Question for everybody: Does anyone know how the FEH computes the Miles To Empty (MTE) value for the in-dash display?

I think that it is safe to say that the system cannot - and will not - be perfect in its calculation, for any number of reasons. Aggressive driving, temperature (internal or external), type of gasoline, and several other factors can influence fuel economy and therefore MTE.

My question stems from watching my MTE display change in a non-linear manner, despite keeping my FE (according to the NAV display) in a constant range of 34.2 - 34.4 MPG for almost the entire tank.

Examples:
After driving 75 miles after fill-up, MTE = 436. Total miles/tank = 511.
After 125 miles, MTE = 385. Total = 510.
After around 200 miles, MTE = 290. Total = 490.
After around 240 miles, MTE = 235. Total = 475.
And currently at 308 miles after fill-up, MTE = 160. Total = 468.

I'm curious how the computer-calculated MTE can fluctuate by a range of almost 50 miles/tank (=1.46 gal assuming 34.2 MPG). I recognize that at "0 MTE" the FEH has about 1.3 gal of open space in the tank...is the fluctuation just accounting for that space? If so, why isn't it reflected right after fill-up?

The MTE display isn't the most important feature on the FEH, and if its inaccurate by nature than so be it. Other 2008 owners know that the gas light goes on at 50 MTE regardless of fuel economy, and at least IMO its a kinda large/distracting light. Thus, maximixing my miles/tank is not only a personal goal, but a means to eliminate that distraction. If anyone has any thoughts, comments, or explanations, I'd appreciate it. Thanks!

 

You have a light?

That's interesting, the older version does not, just a note on the message center about low fuel. Actually, coming back from Hybridfest, I ran well past 0 MTE, knowing that there was quite a bit of reserve in the '06 tank that the MTE doesn't use, and was a bit surprised that there was no further alarms beyond the message centers low fuel warning, which goes away when you hit set.

Mine seems most directly influenced by the MPG that it's calculating. As it rises, I tend to get more, and when I go faster, it drops.

The '08 system appears to be different.

 

On the 08 I have noticed that the mte does change with the avg mpg by not actually counting mile for mile. In other words when your avg mpg is low, it actually causes the mte to calculate (drop off more than a mile to empty in one mile). as an exaggerated example if your mpg was lets say very poor, the mte might take off two miles mte for every one mile of travel. That is an example only so please don't anyone do the math and say that is too severe! On the other hand when my mpg is very good I notice that one mile on the odometer does not subtract one mile from the mte display.

Hope this makes sense.

My fuel light also comes on at 50 mte.

Also I have run the tank down as low as 9 mte and it took 14.3 gallons to fill up. If the tank in the 08 is really 15.0 gallons as the manual says, I'm not so sure I would chance going much further as I am sure the pick-up sock is not exactly at the bottom.


08FEH

 

The MTE display comes from a running history of your mileage as well as instant MPG. I find resetting my average MPG does not reset the running history. My daughter a year or so ago took my FEH to Orlando and back (about 400 miles RT) and dropped my MTE from low 600's to around 500 MTE. Her mileage was much worst than having a 500 MTE reading at fill-up, but the computer still used old data to keep the MTE at 500 miles to empty. When I began to improve the average, it was a long process to get my average back in the 600's. With the cool winter, I maintained above 50mpg for a few tanks and took this picture you see on this page below. This is all about fill-up and that reading.

Once you start draining the tank after filling up, the computer starts using the new MPG data and adjust your remaining MTE accordingly. If your mileage is better than the history average at fill-up, your MTE number will increase. The same thing if you get worst mileage, your MTE will get lower. The computer uses the history data because it's the only way to keep the MTE estimates from going all over the place at fill-up.

GaryG

 

Thanks for the responses, all.

I believe a few other 08 owners have reported the gas light at 50 MTE, so that part I'm not concerned about (although I am still hoping to delay its luminesence for as long as possible).

I guess I was just surprised at seeing a non-linear MTE change whlie keeping my NAV MPG in such a constant band. As others have commented, it does work the other way - - a few times I've seen the MTE increase by one mile while driving in EV ..... but I've also seen MTE decrease while in EV, so go figure.

If any other owners have thoughts, comments, or experiences I'd still like to learn more. If there is a way to best "teach" the 08 FEH I'm all for it. It's just frustrating to see the MTE drop by sometimes 5 miles after driving a 2 mile stretch of road.

 

MTE uses historical MPG, and current fuel level info. The fuel level can change with vehicle acceleration,braking, orientation, etc. I have had extremely high MPG readings after refueling and going EV, but my MTE never gets that high. The scanguage reading, though, was over 1200!

 

I try to keep in mind the scangauge II requires user input. If the user input is faulty then the scangauge can be faulty. A previous thread on a similar topic in this website did question the accuracy of the fuel pumps we use at the gas station. If my memory serves me correctly, this poster stated the fuel pumps rely on "back-pressure" to shut off delievery. My experience with the scangauge II is it will read several tenths (0.2 to 0.4) of a gallon difference from the fuel pump when I do a normal fillup of approximately 12 gallons. What figure do we now use for gallons to fillup the tank-the scangauge II or the fuel pump?

 

I had asked this a while ago and the responses I got were along the lines of it's a little MPG, a little distance in time. I always go past 0 MTE, and so far the most miles I've gotten on a tank has been 459. Of course, I'm a chicken (having run out of gas twice before) so I never push it, and I've never put in more than 13.5 gallons of gas. My MTE lately has been starting at 510 or so, then as soon as I take off it drops into the 490 range. Perhaps it's because the vehicle is in hybrid when it first calculates the MTE? I should jest try to hit 475 and see how much gas it takes, then bump up again on the next tank (although my mileage has dropped 1 MPG on this tank; no idea why [limited AC use; similar air temps to last tank, when I ran my AC a lot]).

 

You can be sure you have 1.0 to 1.3 gallons left when the car says MTE 0.

So you need to estimate how far that will take you based on current condition. Best case? I've gone 50 miles past zero. Now, if you are climbing a mountain, with A/C on, you may only wish to go 20 miles past zero.

Just remember you always have at least 1 gallon past empty. Usually more.
-John

P.S. I see the same thing. My car will say, for example: 560 miles to empty at a fill up. Then, when it says MTE 0, I have only gone 500 miles. I can usually squeeze out 50 more miles past zero with FE driving, getting back to nearly the original estimate.

 

What about state of charge of the hybrid battery and a recent history of use or non-use of hybrid capability?

34 MPG with a fully charged hybrid battery and a recent history of lots of regenerative braking to recharge the hybrid battery would be a lot different in a DTE calculation vs 34 MPG HWY use with virtually no recent history of braking regeneration and a low hybrid battery charge.