How does a fuel gauge work when driving when the fuel is shaking?
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most fuel tanks have baffles in them to minimize sloshing of the fuel and help reduce fluctuations in gauge readings…gauges that work on electrical resistance also do not react immediately, taking several seconds to register changes
if you drive up a long hill, or on some stretch of road that alters the level of the float in the tank, it will eventually change reading on the gauge
There are several ways, but it depends on the car.
Most cars use a float in the tank, which attaches to a resistor track by an arm. In some cars there’s also a “damper pot” filled with fuel from the tank which slows down movement of the float when the car moves.
Then, the fuel guage needle,which whether it’s a physical needle or not, is electronically controlled. That electronic control has another damping in the signal before the fuel needle moves.
Cars can also cross reference the float reading from the tank with the amount of fuel injected since last refuel to better estimate remaining fuel level.
I’m not sure why someone else has said fuel tanks have baffles. They don’t. It at least none that I ever saw in several years designing fuel tanks
EDIT: so apparently damper pots are called baffles in North America. Every day is a learning day!
Older fuel gauges have a buffer module that acts to “smooth” the signal to avoid fluctuations due to fuel slosh. Many classic cars have no buffer whatsoever, and operate on simple resistance at the sending unit. On those, you’ll see the needle move on the gauge quite frequently.
Newer gauges which communicate with an ECU have a running table of values, so the fuel sender signal data is recorded at some interval. The table of values is averaged, so an outlier value gets “lost in averages.” If you have high and low values from sloshing, they’ll average to the true level with enough data points. As the newest data point enters the table, the oldest data point is purged.
Plus, some modern fuel tanks are designed with baffles, specific shapes, or split in the vehicle’s frame/body to help eliminate unnecessary sloshing and aeration. Aeration in fuel (bubbles) is not a good thing in any metered system because air is compressible, compressed air builds heat, and the change in volume and throws off metering (like opening a bag of potato chips and seeing that it’s mostly air).
The gauges a slow to respond to change, so they effectively give you they average reading over 20-30 seconds. The gas might slosh about, and the little float go up and down, but it will stay centered on the average level (some tanks have little walls inside to make it slosh less). the only time you might see it change is when you are on a hill and the gas isn’t sloshing but settles towards one side of the tank – that will often cause the gauge to drift up or down.
There is software damping and averaging in the dashboard, so it’ll take readings all the time, but average out any sloshing.
I’ve even seen coding and configuration data in some dashboard software for refueling detection, when it will figure out you’ve just refueled, and it will forget about the damping for a short while to account for a rapid increase in fuel level.
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Anti-slosh module. Takes the signal from the potentiometer of the fuel level sender, and electrically smooths and slows the output that is displayed by the dash. Now done digitally by a digital dash.
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