Why the top fuel level bar lasts so long

[CTScott]

There have been quite a few threads in the past that discussed this, but here's a Mythbusters style analysis of it (fortunately, minus the large explosion at the end):

Today I am working on the range until empty and fuel level in gallons (or liters) features for my YarGauge project. I drained Crashy's fuel tank and then added 1 gallon (precisely measured with a one gallon laboratory flask) at a time while recording the data values from the analog to digital converter, which I have connected to the fuel level input to the instrument cluster.

I plotted a graph to see how linear (or not) the fuel sender value is in regards to the volume in the tank. From bone dry to the top of the filler pipe, I was able to put in 12.8 gallons. The ADC value stops changing at just over 11 gallons.

So, you can put just shy of two gallons more into the tank than the fuel gauge can measure.

31330

[b_hickman11]

There have been quite a few threads in the past that discussed this, but here's a Mythbusters style analysis of it (fortunately, minus the large explosion at the end):

Today I am working on the range until empty and fuel level in gallons (or liters) features for my YarGauge project. I drained Crashy's fuel tank and then added 1 gallon (precisely measured with a one gallon laboratory flask) at a time while recording the data values from the analog to digital converter, which I have connected to the fuel level input to the instrument cluster.

I plotted a graph to see how linear (or not) the fuel sender value is in regards to the volume in the tank. From bone dry to the top of the filler pipe, I was able to put in 12.8 gallons. The ADC value stops changing at just over 11 gallons.

So, you can put just shy of two gallons more into the tank than the fuel gauge can measure.

31330

This is not only on the Yaris. Every car or truck I have owned has the same "problem" as the Yaris. It's the norm.

[CTScott]

This is not only on the Yaris. Every car or truck I have owned has the same "problem" as the Yaris. It's the norm.

Exactly. Because the level sender is in the tank and the fill pipe is above, this will always be the case. I just thought it was interesting to see the data on where the real cut off is.

[DerFlosser]

Cool Scott! Confirmation is always a good thing.

[BailOut]

That's a great data set, CTScott. Thanks for sharing it. :smile:

[Kal-El]

Thanks for this project scott! It's nice knowing what the actual capacity of the tank is since we never fill up from bone dry to find out. 12.8 gallons vs the 11.1 capacity that is the official spec. So approximately 1.7 gallons over the gauges "full" level. Certainly explains the extra 50 or so miles we get out of the first bar!

:thumbsup:

[ddongbap]

+1. CTScot for president of something.

[jh3cuemd]

nice investigation CTScott, pro-like! :respekt:

[tk-421]

Thanks for the great info as always, Scott!

here's a Mythbusters style analysis of it (fortunately, minus the large explosion at the end):

You have to admit it would've been awesome to see though... :laugh:

http://www.yarisworld.com/forums/attachment.php?attachmentid=31330&d=1264363566Do you know how each fuel bar correlates to those graph values? It would be nice to see when the fuel meter comes goes down from 3 to 2 bars, for example.

[41magmag41]

Thank you Mr. Scott. Always wondered why the first few gallons went so far. Nice to know we can stuff almost 13 gallons in the tank.

[CTScott]

Thanks for the great info as always, Scott!



You have to admit it would've been awesome to see though... :laugh:

Do you know how each fuel bar correlates to those graph values? It would be nice to see when the fuel meter comes goes down from 3 to 2 bars, for example.

It's pretty gray as far as the bars go. They're bands are quite wide and the cluster's computer takes quite a while to decide that it's OK to update the level.

I understand why, as driving around and watching the real-time raw data, the fuel sloshes like crazy and the level bounces over a range of 2-4 gallons.

[Yaris Hilton]

The gauge has to be averaging the level over a fairly long period of time.

Yesterday I parked mine in the garage and shut it off with the second bar showing on the gauge. When I started it up again a few hours later, it came on with the last bar blinking. Never saw it do that before. I figure it had just reached the threshold for changing bars, but it hadn't been there long enough before I switched it off.

[TheSilkySmooth]

Thanks scott! I have been checking my fuel mileage the old fashioned way, and filling the tank pretty full (to second pump clickoff on slow fill) was wondering how well the evap system can deal with an overfull tank w/o flooding the canister or the purge lines and causing trouble.

[CTScott]

Thanks scott! I have been checking my fuel mileage the old fashioned way, and filling the tank pretty full (to second pump clickoff on slow fill) was wondering how well the evap system can deal with an overfull tank w/o flooding the canister or the purge lines and causing trouble.

The evap vacuum line connects at the top of the filler pipe, so theoretically it will only get wet when you overflow the filler pipe. Although, if the filler pipe is very full (but not overflowing) it is quite possible for the fuel to slosh around enough to get some where it shouldn't be.

[kameele]

CT--there's no end to what Crashy can do!! it's nice to know that there is a little more capacity than the spec says. i know nothing of the structure of the gas tank. is there any heel left when the level hits the gas line? That is, any un-useable gas left behind?

[CTScott]

CT--there's no end to what Crashy can do!! it's nice to know that there is a little more capacity than the spec says. i know nothing of the structure of the gas tank. is there any heel left when the level hits the gas line? That is, any un-useable gas left behind?

For the test, I started with the tank less than half full. I drained it by disconnecting the filler pipe from the tank and using a hand pump to siphon the gas. I drained it until the pump was sucking air and the bottom of the tank had less than 1/4". I started the car to see if it would start and run for a bit and after about 5 minutes I got bored and shut it off and started grabbing my data. The bottom of the tank is flat with a couple of ridges for strength, so I think it still running was due to the well within the sender unit.

Here is what the bottom of the tank looks like. It is basically flat with a small recess where the sender unit sits.
31345

Here is a view of the sender unit, looking down into its well where the fuel pump sits. You can see the circle facing the float which is the intake.
31346

[kameele]

So basically, if you run out of gas, the tank is dry.

[CTScott]

So basically, if you run out of gas, the tank is dry.

Very close to dry. When it stops running the bottom of the tank is barely covered.

[HerrDeacon]

Thanks for posting this CTScott. I just recently bought a Yaris and I'm still on my first tank, but I did wonder why the top bar lasted so long compared to the others...well now I know, thanks.

[Yarrris-Wench]

+1. CTScot for president of something.

+2!! This is quite interesting!:respekt:

[why?]

don't run this tank dry. If the car stops because of no fuel, you will not be able to get it started again at all, and will have to go get gas. i did it once, trying to see how far I could go on a tank of gas. I've never had a car that just simply refused to start like the Yaris did.

[Kal-El]

don't run this tank dry. If the car stops because of no fuel, you will not be able to get it started again at all, and will have to go get gas. i did it once, trying to see how far I could go on a tank of gas. I've never had a car that just simply refused to start like the Yaris did.

:confused:

Am I reading this right? You're wondering why the Yaris won't restart after you stall out by running it dry?

Hint: gas powered cars do not run without gas. :wink:

[CTScott]

:confused:

Am I reading this right? You're wondering why the Yaris won't restart after you stall out by running it dry?

Hint: gas powered cars do not run without gas. :wink:

I know what he means. On some cars, when they run out, you can restart them, and drive them gently (to keep the last bit of fuel as stationary as possible) a bit until they die again. The way the Yaris' fuel system works you can't - Once it quits, it's done.

[tk-421]

@CTScott: Is there a way to measure (in a more precise manner) how much fuel is left in the tank by using an OBD module?

[CTScott]

@CTScott: Is there a way to measure (in a more precise manner) how much fuel is left in the tank by using an OBD module?

Not really. There isn't an OBD command for fuel level. If we knew the secret Toyota handshake, I could poll the cluster for the fuel level, but that would be the same latent data that the fuel gauge shows.

The problem with doing it by fuel flow is that it is one way. Unless you could also read the flow rate into the tank, you'd still be working down from an approximation.

[CTScott]

why would you need a two way? if we would be able to read the fuel flow, then each time you would fuel up you would input the amount into the ucontroller and then just use the fuel flow to calculate the instantaneous fuel level. you could program the ucontroller to always take under consideration whatever is left in the tank and then add this amount to the amount you put in at the gas station. not sure if i'm explaining it clearly

I know what you mean. Actually, the fuel flow rate is calculated from the MAF flow rate (there's not a standard PID for fuel flow), so even that is an approximation.

[127.0.0.1]

I know what he means. On some cars, when they run out, you can restart them, and drive them gently (to keep the last bit of fuel as stationary as possible) a bit until they die again. The way the Yaris' fuel system works you can't - Once it quits, it's done.


it will sputter a bit then run good, alerting you that only minutes
remain and you are walking.....


my 4runner does that with <1/2 gallon left


it dies. you stop, wait, start again. in 3 miles it dies again.

start back up, you have 2 miles left, at most

[MadMax]

My favorite Mythbusters explosion! :biggrin:

Mythbusters - Compact Compact Rocket Sled (http://www.youtube.com/watch?v=aSVfYwdGSsQ)

Thank God it wasn't a Yaris at the end! :eek:

Cheers! M2

[Idahotom]

100 % useable? great! I don't much care how long the first bar or two takes, its the apparent speed up of the flashing last bar, usually when I'm some distance away from a station, that always gets me by surprise. My other Toyota is exactly the same in that respect, it seems to go from 3/4 empty to empty real quick, I've learned to ignore it, to some extant, and have never run out totally. Knowing what I know now, I'll probably push it even more! 10.48 gallons at my last fillup, just right.

[OTA'sTOY]

commom sense will tell you if you close to empty
"only got 1 bar left" ....get gas....
pay now or pay later

[nookandcrannycar]

There have been quite a few threads in the past that discussed this, but here's a Mythbusters style analysis of it (fortunately, minus the large explosion at the end):

Today I am working on the range until empty and fuel level in gallons (or liters) features for my YarGauge project. I drained Crashy's fuel tank and then added 1 gallon (precisely measured with a one gallon laboratory flask) at a time while recording the data values from the analog to digital converter, which I have connected to the fuel level input to the instrument cluster.

I plotted a graph to see how linear (or not) the fuel sender value is in regards to the volume in the tank. From bone dry to the top of the filler pipe, I was able to put in 12.8 gallons. The ADC value stops changing at just over 11 gallons.

So, you can put just shy of two gallons more into the tank than the fuel gauge can measure.

31330

Interesting. This is the first time I've seen or read this post. This jives with what I experienced after running out of gas while pulling into a gas station to get gas. I filled it (as I always do when filling a tank) to the point where I can barely see the gas and the pump registered 12.777 gallons. It stands to reason that the remaining .023 gallons would = any difference between my level and the 'top of the filler pipe' CTScott describes and the small amount in the bottom of the tank that CTScott describes in a later post to this thread.

[nookandcrannycar]

don't run this tank dry. If the car stops because of no fuel, you will not be able to get it started again at all, and will have to go get gas. i did it once, trying to see how far I could go on a tank of gas. I've never had a car that just simply refused to start like the Yaris did.

I have a AAA Plus membership and the Yaris is so reliable that since purchasing it the only tangible value I've gotten out of the membership is when I've run out of gas. The intangible value of the peace of mind the membership confers is, to me, worth the cost. For some people, re location, a AAA membership would be a waste of money. I used to live part time in Mammoth Lakes, California. I didn't need a car to get around, but I had my car there anyway. I locked my key in my car. I called AAA and they couldn't help me. The maximum range from a contract station at that time (on my membership) was 50 miles and no contract station existed within 50 miles of Mammoth Lakes. I had to wait until my girlfriend could bring me another key on her next visit from Orange County.

[DonM]

I don't understand why anyone would want to let their fuel level drop to less than a 1/4 of a tank as I was always under the impression that any crud that may have been accumulated from using "dirty" gas is usually sitting at the bottom of the tank.

I know of 2 people who ran out of gas and a short time later - their fuel pumps died (one of them was a Chev Montana van and the cost to repair the fuel pump was $750.00).

[rningonfumes]

I almost always run it down leaving just about 1 gallon left. It helps me to keep track of my mileage more efficiently (by glancing at the trip meter). As soon as the last bar blinks, I use the trip meter to confirm how much gas I have left and plan the gas run accordingly.

[why?]

I have a AAA Plus membership and the Yaris is so reliable that since purchasing it the only tangible value I've gotten out of the membership is when I've run out of gas. The intangible value of the peace of mind the membership confers is, to me, worth the cost. For some people, re location, a AAA membership would be a waste of money. I used to live part time in Mammoth Lakes, California. I didn't need a car to get around, but I had my car there anyway. I locked my key in my car. I called AAA and they couldn't help me. The maximum range from a contract station at that time (on my membership) was 50 miles and no contract station existed within 50 miles of Mammoth Lakes. I had to wait until my girlfriend could bring me another key on her next visit from Orange County.

So true. When I was working in florida I lost so many keys I had to call for locksmiths far too many times. At this point I always walk around with at least 3 keys on me. I wouldn't ever get in a car without a valid AAA membership.

I don't understand why anyone would want to let their fuel level drop to less than a 1/4 of a tank as I was always under the impression that any crud that may have been accumulated from using "dirty" gas is usually sitting at the bottom of the tank.

I know of 2 people who ran out of gas and a short time later - their fuel pumps died (one of them was a Chev Montana van and the cost to repair the fuel pump was $750.00).
Never using bad gas is the easy way to fix this. Everyone knows what the good gas is in their area, you should keep to it. Where I live, the two best gasses actually help to increase gas mileage as well.

Not to mention if you run the tank lower, none of that crud ever has the chance of building up since it is all used.

[DebbyM46227]

I never let my car run out of gas, but I have the same thing as AAA included in my car insurance. It covers towing, flat tire changes, locksmith, battery jump-starts, and fuel/fluid delivery for $2.00 addl. every 6 months. So far, haven't had to use it with my Yaris for anything (knock on wood) but when I had the Cavalier I took advantage of it 3 times for flat tire changes.

[nookandcrannycar]

So true. When I was working in florida I lost so many keys I had to call for locksmiths far too many times. At this point I always walk around with at least 3 keys on me. I wouldn't ever get in a car without a valid AAA membership.


Never using bad gas is the easy way to fix this. Everyone knows what the good gas is in their area, you should keep to it. Where I live, the two best gasses actually help to increase gas mileage as well.

Not to mention if you run the tank lower, none of that crud ever has the chance of building up since it is all used.

Come to think of it, I have used my AAA membership at least once with my Yaris. I also once locked my keys in my Yaris and avoided having to call AAA due to help from a beautiful woman. I have a nationwide membership with a well known fitness club chain. One of my fairly local clubs shares a parking lot with a Starbucks. I left the Starbucks, walked up to my car, and realized I had locked my keys in the car. I walked across the parking lot to the fitness club. I checked I with the 'new' method (fingerprint and phone number) and used the mens room. I returned to the same rep who saw me check in (the beautiful woman) and explained what happened and that my phone was also in my car. She said "I have a better idea, follow me". She walked up to the strongest and toughest looking guy in the entire gym and explained my situation and asked him if he would unlock my car (he is a tow truck driver). He smiled and said "Anything for you, darlin". He immediately left his station and I walked with him to his truck, where he picked up the needed equipment, and we walked to my car and he unlocked it for me. Nicest guy in the world.

[nookandcrannycar]

I don't understand why anyone would want to let their fuel level drop to less than a 1/4 of a tank as I was always under the impression that any crud that may have been accumulated from using "dirty" gas is usually sitting at the bottom of the tank.

I know of 2 people who ran out of gas and a short time later - their fuel pumps died (one of them was a Chev Montana van and the cost to repair the fuel pump was $750.00).

....218,480 miles on original fuel pump still doing its job in my car. Also see Why?'s reply about quality gas and level within gas tank.

[NEexpat]

Trying to get my UltraGuage more accurate as it relates to MPG.

Currently it is set-up to an 11.1 gal. tank.

I always fill to the first click, round to the nearest nickel.

Based on CTScott's examination and testing I am thinking of resetting my tank size to 11.9.

Would I be correct in assuming that a first click fill up would add an additional .7 gal.,apprx.?

Or would increasing the the tank to 11.6 an additional 1/2 gal. be closer?

I am thinking .8, any thoughts would be appreciated.

[CTScott]

Trying to get my UltraGuage more accurate as it relates to MPG.

Currently it is set-up to an 11.1 gal. tank.

I always fill to the first click, round to the nearest nickel.

Based on CTScott's examination and testing I am thinking of resetting my tank size to 11.9.

Would I be correct in assuming that a first click fill up would add an additional .7 gal.,apprx.?

Or would increasing the the tank to 11.6 an additional 1/2 gal. be closer?

I am thinking .8, any thoughts would be appreciated.

For the first click, I would say that 11.6 - 11.7 is good. If you go a bit beyond that then 11.8 to 11.9 would be appropriate.

[NEexpat]

Thanks Scott.

I think I will try 11.6 for a bit and compare to actual at the pump.


EDIT note: Would I be correct in assuming that a first click fill up would add an additional .7 gal.,apprx.?

That should be ".8"

[fnkngrv]

^ this