n00b question: Is your fuel gauge non-linear?

1 gal stays in the tank.
There could be a air bubble in the rubber linings bit but thats huge
Do you have any power at all? Will the battery fully charge?


Posted via the PriusChat mobile app.

 

We often refer to them as “guess gauges” .

This gauge uses previous driving habits to learn the rate of gas decline.

The joy of the Gen2 is the bladder design.

Used to love renting a Gen2 as it would take a lot to move the guess gauge upon returning the car to the rental counter . But you already know that.

But the behavior you’re reporting sounds normal to me .

 

Load of tripe. Chasing goblins where there are none.

Yes, it is common, nothing wrong at all, your gauge is working perfectly fine.

This is nothing unusual in regard to Japanese cars, and is also not peculiar to the Prius. I don't know whether it is a cultural or legislative (or even marketing) thing, but it seems cars of a Japanese origin have some kind of logarithmic or exponential factor when it comes to the fuel gauge. Every single Japanese car I have had has done this where it takes ages for the needle to move to the half way mark and then from half to empty is quite quick.

It amuses me that so many post on PriusChat seem to think that the gauge should read in a linear fashion and that anything else is wrong.

155 miles on the first "pip" is pretty usual.

 

+1 to @Raytheeagle and @dolj. I have never had a vehicle with a linear gas gauge (car or motorcycle). And I've had a few of both in my 64 years. But the Gen 2 Prius is more disconnected from reality than any of them. My '05 would do about 80 miles on the first pip and my wife's '05 would do about 130 on the first pip. And they both got the same gas mileage and held roughly the same amount of gas.

 

I find that the fuel gauge is actually fairly linear, EXCEPT for the first pip. Ok not entirely linear but not too far off, about 85 km per pip for me.

The trick is to imagine that there are 12 pips instead of 10, and that the top two pips are just invisible.

Outside of the US we don't have the internal fuel bladder, and that gives much less variability in the tank capacity and gauge readings. I have consistently found that even from near empty I only need to fill with about 35L to make it read the full 10 pips, even when I know that I could have added at least 42 to 43L (capacity is 45L, but I'm never filling from entirely empty).

The way I visualize it is that the full capacity is actually 12 pips. The first 37 to 38 L (from totally empty) fills the first 10 pips, and the last 7 to 8L fills the last two "invisible" pips. It's an unusual way to look at it I admit, but from this point of view the gauge linearity is really pretty good.

The flexible tank bladder in the US models adds a bit of extra ambiguity as to where exactly full is. But if you can truly get a full tank of fuel into it, then yes you are likely to get two or even three "pips worth" out of the top pip.

I routinely get over 200 km before the first pip drops, and then more like about 80 to 90 km for each subsequent pip.

 

Telling us how many gallons you put in would be better than the mileage driven.
As was said, it is probably normal for that model.

But yes, the gauges on most ALL cars fall slowly at first and then faster toward the end.

 

@uart has a pretty good explanation. I'll just expand on it. I've found the gas gauge pretty linear in all cars I've owned. What you have to understand is that every manufacturer sets a reserve for the top and bottom of the fuel tank. The gauge is only representing a fraction of the capacity of the whole tank. 80% is full as is 100%. 20% is empty as is 0%.

The bottom or last flashing PiP is to keep people from running out of fuel. I usually find 2 gallons when the low indicator flashes.

The top reserve, I suspect is for two reasons. 1. If for whatever reason the fuel does not fill to full, the car will still register full. (Car on an incline or faulty gas nozzle.) The dealer will have fewer complaints. 2. It makes the car look like it gets stellar fuel economy. Drive 100 miles and the tank is still full. No one is going to complain their car is using to little fuel.

And finally just because the gauge is linear in one car doesn't mean it's the same on another car. On my PiP, the first pip goes out it in under 10 miles. On my regular Prius, I get about 100 miles. I suspect, they used the same fuel gauge settings for the PiP as the Prius. Given the Prius has a slightly larger tank, the top reserve on my PiP is now gone. It's not as apparent because I can plug in so every pip is different number of miles. However, on long distance drives, I notice it.

 

As others have said, the gas gauge is definitely non-linear. On mine, with between 7-8 gallons in the tank and temperature between 50-80 degrees Farenheit, for the first 100 miles or so, it has 10 squares. Then, from 100-200 miles, it drops from 10 squares to 5 squares. From 200 miles to 300 miles, it will drop from 5 squares to 2 or 3 squares. Squares 2 & 3 each tend to last between 40-60 miles. I try to fill up the car when I reach 1 square, but it has started blinking once or twice. I haven't gone more than 10 miles on a blinking square, and it seemed it only took around 20 miles for one square to blinking.

The gauge also drains quicker in cold weather. Basically, the thing to keep in mind is fill the car when there is only one square left. You'll eventually learn the intricacies of your gas gauge so you'll be able to better predict it.

 

Yes the first pip can last over 155 miles at 50 MPG. After that they can be <30 miles per pip.
However, that's if you are lucky. Our flex tank has lost some of the flex, or for some other reason, we cannot fill it any more. So now we can only get about 50 miles on the first pip, and we rarely can get more than 7-8 gals in there...lucky to get 6 gals in winter.
So we are lucky to get 300 or so miles per tank these days.

 

OTOH, the previous cars I have owned all had non-linear gauges, my Gen3 Prius gauge is clearly more linear than anything previous. Though subsequently, this household's '14 Forester is just as good.

Gen3 has a 'normal' fuel tank. U.S.-market Gen2s have that pesky rubber bladder, which often makes these issues worse than in other cars.

I.e. (different words, same idea) the top of the gauge is not at the top of the tank, and the bottom of the gauge is not at the bottom of the tank.

This is driven in part by 'customer expectation management'. For the top, this means one can fill a rental car fuel tank 20-40 miles away from drop-off, and it still registers as full when the car is turned in.

For the bottom, this means that when (not if) one draws the short straw of highly variable fuel consumption due to non-average weather, traffic, mountain climb, etc., the driver still gets adequate low fuel warning before safety margins are frittered away. This helps reduce angry calls to Customer Support claiming 'the car said it had enough gas to go that far, so why did it run dry and strand me in the middle on nowhere in horrible conditions?' This doesn't actually stop many drivers from running out of fuel, but it does make more clear that they have no one to blame but themselves.

 

Here in the UK, I’ve managed 200 miles out of the first pip, 350 miles by the time the tank is showing half full, and 575 miles by the time I’m on the last pip, not yet blinking.

I now usually refuel at this point. I don’t wait for it to blink anymore.

Obviously not a linear gauge then. My old Mazda MX-3 did the same thing with its fuel gauge too.


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