Non linear fuel gauge question
Discussion
I’m sure this has been mentioned before, so sorry if I am repeating an old thread.
I started driving in the mid 80’s. Most of the cars I drove were from the mid 70’s. From then, u til about I started getting cars from the early 2000’s, the fuel gauge was broadly linear - as in, if a full tank did 400m, at 100m it was showing a quarter full.
Ever since then, every single car I’ve driven from a full tank, the needle doesn’t budge until at least 50 miles, and often closer to 100, after which it plummets.
Any ideas why?
P.S. don’t get me started on oil pressure gauges like the MX-5 NC, where the ‘brain’ says ‘well I’m doing x revs in gear y, therefore oil pressure must be z’. But the fuel gauge issue seems to be a reverse of that ‘logic’?
I started driving in the mid 80’s. Most of the cars I drove were from the mid 70’s. From then, u til about I started getting cars from the early 2000’s, the fuel gauge was broadly linear - as in, if a full tank did 400m, at 100m it was showing a quarter full.
Ever since then, every single car I’ve driven from a full tank, the needle doesn’t budge until at least 50 miles, and often closer to 100, after which it plummets.
Any ideas why?
P.S. don’t get me started on oil pressure gauges like the MX-5 NC, where the ‘brain’ says ‘well I’m doing x revs in gear y, therefore oil pressure must be z’. But the fuel gauge issue seems to be a reverse of that ‘logic’?
KillerHERTZ said:
Fuel tanks arent a uniform size, some have smaller sections at the bottom with larger at the top, thus taking longer to empty the first 'half' than the smaller lower section.
Good point which I hadn’t considered. Ok, but I think that with modern tech and odd shaped tanks it wouldn t be the work of a genius to figure some way of doing it.My first car - a 1947 Ford 10 - had a very erratic fuel gauge. Depending whether the car was pointing uphill or downhill, it showed either half-full or quarter-full. On the move, the needle would dance about merrily giving no real clue as to the contents.
My current two-wheeler is a good example of what the OP describes. I now know that it has a range of about 180 miles, but when I first got it I filled it up and the gauge showed 'F' for 150 miles before dropping to three-quarters. Alarmingly, only 10 miles later it was down to half, then quarter and empty, at which point the fuel light came on and the gauge was blank! Being in the middle of nowhere, I discovered it would do 10 miles showing empty.
So, 30 miles from full to (apparently) bone dry.
My current two-wheeler is a good example of what the OP describes. I now know that it has a range of about 180 miles, but when I first got it I filled it up and the gauge showed 'F' for 150 miles before dropping to three-quarters. Alarmingly, only 10 miles later it was down to half, then quarter and empty, at which point the fuel light came on and the gauge was blank! Being in the middle of nowhere, I discovered it would do 10 miles showing empty.
So, 30 miles from full to (apparently) bone dry.
Yeah I used to have a Chevvy C10 pickup which had a fuel tank that was literally a massive box with a sender unit that would bounce up and down with the fuel, and send that sloshing information directly to the fuel tank gauge in the dash.
No dividers in the tank to stop the sloshing. No computers that would measure the tank capacity and average out the readings to provide a useful measurement like modern cars.
And with a carbed 5.7l V8 engine, knowing how much fuel you had was fairly critical information.
The only way you could really tell it was empty was when the needle was at E and wasn't moving anymore...i.e. there wasn't any fuel to push the sender around anymore.
We've come a long way...
No dividers in the tank to stop the sloshing. No computers that would measure the tank capacity and average out the readings to provide a useful measurement like modern cars.
And with a carbed 5.7l V8 engine, knowing how much fuel you had was fairly critical information.
The only way you could really tell it was empty was when the needle was at E and wasn't moving anymore...i.e. there wasn't any fuel to push the sender around anymore.
We've come a long way...
sasquartch said:
Most cars have some sort of 'miles of range remaining' so the fuel gauge isnt so important these days
I find it quite funny that when the computer runs downto zero on my Octavia,there are still 60 miles of fuel left. Which means you can do 100-120 miles
on yellow light. More if you start slipstreaming lorries ;->
A few people have been confused by the computer saying there is no fuel left,
then putting in half a tank (25 litres) and getting a fuel reading of 5/8 of a tank.
Either that or Skoda know their customers are a bit "careful" on the fuel front.
paradigital said:
I m sure I ve read that it was a conscious decision to appease the psychology of most customers.
The fact that the needle or gauge moves slower after first filling up makes people less annoyed/upset than if it were linear.
I have to admit that was my suspicion.The fact that the needle or gauge moves slower after first filling up makes people less annoyed/upset than if it were linear.
I’m also surprised that modern cars fuel level is still measure by a simple float, I’d assumed there must be some form of tech that could work it out, including with an irregularly shaped tank.
I am driving my 1982 van as a daily at the moment (DS3 off the road for airbag recall).
The fuel gauge is wild. It never sits still for more than 30 seconds and can swing by 1/4 of a tank.
I 'sort of' get used to it as I have owned the van for 14 years. But I do sometimes wonder whether they can enfrom the factory like that???
The fuel gauge is wild. It never sits still for more than 30 seconds and can swing by 1/4 of a tank.
I 'sort of' get used to it as I have owned the van for 14 years. But I do sometimes wonder whether they can enfrom the factory like that???
Fuel gauge readings are heavily electronically mediated these days, that's for sure.
Back when you got a direct reading from the tank sender, with just a bit of delay built in to the gauge mechanism, the needle moved about a lot more. The gauges in my mum's old Minis used to move driving up a long hill, or even parked with one wheel on the curb.
That's the kind of uncertain but accurate reflection of reality that we don't seem to like any more. Better a smooth and reassuring lie than the messy truth;)
Back when you got a direct reading from the tank sender, with just a bit of delay built in to the gauge mechanism, the needle moved about a lot more. The gauges in my mum's old Minis used to move driving up a long hill, or even parked with one wheel on the curb.
That's the kind of uncertain but accurate reflection of reality that we don't seem to like any more. Better a smooth and reassuring lie than the messy truth;)
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