Thew fuel gauge on my Jeep is reading funny I think. When I fill it up it will only fill to about 5/8 of a tank. The amount seems right though. About 8 gallons from a 1/8 tank. It would only fill to about 7/8 when I got it back in September. The only thing I can figure is the sender for the gauge but I figure its probably on the pickup inside the tank correct? How would you even determine thats what the problem is without changing it? I know I could run it to empty on the gauge and see if it runs out of gas or I could try to put more in it after it kicks the pump off but neither is good for a vehicle that has an in-tank fuel pump so its not a good idea.

you can pull it out of the tank and see if the float is still attached to the pump. thats the only thing i can think of there could possibley be another way

The vent tube might be clogged up so the gas pump thinks it is full before it really is because there is built up pressure.

Well since it is still functioning I would say the float is still attached. It might be the vent tube like was said above. How do I figure out which one is the vent tube and how do I check it? I would think it is just a rubber line or something right? Can I get to it without dropping the tank?

Is the vent tube the one running the length of the filler neck and goes into the tank next to the filler? Looks like it would be easy to detach and blow out with air to see if its clogged. I was able to force more gas into it by not putting the filler nozzle into it all the way. When I got in it and turned the key on it read 7/8 of a tank, then when I started it the gauge went down to 5/8 of a tank. Dont know what that was, maybe pressure in the tank causing a mis-read that stopped when the pump started pumping gas.