toyota gas gauges

Yep,my Tacoma does the same thing. Takes almost 200 miles to get from full to 1/2, then only 90 to 100 more to empty. Scott

Exactly the same with my 96 Tacoma.

I think they're all (as in not just Toyota) similar. Seems the gage senders are linear when the need is logarithmic. Since the sender is connected to the ECU in all/most modern cars/trucks, the issue could be corrected in software. My guess is that makers don't consider this an issue because not enough customers have complained. As a practical matter, once you're accustomed to a particular vehicle's gage characteristics, it usually does become a non-issue.

What do you mean, "the need is logarithmic"?

The gauge in my Prius (2005 model) does not behave that way; but it may be an example of the coming wave of technology. (See, for example, how the Prius ignition key system seems to have been put into the Yaris -- if I read the ads right. Ideas move around.)

This gauge shows eight (8) rectangular segments in a row, where "all lit" means "45 litres", 5.625 litres per segment. To this can be added a cup in the filler pipe, which of course the gauge officially cannot "know" about.

A couple of days ago, after traversing the UK A684 from Kendal to the A1 (details for folks familiar with UK roads -- basically the Yorkshire Dales around "Herriott Country"), I had to put in 40.01 litres to fill it to the brim after the last segment had been lit for maybe five miles. Over that twisty, winding road I was doing

'91 Celica GT-Four. Although im never sure if its just the car being lighter and more nimble makes me want to give it some more right hoof later in the tank :D

Surely the need isnt logarithmic, the need is a gauge that reads linearly as the sender does? Your fuel doesnt vary logarithmically. Mine you my tank does have a narrower squeezed section in the lower half (approx 2/3 of the upper halfs volume) so that does explain a lot. Only time you'd need logarithmic senders is if you have a very strangely designed tank lol.

I doubt the sender output is linear but rather skewed in an attempt at matching the physical characteristics of the tank - quite probably in a logarithmic way. Making linear reading digital or analog gages is a snap. The sender's the problem. Or, one could use a linear sender, then correct it's output via software as I originally suggested. This would have the added advantage of being inexpensively varied via an ECU flash if production tanks or other parameters change.

Mine is linear, ive had it out to check several times :-) But even so logarithmic output wouldnt match the tank shape, it would have to be a custom output profile unless your remaining volume varied logarithmically also, not likely in a strange shape of tank that is designed so fits around the rear axle and exhaust areas, not so the gauge reads right :)

Which is the easy way out, but on a 1991 this is not the case - hence my explanation of the tank shape. But yes, modern software controlled gauges should be easy enough to calibrate.

Incidentally my fathers BMW gauge reads perfectly, and thats a '91 also. Quite annoying.

this is done so when the tank reads empty you have a little gas in the tank. on my 06 camry when the gage reads one half tank it will take 9 gal. which is about right. ( 18.5 gal tank) one half of 18.5 is 9.25 gal. but when gage says empty it will take 16 gal to fill. which means there is still 2 and a half gal in the tank when it should be dry. so full to one half 9 gal. and one half to empty 7 gal. so 9 + 7 plus 2 and a hale = 18.5 gal. do you really want a gage that when it says empty empty is really empty? lots of people would be running out of gas. when you fill up you car the gage goes above the full mark. i can drive 50 to 60 miles around town before the gage drops to the full mark. but the tank can not really still be full. the gage just gives you a general idea of how much gas you have in the tank. so you don't run out.that is as bad as complaining because your car has a 140 mph speed o meter and it will only do 110 mph. good god.

The reason for the way the gas gauges operate is very simple. It has nothing to do with algorithms, logarithms, ECU's, or fuel mileage.

The fuel sender operates much like the fill valve in a toilet tank. There is a float mounted on an arm, and the arm moves up and down with the fuel level in the tank. As the arm moves up, more voltage is passed to the fuel gauge and the needle rises on the gauge. The shape of the fuel tank is not symmetrical so there is some inaccuracy caused by the shape of the tank. Also, the float's movement is not vertical - it moves in an arc while the fuel level moves vertically so movement is exaggerated in the middle of the arc's movement.

If they actually put enough effort into the sender to make it send skewed values, I would expect the result to come close to actual values. Since this isn't the case, I doubt that they actually took the time to make the sender send data in a logarithmic way.

Just because the guage displays that it's empty when it's actually not doesn't mean that it prevents people from running out of gas. People adjust. I know that my guage can go lower than the empty line so I let it. If I knew that it was actually empty when it got to the line, I would fill up before that. I tend to want my guages to be accurate. Would you be fine with your speedo if it showed 60mph when you were actually going 90mph?

Your reasoning is silly. I want a speedometer that is fairly accurate so I won't get a speeding ticket. I want a gas gauge that is fairly accurate so I can determine when to fill up, not when someone else thinks I should.

Your reasoning is similar to a conspiracy theory. Let's give them this information and they will think this, but the real answer is they have more than they think they do. No, I think it is more of a mechanical issue.

So just how close to E The big empty can one safely go? Some cars - if it floats it is ok. Other start having a 'jumping needle' at empty. My GM is empty at 1/2 full indication. Just stop for a few moments at an out of fuel emergency stop and you are good for another 10 miles.

Makes for exiting driving!

When the low fuel indicator light comes on, I assume that there is 1 gallon left (there is probably more than 1 gallon). Multiply 1 gallon times the mile per gallon you get in the city and you have the distance you can go before you run out of fuel.

So you assume one gal left - and further one gal of usable fuel. Anybody ever try this? My experience (GM mainly) with indicator lights has been pretty negative! Useless and after the fact. j

There is more than 1 gallon of useable fuel left in the tank when the low fuel indicator light comes on. Using the city fuel consumption, i.e., 17 mpg, gives you plenty of reserve. You can probably drive closer to 40 miles with the light on, if you assume that you can only travel 17 miles, you have given yourself a cushion of 23 miles.

If you don't trust me, fill up the tank as soon as the low fuel light comes on and note how many gallons it takes to fill the tank, and subtract that number from the tank's capacity and you will know how many gallons were remaining in the fuel tank when the light came on. There is probably 3 or 4 gallons.