Fuel gage non-linearity

[viking31]

OK, I’ll make this the 3,001 thread regarding fuel gage issues. I am on my second fill up now and have noted, as stated in other previous threads, the fuel gage is indeed not very linear in stating the amount of fuel remaining.

But has anyone addressed as to WHY this is the case? Perhaps this would have been acceptable 10 or 20 years ago but it seems that the Toyota engineer who designed the fuel readout could have simply programmed 50 or 100 data points into the fuel gage algorithm (assuming it is software driven) to give a more accurate reading on the amount of fuel actually left.

I typically use about 2.5 to 3 gallons of fuel before it moves just one block on the gage.

Perhaps it was done intentionally (Wow!, look honey, see how little gas we used for the first 150 miles and the gage has hardly moved!!)? Or was it a cost saving measure? There might be a hundred other “little” issues that if addressed could put the cost of the Prius out of the planned final cost the bean counters mandated. This may have been one of them.

Not a big deal and I won’t be running out of gas on the freeway soon because of the non-linearity of the gage, but…

Rick

06 #4 silver, West Central FL

[geologyrox]

Toyota has been doing this for quite a while - my husband's Celica is exactly the same. The first bar, as well as the last bar, both last a lot longer than they should. The next few last a bit longer, and then it seems linear in the middle.

I'm not sure why they've decided that they want you to actually have 3/4 of a tank at -1 or -2 bars, and 1/4 of a tank at the opposite end, but it's definately by design. My husband thinks it keeps him from running out of gas, but since neither of us have ever done that in any car, I find it hard to believe that's actually why they'd do it.

[OUscarb]

My 02 Tahoe and 04 Avalanche did the same thing. Not just Toyota.

[viking31]

Originally posted by geologyrox@Jan 23 2006, 09:28 AM
My husband thinks it keeps him from running out of gas, but since neither of us have ever done that in any car, I find it hard to believe that's actually why they'd do it.

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I am leaning to believing that it is intentional and perhaps does help SOME people not to run out of fuel.

And I have read some pretty testy exchanges recently regarding “who” gets fed first.

For the record, I feed my Prius first, THEN the wife and kids. The Prius just quits when it runs out of food, but the others only complain…;-).

Rick

[Spunky]

Originally posted by viking31@Jan 23 2006, 09:45 AM


And I have read some pretty testy exchanges recently regarding “who” gets fed first.

For the record, I feed my Prius first, THEN the wife and kids. The Prius just quits when it runs out of food, but the others only complain…;-).

Rick

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The Prius gas tank is lined with a vapor-limiting bladder. That might well lead to the non-linear problem you've noticed.

[windstrings]

Originally posted by Spunky@Jan 23 2006, 06:48 AM


The Prius gas tank is lined with a vapor-limiting bladder. That might well lead to the non-linear problem you've noticed.

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Looks like they could shape the tank in such a fashion to promote a more linear drain... even if it was a hassle to do it electronically.

[viking31]

I just found this off another newsgroup. I think I am starting to answer my own question and it IS what I am becoming to suspect. The original thread from the quote below started on how some people actually believe that a car gets better mileage when the tank is more than half full. Some people are so clueless (I am not saying they are "dumb" per se, they are just "turn the key (or push the button for the Prius!) and go" drivers) on how and automobile works that they actually believe this stuff.

It is also a known fact that from the 1950s to the 1980s, maybe later too, car companies engineered fuel gauges to stay longer at the top of the gauge, with the intent being to give new car buyers a "warm fuzzy" about how great their new car was doing on gas mileage, so they could pass on word of mouth to their friends. That's true.

The above explanation now seems very feasible to me...

However, I even remember catching myself "bragging" the above to my friends on the first tank. I KNEW how much fuel I actually used but the fuel gage says...

And I am well aware of the bladder of the Prius and its purpose but I don't see how the bladder would affect the LEVEL of the fuel at any given time.


Rick

[Betelgeuse]

Originally posted by viking31@Jan 23 2006, 10:16 AM
The original thread from the quote below started on how some people actually believe that a car gets better mileage when the tank is more than half full.

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So, I certainly don't believe that the car gets better mileage when the tank is more than half full. HOWEVER, wasn't there some discussion on this board a while back about how you should keep your tank more than 1/4 full? Something about the cooling of the in-tank fuel pump? Now, it seems a little dangerous to me that you'd be using gasoline to transfer heat, but I guess that if there's not significant oxygen in the tank then you wouldn't have to worry about it?

Just something I read; I may be off base.

[SomervillePrius]

I saw a similar post here about tanks last week. Someone posted a picture of a modern gas tank and it's not a cylinder anymore but a very oddly shaped container meant to squeeze in in a tight space. I suspect this makes the meter be none linear as well. I also think they have a very simple meter in the tank and don't get a good reading.... so to compensate I'm sure they make it look full longer then drop fast...

My maxima does the same not sure what the big deal is... All I use the meter for is for a quick look to see if I need to fill it up right now. I'm not surw I want engineers to spend a lot of time on making the meter linear. I would rather have them spend time on real FE issues or maybe improve the seats

[windstrings]

Why not improve the digital meter?

Providing you start off with a full gas tank:
Why can't the car tell you have many gallons you have used and how much left?

If the car already knows:
1. when you fill the tank
2. Consumption of gallons used "it knows exact mpg?"

There is complaint about the guage not being linear.... why can't it just show you how much is left and how much you have used?

And for those instances when you don't fill all the way to the top, you could add an entry.