What accounts for this?

[Shawn Clark]

Originally Posted by hobba

My car is FL based, so the heat surely keeps the bladder as soft and expandable as possible. The MFD is very close in reporting MPG vs. my excel Prius spreadsheet calculator. As previously stated, my MPG for 3 years was within two or three MPG. The variations I'm seeing now are huge. In one case, 51 MPG and then 26 MPG on the next tank.

For those cases you mention can you give the specific calculated and MFD values? Are they roughly 51 MFD, 51 calc., and 26, 26? That would indeed be pretty alarming unless you had some sort of assignable cause like dragging a battleship anchor for the whole tank.

Or are the pairs more like 51, 26 and 26, 51 respectively? This would indicate tank fill/gauge variability.

[DaveinOlyWA]

for one thing, the bladder will always provide inconsistent fills, so only look at the average over a minimum of 3-4 tanks.

also, the next time you fill up and get about the same mileage on the pump AND the MFD. remember that for your next fillup because that is mostly a good fill.

now, suppose you drive 450 miles and MFD says 50 mpg... you fill up, it stops at 8 gallons, what do you do? stop? well, what i do, is i say, i should have used 9 gallons, so i will go up to at least 8.8 gallons or so. if you dont, you will most likely be short and the next tank will fill more making it look like you have mileage in the mid 30's...to be honest with ya, that is not an easy thing to do. only during the extremes of winter do i even get close to that... (actually only got as low as 39 mpg). for you, its the hot weather and right after i got my 2004 Pri, i was new to hybrids so wasn't used to getting great mileage. had a hot spell of 3 days (twice at or over 100º) then went to Montana where it was in the 90's for another 3 days. had the A/C blasting and still got almost 50 mpg

the reason i started doing this is because some pumps dont work correctly and auto shut off will happen too early. after it clicks off once, your choice is to trickle in the amount you feel should be in there, or wait about 5 minutes for any fluid in the valve to drain back so it will work properly again.

[hobba]

I have had the dealer look at all these issues, something dragging, a brake hung up, etc. Even corporate Toyota has been involved. They had the fuel system and injectors cleaned and still the wild swings in MPG. This all began in May of last year and is part of the "After Service Issue" thread I started back then. So the crankcase is not overfilled and the tires are at 42/40. If it helps, I can post my tank to tank MPG numbers for those of you who might be interested, but for now, Toyota corp., and my dealer are stumped. The car runs and acts fine.

[qbee42]

So are you saying that your *actual* mileage is varying between 50s and 20s? Let's get this straight so that we know the real question.

Tom

[Shawn Clark]

Originally Posted by qbee42

So are you saying that your *actual* mileage is varying between 50s and 20s? Let's get this straight so that we know the real question.

Yes, that is what I was asking as well. The two consecutive tanks mentioned previously were very curious and could provide a basis for narrowing the focus.

[richard schumacher]

Originally Posted by hobba

This all began in May of last year and is part of the "After Service Issue" thread I started back then.

1. So what happened last May, just before this started?
2. Unless Toyota USA has already sent an engineer to diagose it, take it to another dealer.
3. Has anyone looked at the throttle plate and the mass air flow sensor?

[hobba]

Here is the MPG for the last 12 tankfuls. The MPG as calculated by the MFD vs. the spreadsheet have varied by 0.2 to 0.4 MPG, hardly enough to be significant.26.0438.8238.9941.8036.9344.1139.0754. 1237.1143.2248.3935.67To answer Rich's questions:1. After having the car in for routine service at Toyota for oil, filter and rotation, the problem began.2. Toyota has send a regional guy to look at it and found nothing. The other Toyota dealer in town has a terrible service dept.3. The throttle plate and mass air flow sensor were looked at by the regional guy and found to be operating in spec.

[Rokeby]

Hobba,

When rational answers can't be found, it's time for a conspiracy
theory.

Are you the only driver of this car?

Is it possible that at random intervals/distances another driver cranks
the air co way up?

Could that same person be also adding some fuel -- a couple of gallons,
$5 =~2 gal -- at random intervals?

For the latter, I'm going on the idea that when empty the car needs
more than 3 gals for it to to be shown on the guess gauge. In turn, if
it's not registered on the guage, then maybe it wouldn't reset the miles
travelled on a tank display, and would then go unnoticed by you.

A long shot for sure.

[Shawn Clark]

Hobba, that post could really use some spaces, commas or something to put it in a recognizable form.

[hobba]

Sorry for the MPG figures. I guess I can't cut and paste from Excel. Here are those numbers again from most recent fill to include the previous 12 tankfuls.

35.6, 48.3, 43.2, 37.1, 54.1, 39.0, 44.1, 36.9, 41.8, 38.9, 38.8, 41.7

The tank with 26.9 mpg was further back and bracketed by 42.4 and 45.0.