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After my new fuel gauge went bonky, I installed my old fuel gauge that was in my truck when I bought it. I had a decal sheet for the gauges so, I have a nice-looking original fuel gauge. My gas tank was not full, so my gauge read just over half a tank. I learned that it is absolutely necessary to have a dedicated ground to the sender unit. Without it, the old gauge and the new one I had, were not steady, the needles bounced around a little because of the resistance to ground. Once I put a dedicated ground wire on my sending unit the old gauge is steady. I went for a drive today and ended up filling up the gas tank. The needle went to the dot just below the F. The center dot says 1/2, and the third dot is just above the E.
MY question is: Where do most people's gauges run? By my calculations I had 1/4 tank in my truck. The gauge was halfway between the 1/2 and the bottom dot. Which would be 1/4th of a tank, (if the bottom dot is empty) and the top dot is full that would be correct. I put in 12 gallons, and I have a 16-gallon tank. Do your gas gauges stay between the three dots? I don't have any experience with the truck having a gas gauge that works. I have not had it on the road that long and the new gauge quit soon after I started driving it. I just kept a record of my mileage because I could not trust the gauge.

That's funny. I asked the same question a couple years ago after installing a new tank and sending unit.

Mine also goes to the dot just below "F" when filled up to into the filler neck.

When my gauge first touches "E" I have determined that there is about 4-5 gallons left. I keep track of my fuel economy and mileage so I can estimate how far I can drive on a full tank of 18 gallons.

I always fill up when the needle get below the halfway mark.

I discovered that issue awhile back. Logic would be the tank is full on the F empty on the E but on my truck that is not the case. Mine is empty at the dot near the E and full at the dot near the full. Here is a thread on this subject. https://www.stovebolt.com/ubbthread...you-to-46chevypu-s-wife.html#Post1510467

What I have learned over the years in the HVAC trade is that gauges are designed to be most accurate at mid gauge. With that in mind, when I replaced the gas tank, sending unit, and the wire between the tank and gauge, I started with an empty tank, added a measured 9 gallons of gas, adjusted the sending unit arm/float to read 1/2 tank on the gauge. Whatever the high and low readings are will have to do.

Mine runs true to E, mid point and F but what I've learned is it pretty much depends on the accuracy of the sender. The AD fuel gauge was a very good one and will be accurate as long as it receives resistance of 0 ohms at empty, 15 ohms at mid point and 30 ohms at full...unless something wonky is going on like the needle is bent and rubbing somewhere. What I've also learned (and it took m almost a year's worth of studying this) is that the fuel gauge senders being sold out there range from mediocre to absolute junk. There's one sending unit I like a lot...have mentioned it here often...it is sold on eBay by a seller whose id is renbusan. About $30 shipped and is very accurate. It was designed and made in Taiwan by somebody who knew what they were doing. Good luck!

I guess I’ve got some work to do. LOL!