What is it with the fuel guage and the distance remaining display. It seems to declare a shorter distance remaining than there is in reality. All this assuming the declared fuel capacity is correct. Is there a reserve fudge factor put in?
John
I would think that it is safer to under-estimate remaining distance than over-estimate and leave you stranded. Running the vehicle out of fuel will eventually ruin the fuel pump and can damage the catalytic converter.
Well yes that is what it is doing. if I didn't have that number there i would drive it down to 1/8 of a tank in town. But going by that number, I have to fill up at the 1/4 mark and it is a bit bothersome. I dislike hidden or built in reserves because you start to ignore things over time.
If you do not mind risking damage to your fuel pump and catalytic converter by running the fuel tank low or empty, it is possible to increase the distance indicated in the distance-to-empty display.
It seems to underestimate by quite a bit. Is this adjusted at the dealership with their plug in 'thingy'? Or can I do it? I have never ran a tank dry yet. But having this thing scare me into filling it up at the
1/4 mark is a bit much. Bkut if I could bring myself to not look at it, then I I would run it down to the 1/8 mark. Not a big deal around here.I have not had one of these discance remaining displays before. Sure nobody wants it to overestimate, but to so grossly underestimate only causes it to be ignored.
John
reality.
I made this same observation two years ago about my 2004 ES330. See:
So nobody really knew.
With my last car, an Audi, 1/4 was actually 1/4 of the tank.
If I fill up at 1/4 mark now, it takes 75 % of the stated capacity. Fine.
But the distance to empty number says something like 75 km. (I'm i Canada) but based on my mileage, I should be able to to 135 km to empty.
If it were not for the distance to empty, I would happily run it down to
1/8 of a tank in town. But that number, Grrrrr, scares me into untimely fill-ups.Or is the stated capacity of the tank wrong?
John
untimely
One way to figure it out is to fill your tank and set your trip odometer to zero. Then observe how many miles the range gauge counts down for each 10 miles of driving. If the trip gauge counts down linearly for the whole tank of gas, then it's probably not the cause of the distortion. If it's not linear, then Lexus/Toyota has deliberately skewed the range gauge so that people don't run the tank down too low.
Having just thought of it, I may try this idea myself sometime. The problem is if your driving is not consistently highway, street or a consistent mix of the two, your measurements will be distorted, accordingly. Also, we don't know how the range gauge is programmed. For example, does it assume a 50/50 ratio of highway/street driving or what?
The gauge will not move down in a linear fashion because the float for the gauge moves in an arc like the float in a toilet tank, and the tank has an irregular shape. The primary goal of the fuel tank's design is to fit in a particular space and to be crash-worthy. Shaping the tank so the gauge would move in a linear fashion would reduce the tank's capacity and the vehicle's range.
I believe that the MPG display is derived by calculating distance traveled and dividing it by an estimate of how much fuel was consumed, either from injector pulse duration or from a flow meter in the fuel system. With the same amount of fuel in the tank, a driver with a light foot will get better MPG than a driver with a heavy foot or who is driving in stop-and-go traffic. The system then uses MPG to calculate distance to empty. You can increase the distance-to-empty reading at any time by driving at a steadier speed than you were just before.
Are you talking about the gas gauge or the range gauge here, or both?
Shouldn't both gauges be calibrated to account for the shape of the tank?
In the paragraph above, I am talking about the fuel gauge.
I think that the people who are confused by the current setup would be even more confused if the gauge display were calibrated to account for the shape of the tank because the scale on the gauge would appear to be random. The gauge is somewhat calibrated to account for the movement of the float on the sender. The top and bottom quarters on the gauge are smaller than the middle quarters.
I don't know why you say that.
Seems to me that linearity would be better than nonlinearity.
How would linearity "appear to be random?"
Not sure what you mean here. Are you saying that means that when the fuel gauge reads 1/4 of a tank, that there's actually less than 1/4 of a tank of gas in your car?
I'll look more closely. But at the beginning, at fillup. the dte is too low. It should tell me about 584 kms. But last time said 503 km to empty. When the reserve gets waaay to big, it creates problems of the who thing being ignored. But they will come and bring me gas for free!
Yes, I agree.
I did not say that linearity would appear to be random. I said that the scale on the gauge would appear to be random.
No, the scale on the fuel gauge for the top 1/4 and bottom 1/4 is not the same as the scale for the middle 2 quarters.
To understand why the fuel gauge on the instrument panel moves the way it does, it helps to understand how the fuel sender moves. Think of the socket where your upper arm meets your shoulder as the switch, your hand is the float, and your arm is the connection between the float and the switch. If you stick your arm straight out and raise and lower your hand, your hand's movement is not straight up and down; you hand is moving in an arc, as illustrated by Michelangelo's drawings. In other words, the float's movement is not linear; it moves in an arc but the level of fuel goes up and down horizontally.
Yes, I got the picture from your analogy to the float in the upper part of a toilet.
But I think you're assuming that either:
(a) the fuel gauge must rotate in direct proportion to the "float" device, and/or (b) the only way to get the fuel gauge to be accurate is to distort the geometry of the display.
What I'm saying the that there's a mathematical formula that will convert the relative movement of the float to yield the correct volume of fuel in the tank and that it would be relatively easy to program the fuel gauge for that formula without changing the display. I don't know whether or not the fuel gauge is designed that way, but it seems to me that's the way it should be designed. Otherwise the fuel gauge is not a very accurate instrument.
Yes to a and b.
The fuel sender-fuel gauge is a much simpler setup. Basically, the sender is a rheostat and the gauge is the load in the circuit. A more accurate system would add cost and complexity for little return for the automaker.
Rather than rely on the miles to empty readout, just watch the fuel gauge and watch for the low fuel warning light.
OK. But I'm still curious to know what the error factor is. In other words, when the fuel gas says 1/4, how much gas is really in the tank? And why is there a 50% error factor between the fuel gauge and the range gauge? That's no small difference.
I agree. That's what I do.
The error factor in the "distance remaining" display varies greatly depending on how the vehicle is being driven. There are so many factors that affect the actual distance that the vehicle will travel on a given amount of fuel that IMO, the "distance remaining" figure is pretty useless information. About the only time that the distance remaining figure is meaningful is when the vehicle is cruising at a steady speed with no gear changes.
You can see the efffect of driving style on the distance remaining by cruising at a steady speed, note the distance remaining, then disengage the overdrive and you will see the distance remaining figure drop. Re-engage the overdrive, and the distance remaining figure will actually increase.
You probably have about 2 gallons remaining when the low fuel warning light starts to come on. If you know what your average MPG is, you can guess how far you can travel when the light comes on. For example, I get about 20 MPG so when the light comes on, I figure 40 miles to empty.
Fuel report. The gueage was reading 1/2. And it took 1/2 to fill, volume measuered at the pump. 1/4 mark will be next.
John
I expect it to use the average fuel economy figure in the calculation. It consitantly tells me I will be empty 40 odd kms too soon. Just if it was within 10 at least but 40+ is too much. But yes, I am stuck with it.
I didn't know I had one! In my Audi it came on with 12 litres remaining (within 1/2 litre) as was stated in the book. I would fill it up right away, (lots of close stations) and it really was 12 l remaining.
John
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