Fuel gauge inaccuracy

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peterc
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Fuel gauge inaccuracy

Post by peterc »

Following the long trip North to Burley for the Roses Tour merely highlighted my ongoing concerns of my fuel gauge inaccuracy.
So far it's been a question of top up the tank at every suitable opportunity just to make sure especially when trying to avoid motorway prices
Despite careful measuring when assembling the tank sender it clearly doesn't give the correct signals.
3/4 on the gauge is just over 1/2 in the tank, 1/2 on the gauge is only a 1/3 in the tank if you get the drift.
I have therefore recently undertaken a full survey of actual fuel in the tank against the gauge reading by starting with a dry tank and filling it 2 litres at a time. ( yes frustratly slow- took all day) At the same time I have recorded the ohms across the sender.
I am now on the verge of buying the Spyida fuel gauge wizard and wondered if anyone roadtested this device.
Peter C
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clive
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Re: Fuel gauge inaccuracy

Post by clive »

As the tank is wider at the top than the bottom the gauge will not be accurate. If the tank is half full by volume then the level of the fuel will be higher than half way up the tank which is why you will get the innaccuracies you describe although I wouldn't have thought it as great as you state. As a traveler of long distances, all I am bothered by is full and quarter, which is when I start looking to refuel. On a long trip such as Silverstone (400 miles) I look to get there on two tanks, although it can be touch and go especially on the way home late at night when there is no fuel stop open between Edinburgh and home.
Cheers, Clive.

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peterc
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Re: Fuel gauge inaccuracy

Post by peterc »

Hi Clive,
Yes, fully appreciate that the tank is tapered but not dramatically. I have of course always been concerned when the gauge gets below 1/4. One benefit of my investigation is that when it gets to zero that I have found I still have 1 gallon left. The change in ohms is very small between a dry tank and 6 litres but I will ask Spyida how easy it is to set their system that accurately.
Do I assume that you continue to ignore the gauge errors and just fill up on mileage/ 1/4 gauge. Whilst I can get over 20 mpg if I don't boot it, the A43 as a typical A road with roundabouts soon lowers the average mpg. To date I haven't dared go too far below 1/4 as I have not know the exact capacity. I always assume it was 10 gallons but now know it's 49.5 litres ( 10.88) to the bottom of my filler ( remembering mine is an FIA with the filler at an angle)
Yes, I have lived with the issue for over a decade but having found a potential solution thought I ought to have a go at correcting it and make the gauge speak the truth.
Peter C
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clive
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Re: Fuel gauge inaccuracy

Post by clive »

Hi Peter,
When I first built my car I had issues with my all my electrical gauges under-reading and I checked all the usual suspects such as earths etc. When tanked up, the fuel gauge would show just over 3/4 full and when it showed empty there was still about a quarter tank left. This was resolved after my Le Mans trip in 2010 when I had fuel pump issues. Because I was blowing fuses with great regularity and it was difficult to find the canoe type fuses for the Hawk supplied fusebox, I changed it for a small blade type fusebox and the difference in all the electrics was amazing.
Normally I won't let the tank get too low, but I have on occasions seen the gauge get to just off the empty and it was a twitchy experience. I do carry a spare gallon can on long runs though just as insurance, especially if I'm travelling late at night or on a long trip such as Silverstone as you just don't know where the nearest petrol station is. Needless to say in over 40k miles in the 289 I've never needed it.
Cheers, Clive.

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Roger King
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Re: Fuel gauge inaccuracy

Post by Roger King »

Come on chaps - it's a sixties design. Full on left hand bends, empty on right. Once it stops moving you're in trouble.
I set the trip at every fill-up. When it gets to 160, I start looking for fuel.
DavidP
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Re: Fuel gauge inaccuracy

Post by DavidP »

I follow the same practice as Roger and a full 5 litre can in the boot - just in case....
SiJackson
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Re: Fuel gauge inaccuracy

Post by SiJackson »

And how far does that five litre can get you? Fuel stations are few and far between up here. That can would just postpone the misery for another 20 minutes :D
DavidP
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Re: Fuel gauge inaccuracy

Post by DavidP »

....not very far - but it's a comfort thing!!!!...
monster7
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Re: Fuel gauge inaccuracy

Post by monster7 »

I had the same problem with my fuel gauge.
I first checked if the sending unit operates in the same ohm range as the gauge! This was ok, but the gauge shows still 1/3 if the tank was already empty. So i called the tech support and they told me that behind a little sticker in the gauge case there is a very little Poti to adjust the gauge! I didn't know that.
So i measured the fuel level in the tank and then adjusted the gauge properly...i now have a accuracy of approx 5% :).

PS: my gauges are from MotoMeter/VDO W.Germany and 20 years old
Kind regards, Ronald
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peterc
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Re: Fuel gauge inaccuracy

Post by peterc »

Many thanks for your replies guys.
So it seems no one has bothered to correct their gauge apart from monster who has VDO gauges with it appears built in adjustment.
I have never noticed any fuel gauge surge on corners but then I am probably too busy driving. I too reset my trip at every fill up an use the miles as an indicator to fill up at 150 miles. The issue is that the mpg can vary a fair bit so I would have to remember how often I have enjoyed a bit of acceleration ( read most roundabout exits )
I am not worried about the full condition reading way over 4/4 on the gauge but it would be nice to know what is really happening below 1/4 full on the gauge before running on fumes.
It looks like the gauge becomes a bit more accurate around 1/4 which is nice to know with approx 11 litres left so I might just continue to fill up then or at 150 miles whichever is comes first.
I am still tempted to have it read better throughout now that the technology is available. After all I now have LED rear lights and dash board lighting.
Peter C
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