Fuel Gauge Theory

So far I get the impression my fuel bars are more consistent than when the last bar
starts blinking.

From my last bar to the blink I've seen as little as 10 miles and as much as 50.

 

I have tried to tie the bars to gallons used between bars. I could only do it for the 1st 1/2 tank. There seems to be some deviation between bars.

I figured it out this way:
Wait until first bar goes away. Calculate gallons used by dividing MPG/miles.
On next bar going away, do same. This is total gallons used since fillup, so subtract last calculation.
Repeat for each bar.
This will allow for gallons per fillup and MPG variations.

I have noted though, on the average, the 1st half tank bars are about 30 miles apart, except for full to first bar, which is about 170 miles.
Last half of tank is about 50 miles per bar.

 

Actually the fuel gauge is pretty accurate, at least in my Classic, but because we drive it in different conditions and that make it seems inaccurate.

First we need to understand how the meter ECU corrects the calculation of fuel level:

1) 2 inclination sensors that detect the vehicles's longitudinal and latitudinal inclinations.

2) An ambient temperature sensor in the fuel tank to detect the temperature in the fuel tank.

The fuel level is calculated by the meter ECU in accordance with the signals of the sender gauge located in the sub tank, and the vehicle speed signal received from the skid control ECU. At this time, corrections are made by the signals from the inclination sensors and the ambient temperature sensor.

So, if we do not always travel on level road and the temperature swing is huge, how can we expect the bar to bar transistions to be linear? Beside this, there is also the "bladder" effect that adds to the complication.

For my case, even without the "bladder" and our roads are almost flat, I can notice the effect of temperature on the fuel level. My commute are mostly going to work early in the morning and going home late in the evening. Temp. range from 26C ~ 30C and the bar to bar transistions are almost linear from the 9th bar to the 3rd bar. 10th bar depends on how much I topped up. 2nd bar and 1st bar drop very fast. Blinking bar is the same as those in the 9th to 3rd bar. However, in the weekends, if I drive on hot afternoon, normally 33C ~ 36C, the fuel level will drop much faster. Since the fuel gauge uses resistive element, higher temperature will mean higher resistor value and higher resistor value means more empty.

I'm sure everyone must have seen this, the fuel level just dropped 1 bar before you switched off the car. On the next morning, the fuel level gain back 1 bar.

Vincent

 

I have been tracking the current miles and computer MPG for each bar. Of course I don't always catch when a bar drops. But, it seems that for 6 bars and lower, the number of miles between bars tracks kind of closely to the computer MPG at that point in time.

From full to 6 bars seems much more variable. For example, my last tank with computer MPGs mostly 39+, with about 41 for the first 3:

 

I average 46-48 MPG on the tank, and my fuel gauge starts to blink anywhere between 320-360 miles. If I fill up when it tells me, I can barely fit 8 gallons in there. I now ignore it and fill up at 400 miles, and I've still rarely made to 9 gallons needed to fill.

 

I think it is more like the Australian's version because when I DIY CC, there was also no Cruise Light Indicator.

 

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Due to high import tax, many items, that are standard in other countries, are removed in the SG ver., eg. NAV, CC, Alarm, etc. In spite of this, it still cost more than 3X (USD 63K) as compared to other countries. :guns:

Vincent

 

$63,000 for a classic? Or even an '05? What do other cars cost? Much as I love my Prius, I wouldn't pay $63K for it!!!!

Public transportation here I come!

 

As this thread has drifted from original post, I 've created another thread in the International Owners.

Prius in Singapore

Vincent