appear to be dramatically different than I remember it being prior to servicing as long as my speeds are <40 mph. Maybe you've hit on it since the service did seem to match well with a rapid temperature change. Incentive to drive more surface streets during the "winter" for me?

Maytrix · 11-13-2005, 02:03 PM

Hey Gang,

I think everyone has missed the point. His actual calculated mileage has NOT changed. Just the readout on the MFD. IF he had 50mpg on the MFD on most fill ups prior to service, it sounds like it's now reading 47 or something lower.

Eitherway, it sounds like whatever caused the change, has just helped since it's made your MFD more reliable.

HybridVigor · 11-13-2005, 02:15 PM

Quote:

Originally posted by Maytrix@Nov 13 2005, 12:03 PM
Hey Gang,

I think everyone has missed the point. His actual calculated mileage has NOT changed. Just the readout on the MFD. IF he had 50mpg on the MFD on most fill ups prior to service, it sounds like it's now reading 47 or something lower.

Eitherway, it sounds like whatever caused the change, has just helped since it's made your MFD more reliable.

[snapback]155043[/snapback]

True on both points, Maytrix.

DaveinOlyWA · 11-13-2005, 02:34 PM

i understand what he is saying and i went through the same thing last year. another thing you might want to look at is the mileage you now have. when i first got my Prius, the MFD was consistantly 1-2 mpg higher on the average. as time went by, the difference became smaller. the bladder stretching a little bit would cause this right? so i accepted this.

but then right at this time last year, same mileage (well actually about 8,000 on mine) boom, the difference bet the two readings started to shrink and that can only partially be due to the bladder's not expanding anymore. so then you look at other changing factors and temp was the only measurable variable that i could see also...

now is this conclusive? after another year, the difference is now that my tank mileage has swapped places with the MFD mileage but the change has slowed considerably. but will have to wait out another winter to see what trends develope... too early yet.

the other thing i can say to this...if this aint the right answer then you need to

DUMP YOUR DEALER!!

if he is performing maintainence behind your back, get out while you can'!! i dont care what the procedure is or how critical it is. if someone does something to my car without telling me about it first, it will be for the last time

also, i really think you simply need more data before any real conclusions can be made.

jbarnhart · 11-13-2005, 02:51 PM

It stands to reason that there are coefficients in the onboard computer that will affect the accuracy of the MFD milage calculation. The Prius is offered with several different tire combinations in other geographies, for example. The MFD milage calculation needs to know the outer diameter of the tire for its distance calculation, so an incorrect setting would cause errors in the reported milage. There could be other internal settings which also affect this number. Sounds like the dealer may have caught an error and fixed it.

11-13-2005, 11:50 AM	#1
HybridVigor Join Date: Jul 2005 Location: Chandler, AZ Posts: 96 My Car: Model: Package: Thanks: 0 Thanked 0 Times in 0 Posts Friends: 0	I had an interesting experience when I took my '05 into Toyota for its "Yellow Service" / 5000-mile oil change combo. I requested that they use Mobil-1 Synthetic for the new oil. In the next couple of days after getting it back, I noticed that my MFD mileage estimates were consistantly lower than before the service. Initially I discovered that they had lowered my tire pressures from 42/40 to around 32-35 psi. (OK. No big surprise, although I would have like to be informed of the change) However even after that, the MFD mileage estimates remained lower than before, most notably at speeds at or above 55 mph where the "instantaneous" estimate has been 5-10 mpg lower. I've since refilled the tank, and found that my overall mileage has not significantly changed. I'm still getting the same "real" mileage that I was getting before, but the MFD is now reading lower. Is it possible that the dealer made a software update, or something similar, that is causing the MFD mileage to be calculated lower? Ironically, prior to the service, my MFD tank mileages were consistantly 2-4 mpg higher than the "real mileage" as calculated by gallons pumped/miles driven. After the service, they now agree fairly closely. One parameter change that may complicate this is that the air temperature in my area (Phoenix) has dropped from 90 to 70 during the interim time period, perhaps altering the bladder rigidity? __________________ Tideland Pearl '05 Prius Imperial Jade Mica '01 4wd Tundra

11-13-2005, 01:53 PM	#5
DaveinOlyWA 3rd Time was Solariffic!! Join Date: Apr 2004 Location: South Puget Sound, WA Posts: 12,378 My Car: 2010 Prius Model: IV Package: Solar Roof Thanks: 24 Thanked 121 Times in 103 Posts Friends: 10	its the temp change. 20º is more than enough to change a few miles or so. one thing i found it that the hotter it is, the better the mileage if all else is equal. usually most, especially people in your area, wouldnt notice because the air would negate any major differences. keep in mind that if your commute is long, the difference wont be as much, since temps are only going to affect the first 5 mins of driving. i drive an 8.8 mile commute. this past summer i would drive in the morning and lose +/- .1-.2 mpg on my tank. in the evening, i would gain .2-.3 mpg. no elevation changes to speak of, only difference was that my car in the evening would still be very warm from the heat of the day. (i got off work at 7-8 pm...sun doesnt set till 9-10 pm) didnt use air 90% of the time because i prefered the down window thing. (commute speeds never exceed 40 mph) so even with the loss of aerodynamics from the down windows, my mileage still improved. so yes, temp plays a huge roll... in some cases. __________________ My Blue 2010 : Last tank 541.9 @ 49.48 pump (56.7 MFD) 5.54 CPM, 21 MPH, Lifetime:5442.2 miles 56.5 MPG pump. (62.22 MFD) 4.72 CPM. Summer MPG 57.4 Winter: 49.5 My 2006 SPM: Last tank 376.6 miles @38.21 pump (40.8 MFD) 7.17 cpm winter mpg 49.64 summer mpg 53.41 lifetime: 42,563.5 miles 51.5 mpg pump (52.7 mpg MFD) 5.51 cpm My 2007 Zenn total "fuel cost" $166.58 on "about" 9599.7 miles. 1.74 cents per mile (granted i plug in for free at work!!) My Plate: DUALPWR (Dual Power)

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11-13-2005, 12:04 PM	#2
Jaguar88 Senior Member Join Date: Apr 2005 Location: La Crescenta, CA Posts: 172 My Car: 2005 Prius Model: Package: #3 Thanks: 0 Thanked 0 Times in 0 Posts Friends: 0	Check the oil, its been reported that an overfill reduces milage.

11-13-2005, 01:32 PM	#4
galaxee resident lab rat Join Date: Mar 2005 Location: boilermaker territory Posts: 9,675 My Car: 2005 Prius Model: N/A Package: #5 Thanks: 0 Thanked 94 Times in 37 Posts Friends: 26	did they rotate tires? may be secondary tire break-in.

11-13-2005, 02:03 PM	#7
Maytrix Senior Member Join Date: Aug 2005 Location: Marlborough, Mass Posts: 734 My Car: 2005 Prius Model: Package: #6 Thanks: 0 Thanked 1 Time in 1 Post Friends: 0	Hey Gang, I think everyone has missed the point. His actual calculated mileage has NOT changed. Just the readout on the MFD. IF he had 50mpg on the MFD on most fill ups prior to service, it sounds like it's now reading 47 or something lower. Eitherway, it sounds like whatever caused the change, has just helped since it's made your MFD more reliable.

11-13-2005, 02:34 PM	#9
DaveinOlyWA 3rd Time was Solariffic!! Join Date: Apr 2004 Location: South Puget Sound, WA Posts: 12,378 My Car: 2010 Prius Model: IV Package: Solar Roof Thanks: 24 Thanked 121 Times in 103 Posts Friends: 10	i understand what he is saying and i went through the same thing last year. another thing you might want to look at is the mileage you now have. when i first got my Prius, the MFD was consistantly 1-2 mpg higher on the average. as time went by, the difference became smaller. the bladder stretching a little bit would cause this right? so i accepted this. but then right at this time last year, same mileage (well actually about 8,000 on mine) boom, the difference bet the two readings started to shrink and that can only partially be due to the bladder's not expanding anymore. so then you look at other changing factors and temp was the only measurable variable that i could see also... now is this conclusive? after another year, the difference is now that my tank mileage has swapped places with the MFD mileage but the change has slowed considerably. but will have to wait out another winter to see what trends develope... too early yet. the other thing i can say to this...if this aint the right answer then you need to DUMP YOUR DEALER!! if he is performing maintainence behind your back, get out while you can'!! i dont care what the procedure is or how critical it is. if someone does something to my car without telling me about it first, it will be for the last time also, i really think you simply need more data before any real conclusions can be made.

11-13-2005, 02:51 PM	#10
jbarnhart Senior Member Join Date: Jan 2004 Location: Santa Clara, CA Posts: 629 My Car: Model: Package: Thanks: 0 Thanked 0 Times in 0 Posts Friends: 1	It stands to reason that there are coefficients in the onboard computer that will affect the accuracy of the MFD milage calculation. The Prius is offered with several different tire combinations in other geographies, for example. The MFD milage calculation needs to know the outer diameter of the tire for its distance calculation, so an incorrect setting would cause errors in the reported milage. There could be other internal settings which also affect this number. Sounds like the dealer may have caught an error and fixed it.