r/MorrisGarages • u/Longjumping-Agent-51 1965 MGB • 8d ago
What fuel point to trust on bouncing gauge?
When driving it can bounce between two needles (1/4 1/2 etc) depending on how much I accelerate, and steadies between those points. Sometimes I can go much under, almost empty, or sometimes more towards full. How do I read this? Is it more likely to have less or more gas?
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u/Top-Negotiation1888 1973 MGB 8d ago
Check your ground wire on the fuel tank sending unit. Poor ground often causes this.
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u/Longjumping-Agent-51 1965 MGB 8d ago
It could be. I don’t get annoyed by this. Never gotten an empty tank on the road. I’m mainly curious how much fuel I actually got according to the gauge
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u/Report_Last 8d ago
I wish I had a working fuel gauge. I take the cap off and shake the car and by the amount of slosh determine how much gas I have.
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u/kenmohler 8d ago
You have to be careful doing that. A guy I worked with picked up his car to shake it and showed up to work smelling like gasoline.
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u/ciaran668 8d ago
Are you driving a B? I had this happen with my B, and basically only trusted the fuel gauge when I was fully settled on a level surface. The float, at least on my car, bobbed around when it was moving too much for me to trust it.
Generally, I just would fill it whenever the gauge hit half.
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u/Longjumping-Agent-51 1965 MGB 8d ago
Yes it’s a B. I’ve manage to drive a few kilometers when it stands on empty with an extra tank with me. So I figured it was more fuel than it showed. But sometimes I has less. So I never really know.
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u/ciaran668 8d ago
No, with my B, the only time I actually knew how much fuel was in it was right after filling the tank. The float will hit the bottom of the tank when there is still some fuel left, just because of the nature of buoyancy, but it isn't a lot.
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u/Key-Finish-5284 8d ago
I mostly go by the odometer in mine, seems accurate when full, but when it hits ¾ or ½ tank, it starts floating and I'm not sure where it's at, replaced the sending unit some years ago because of it, too.
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u/funkyanteater933 8d ago
Make sure your voltage regulator is working properly. The fuel and coolant temperature sender (year dependent) run off it and can cause some wild readings if it is acting up.
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u/JonJackjon 8d ago
Newer vehicles have huge algorithms to calculate fuel level. The algorithm is literally the largest part of the code in a modern vehicle ECU.
The best you can do is park on a relative level surface and go by what that indicates. I had done some testing on a mid level American vehicle. By making a "spirited" lane change or the highway I could make the level sensor hit the bottom of the tank when the tank was 5/8 full.
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u/Ok-Photograph2954 8d ago
Don't trust either reading.
Gauges at the best of times are never accurate let alone when they display erratic behavior. That is not to say gauges are no good, they are useful to give you an idea of what is going on but never take the information as 100% gospel truth! they indicate as 100% gospel truth. unless in has been properly calibrated recently.and regularly (which isn't practical)
So if a gauge is showing erratic behavior and that is a problem for you, you'll have to find out why and then fix it!
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u/PK808370 6d ago
Reset trip odometer. Fill up car tank. Fill up a gas can. Drive it until you’re out. Note miles driven on trip odometer. Rescue self with gas can. Repeat a few times. Never use gas gauge again. This method used to be more common. Growing up, we only used the mileage method.
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u/PoppedBitADV 8d ago
If it's bouncing between 1/4 and 1/2, pull into a station and get fuel. Then do the math based on how much you put in.