It hs only happened twice, once last Fall and again today.

I left for work this am, and noticed gauge was on empty, yesterday I drove it and gauge was half full.


Of course I though punks had siphoned my gas last night, so I cursed and pulled into gas station, I wasn't going to fill it to again have it get siphoned, so I put in 6 gallons.
I left the station, and now the gauge reads ALMOST FULL!

Turned of the truck and started it again, almost full again, so yesterdays half full reading was correct.

What can be causing this?

 

A bad float, a bad sending unit, or a wiring fault are the most likely causes. A bad float usually manifests as a gauge that reads correctly only for a short time after refilling the tank from very near empty. A bad sender or a wiring error seems more likely for you. Time to break out the DVM and get to troubleshooting.

 

there is also a ceramic tab that detects engine level. THat gets corroded and causes the gauge to read "haywire." It took about a year of using fuel treatment to get that fixed. Or you can just replace the fuel pump/ the ceramic tab is on that whole unit.