Fuel gauge
 

I have had the truck since June and have been working on getting it driveable since then, one of the things puzzling me is after driving for about 20 minutes, the gauge would drop to empty no matter how much gas I had. I could get it back if I released the pressure in the gas tank by opening the cap. Last weekend I changed the spark plugs, the old ones were all dirty and gapped probably twice as far as .44, and one of them was bridged across to the electrode. This weekend I went to the cottage and back with the gauge working fine the entire way. I don't need to fix anything I am just curious as to why this had happened.
Thank you
Tim

Re: Fuel gauge
 

I would try disconnecting the lines to the evaporative canister and see what happens - it could be clogged.

Re: Fuel gauge
 

Actually there is nothing going to the canister, I know this truck was a c10 put on 4x4 frame before I got it. It is a 1975 truck, did they have evap canisters?
Thank you for the reply