Low fuel indicator and accuracy of distance remaining indication
11-22-11, 05:39 PM
#32
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Strange as it may sound, I do put some trust in fuel gauges. They've always treated me right ever since I started driving in 1966, but, like a lot of other consumer products nowadays, maybe they're not as good as they used to be. (You know how Ford, a few years ago, suddenly forgot how to make cruise controls that didn't cause a fire in a truck.) Maybe Lexus knows that their fuel gauge/light are not as reliable as they used to be and that's why they don't tell their consumers approximately how much fuel is left in the tank when that indicator comes on and stays on. Our 1992 Accord's owners manual has that information, but maybe that was from the era when cars still had reliable gauges/indicators and manufacturers felt comfortable putting that sensitive information in an owners manual.
To those who are skeptical of fuel gauges, I recommend you fill up when the needle reaches half full. Better safe than sorry.
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Again, for me, peace of mind comes from knowledge, not ignorance. But this is a new age and new technology, so to protect the sensitive, maybe a moderator should put a warning on the thread title that indicates that the thread contains fuel system information that is intended for those who can "handle" it.
11-22-11, 05:48 PM
#33
My personal guess is that it is approximately 2.5 gallons and may vary from car to car. The corresponding remaining range is then calculated based on the average mpg on that tank. When I refill the readout always says remaining range over 400 miles but I always get over 500 miles on a tank as I don't do very much city driving, mostly burbs to the sticks.
Past Performance is No Guarantee of Future Results
Don't repeat this at home.
Please no "Watch This" posts.
Past Performance is No Guarantee of Future Results
Don't repeat this at home.
Please no "Watch This" posts.
Last edited by hoonunya; 11-22-11 at 05:57 PM. Reason: add a lighter touch at the end.
11-22-11, 09:06 PM
#34
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How accurate are you trying to get? The range in the display goes down to 30 or 35 miles left before it switches to "low fuel" in the display. It uses your tank average mpg to determine range, so it should be just about right as long as your last 30 miles are not a significant deviation in driving conditions than the rest of the tank. I thought the light on the gauge came on when range was 50 miles, but if it doesn't, just flip over to your tank average on the display when the light comes on and see what it is calculating from. If tank average is 20 mpg and the light comes on with 60 mile range, then it is basing the light on 3 gallons. You can confirm your hypothesis on the next tank.
As for the 1992 Accord, they may have informed you of the level at which the light came on, but you apparently need to make the calculations on the fly to determine your fuel mileage and make an estimate of your remaining range provided you notice exactly when the light comes on, as there was no informational display in the car. Also, I'm sure it would be rather difficult to obtain the variance of the fuel level sensor, since both mechanical and electronic sensors in fuel tanks are subject to a variety of external and internal factors that can easily throw off the reading by small amounts, such as the car leaning to one side, temperature, voltage, vibration in the tank, delay interval, etc. Further, your calculation to determine the average mpg to the point of the light coming on would be based on the assumption that the tank was completely full, which also could vary depending on the fuel station's pump accuracy and shutoff pressure, leading to an incorrect determination of how far the remaining 2.5 gallons will take you, even if the gauge were completely accurate and reliable.
In the end, the gauge light and the informational display in the LS are likely more accurate than the manual calculations you were making in the Honda, with the added bonus of not having any human error variable. The assumption that the gauge in the Honda was more accurate because the manual stated the trigger point for the light is a fallacy, as gauge accuracy is not dependent on the manufacturer publishing the trigger point for the light. It could be reasonably deduced in the alternative that manufacturers no longer need to publish that information due to the increasing accuracy of the gauges and the information available in the display. If the car tells you with reasonable accuracy how many miles you can drive, why would anyone need to know the trigger point of the fuel light? Maybe they don't want you using a calculator while driving.
If you drive an extra 10 miles per tank, with an average of 400 miles per tank, you will save yourself the inconvenience of one fill-up every 16,000 miles. That's a lot of risk for pretty little return, seeing as you could find yourself in stop and go traffic or in an emergency during your last gallon and end up stranded because you don't even have a safe level of fuel in the vehicle.
I'd recommend just trusting the informational display and filling up when your indicated range is less than what you are comfortable with. It is no less accurate than any other method of measurement, as you will never have an exact reading shy of weighing the vehicle in, weighing the vehicle out, and using an inline fuel meter to determine the exact remaining contents of the tank. If "approximation" is your goal, as you stated, the car is already doing it for you.
Just to be clear, the "Display 1" button on the wheel will cycle through the options available on the informational display in the dash cluster so you can view your range and not have to rely on the light near the fuel gauge.
As for the 1992 Accord, they may have informed you of the level at which the light came on, but you apparently need to make the calculations on the fly to determine your fuel mileage and make an estimate of your remaining range provided you notice exactly when the light comes on, as there was no informational display in the car. Also, I'm sure it would be rather difficult to obtain the variance of the fuel level sensor, since both mechanical and electronic sensors in fuel tanks are subject to a variety of external and internal factors that can easily throw off the reading by small amounts, such as the car leaning to one side, temperature, voltage, vibration in the tank, delay interval, etc. Further, your calculation to determine the average mpg to the point of the light coming on would be based on the assumption that the tank was completely full, which also could vary depending on the fuel station's pump accuracy and shutoff pressure, leading to an incorrect determination of how far the remaining 2.5 gallons will take you, even if the gauge were completely accurate and reliable.
In the end, the gauge light and the informational display in the LS are likely more accurate than the manual calculations you were making in the Honda, with the added bonus of not having any human error variable. The assumption that the gauge in the Honda was more accurate because the manual stated the trigger point for the light is a fallacy, as gauge accuracy is not dependent on the manufacturer publishing the trigger point for the light. It could be reasonably deduced in the alternative that manufacturers no longer need to publish that information due to the increasing accuracy of the gauges and the information available in the display. If the car tells you with reasonable accuracy how many miles you can drive, why would anyone need to know the trigger point of the fuel light? Maybe they don't want you using a calculator while driving.
If you drive an extra 10 miles per tank, with an average of 400 miles per tank, you will save yourself the inconvenience of one fill-up every 16,000 miles. That's a lot of risk for pretty little return, seeing as you could find yourself in stop and go traffic or in an emergency during your last gallon and end up stranded because you don't even have a safe level of fuel in the vehicle.
I'd recommend just trusting the informational display and filling up when your indicated range is less than what you are comfortable with. It is no less accurate than any other method of measurement, as you will never have an exact reading shy of weighing the vehicle in, weighing the vehicle out, and using an inline fuel meter to determine the exact remaining contents of the tank. If "approximation" is your goal, as you stated, the car is already doing it for you.
Just to be clear, the "Display 1" button on the wheel will cycle through the options available on the informational display in the dash cluster so you can view your range and not have to rely on the light near the fuel gauge.
11-22-11, 11:56 PM
#35
outside temperature, and air charge temp will greatly effect this. the answer to this question could only be figured properly doing this. also, you will need to know weight. how much crap do you have with you, how fat are your friends
tony1m - so no matter what lexus tells you, you will have to figure a curve for temp, also, you will have to figure out exactly how much you and your wife weigh, plus all the crap you have with you, and dont forget her purse. Also, a formula for your car based on the condition of your emotion systems, and tire pressure would have to be figured. If your tires were off by even a pound it would effect this. also dont forget wind speed and direction. How could you possibly know all of this crap, unless you a mobile weather station?
I really think lexus answered your question well. if i were given that question, i probably couldn't have done any better.
tony1m - so no matter what lexus tells you, you will have to figure a curve for temp, also, you will have to figure out exactly how much you and your wife weigh, plus all the crap you have with you, and dont forget her purse. Also, a formula for your car based on the condition of your emotion systems, and tire pressure would have to be figured. If your tires were off by even a pound it would effect this. also dont forget wind speed and direction. How could you possibly know all of this crap, unless you a mobile weather station?
I really think lexus answered your question well. if i were given that question, i probably couldn't have done any better.
11-23-11, 08:37 AM
#36
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The really important discovery that my experiment revealed to me is that long long before you run out of gas, the gauge needle goes below the "E" mark on the gauge, as shown in my photo.
The irony of the "distance remaining" data is that it disappears when it becomes most useful to this driver. I care very little about whether I've got 300 miles left in the tank or 200 miles. But I do care whether I have 50 miles or 25 miles, etc. Lexus has for some reason decided that that information is of no interest to the driver, or, again, that it would be too inaccurate. Of course Lexus could provide that data anyway and publish its accuracy in the manual or even on the display, but that will never happen in our car.
When all is said and done, I'll keep my eye on that little needle and completely ignore that ridiculous low fuel warning. When the needle is fully on the "E" mark, if I just note the odometer reading, I'll know that I have at least 30 miles remaining regardless of any other condition, except maybe drag racing or driving against hurricane winds. I know that adding 30 to the odometer reading is pretty dangerous to do while driving, but I'm willing to take that chance.
If my wife is a passenger, I'll just tell her to do the addition for me.
The irony of the "distance remaining" data is that it disappears when it becomes most useful to this driver. I care very little about whether I've got 300 miles left in the tank or 200 miles. But I do care whether I have 50 miles or 25 miles, etc. Lexus has for some reason decided that that information is of no interest to the driver, or, again, that it would be too inaccurate. Of course Lexus could provide that data anyway and publish its accuracy in the manual or even on the display, but that will never happen in our car.
When all is said and done, I'll keep my eye on that little needle and completely ignore that ridiculous low fuel warning. When the needle is fully on the "E" mark, if I just note the odometer reading, I'll know that I have at least 30 miles remaining regardless of any other condition, except maybe drag racing or driving against hurricane winds. I know that adding 30 to the odometer reading is pretty dangerous to do while driving, but I'm willing to take that chance.
If my wife is a passenger, I'll just tell her to do the addition for me.
Last edited by Tony1M; 11-23-11 at 10:44 AM. Reason: additional information
11-23-11, 04:28 PM
#39
01-29-12, 06:34 AM
#40
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It is 24 miles each way from my work. I know that if the light comes on I can make 1 more round trip.
Today the light came about 3 miles after I left my home. The readout was saying 56 miles left at that time. With the readout at about 40-43 miles left it switched to read low fuel. When i got back to the station near my home I refilled and it took 21.4 gallons so .8 gallons was left.
I put 547 miles on that tank at an average of 25.6 mpg on the readout for that tank and that also calculates to 25.6 mpg. 360 miles of that tank was interstate usually at about 80 mph.
i'm surprised that the tank mpg readout is that accurrate. The miles left readout is slightly conservative, at least on my car.
I also know that I can drive that 48 mile roundtrip in my LS400 with the light on. i've done it many times.
I haven't run out of gas yet and don't push it in any car that I am not very familiar with.
Today the light came about 3 miles after I left my home. The readout was saying 56 miles left at that time. With the readout at about 40-43 miles left it switched to read low fuel. When i got back to the station near my home I refilled and it took 21.4 gallons so .8 gallons was left.
I put 547 miles on that tank at an average of 25.6 mpg on the readout for that tank and that also calculates to 25.6 mpg. 360 miles of that tank was interstate usually at about 80 mph.
i'm surprised that the tank mpg readout is that accurrate. The miles left readout is slightly conservative, at least on my car.
I also know that I can drive that 48 mile roundtrip in my LS400 with the light on. i've done it many times.
I haven't run out of gas yet and don't push it in any car that I am not very familiar with.
thank you again
01-29-12, 07:24 AM
#41
Lexus Champion
I don't see how anyone could contend that they get a repeatable, accurate readings on how much gas is left when refueling, especially if you are in the area of 0.8 of a gallon. For instance, how do you know when to stop pumping? If you let the pump stop that is one way. But repeatability of a pump shutting off will definitely vary by pump. All pumps have a filter that as it gets dirtier it will slow the fuel rate to the car. That will slow the velocity, which will in turn change when the pump shuts off (a slower fueling rate will allow the pump to pump more before it shuts off). This is a variable that will exist with all pumps, even if you used the same pump in an experiment.
On the other hand, you might choose to try to fill the tank after the pump has automatically shut off. You would have to keep pumping until you can see the fuel or stop from a slight overspill. This volume in the tank neck is a variable that will cause an inaccuracy.
I think it would be nearly impossible to accurately determine a correct fuel volume when you're dealing with an amount this is around 1 gallon. Just my opinion.
On the other hand, you might choose to try to fill the tank after the pump has automatically shut off. You would have to keep pumping until you can see the fuel or stop from a slight overspill. This volume in the tank neck is a variable that will cause an inaccuracy.
I think it would be nearly impossible to accurately determine a correct fuel volume when you're dealing with an amount this is around 1 gallon. Just my opinion.
05-28-13, 07:59 AM
#42
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HELP!! My 2004 LS 430 with 140K miles is great, but it has a problem with the fuel gauge and cruising range when I get below 1/2 tank. I ran out of gas once with the range at 87 miles and the gauge at about 1/4. It really made me mad. The Lexus service said they could find nothing wrong. I took the simple corrective action of NEVER getting below 100 miles remaining range before filing the tank up. Well, then last month I ran out of gas on the interstate with the range showing 123 miles and the needle on the gas gauge well above 1/4......... Once again the Lexus service department says they can find nothing wrong. What do I do?
05-29-13, 08:05 AM
#43
Lexus Champion
HELP!! My 2004 LS 430 with 140K miles is great, but it has a problem with the fuel gauge and cruising range when I get below 1/2 tank. I ran out of gas once with the range at 87 miles and the gauge at about 1/4. It really made me mad. The Lexus service said they could find nothing wrong. I took the simple corrective action of NEVER getting below 100 miles remaining range before filing the tank up. Well, then last month I ran out of gas on the interstate with the range showing 123 miles and the needle on the gas gauge well above 1/4......... Once again the Lexus service department says they can find nothing wrong. What do I do?
05-29-13, 10:20 AM
#44
If you don't want to spend a lot of money chasing part changes, you could just use your "Trip B" as your fuel gage. Just reset it after ever fill up. Then choose the maximum mileage you want to go before refueling. You could use the Trip B as your constant readout, or just check it occasionally.
I always reset Trip A after refueling. I think I should be using trip B for tracking gas usage and use trip A for it's actual intended purpose.
don't have the aforementioned problem though. I have never run out of gas and I hope I never do.
05-29-13, 03:34 PM
#45
Lexus Champion
I use Trip B for fuel tank refills. I always compute the last tank mpg with a hand calculator. I keep an auto log book in my car and enter each and every gas filling. I record date, overall milage, gallons to fill, cost and tank average. I can scan the average mpg column and then notice any significant change and see if it requires action any possible service action. I can also calculate mpg for an entire year for example. I'm kind of a statistical nut and would even make a running plot of mpg and then you can see the normal variation from the average. Further, you can compute plus and minus three standard deviations and plot those limits also. The variation between the upper and lower limits is normal and you cannot nor should not take any action to try to make changes. If a single point falls outside the limits, it means something abnormal has occurred and you should be able to determine what caused it. For instance a road trip will increase your milage and those points might well fall outside the limits. That is a change is the stable process you have been plotting and is not to be concerned about.
Once you been quantifying processes statistically with charting, you can begin to recognize what points would look like without actually having to plot them.
I'll quit now, as I've probably said too much already.
Once you been quantifying processes statistically with charting, you can begin to recognize what points would look like without actually having to plot them.
I'll quit now, as I've probably said too much already.