Is there a digital readout gas gauge so that when I am driving down the road I can see exactly how much fuel is in the tank
An accurate reading of fuel in your tank has nothing to do with an analog or digital gauge. It’s all about the sensor in your tank. Fill it when it hits 1/4 tank and don’t run out.
No. Maybe. Why would we need one? What we need is a gauge that can text us the exact amount so that we will notice it.
Not for motor vehicles. The sender in a gas tank is a variable resistor that is crudely calibrated. The variable resistor is positioned by a float. The gas tank typically has an irregular shape which does not help with accuracy; makes sender voltage linearity worse. A much more accurate setup would require a tank that has a regular shape or else a small computer that could modify the voltage reading from the sender to reflect the irregularity of the tank shape plus the sender’s resistor value change due to temperature change. It would all cost more money than what most would be willing to pay when all you really need is a crude indicator as it is now.
Newer cars have a gas mileage computer, if that is what you are after, that is fairly accurate; within about 5% is my estimate.
Some luxury cars of the '80s had something like this (like my friend’s '83 Cadillac Seville, which tells you how many gallons you supposedly have left), but it was the same old system with some new, gimmicky stuff attached to it. A precisely calibrated system like this would be impractical, if not impossible. One problem is that a car tends to move because people tend to drive them. Fuel sloshes around, making it impossible for any reasonable, non-lab-grade method of measurement to work effectively. The best way to know how much gas is in your tank is to do two things. First, get into the habit of filling the tank before you are in danger of running out. Second, reset your trip odometer each time you fill up so you know how far you can drive on a given amount of gas. An added benefit of this habit is that any notable change in gas mileage will be noticed right away, and any discrepancy in the fuel gauge accuracy will also be noticed right away. For example, if you previously had to fill up every 300 miles, but suddenly have 350 miles on half a tank of gas, something’s wrong, probably with the fuel gauge. I have been doing this for years, never had a problem, never run out of gas, and so far have never noted a problem by using this method, but still do it anyway for these reasons.
It’s not impossible, but it would be expensive. You’d need a multi-capacitance sensor system like they use on commercial aircraft. Such expense would be silly for a car.
You’d need four sensors (one in each corner) that operate the full range of the tank (dead empty to topped off full), some way to average the signal, and some way to generate a compensation curve to compensate for the fact that the tank is an irregular shape.
One, the gas stays level to gravity, not to your car. If you’re going uphill, it collects toward the rear of the tank, down hill it collects toward the front.
Two, there’s centrifugal force to consider. Unless you live in North Dakota. There are no curves in North Dakota. Actually, there are no hills either.
Three, agitated fluids take up more space than fluids at rest. The mass stays the same, but the volume changes. Which would you like?
Forth is the irregular shape. The tank has irregularities to go around the axle, the exhaust, stuff like that. A compensation curve would have to be created to compensate. To illustrate with an extreme example, think of a sailing sloop. One foot down from the waterlilne displaces a great deal more water than one foot down from the place where the hull bottom turns to keel.