Rusty fuel cap

[rtadams89]

My fuel cap looked lose so I went to tighten it and the insides disintegrated when I went to turn it. The entire inside was pretty much rusted away. I don't think there is an appreciable amount of water in the tank, as I have used both a PIG water absorber and have recently pumped out the corners of the tank and neither reviled any obvious water. Mu assumption is that there is just moisture in the air in the tank, which is causing the gas cap to rust. Right now, I'm at about 3/4 tank of diesel, so there is a littler more air space in there, but even full I only fill it up to the fill line which leaves some air space for expansion. The in tank pump supports don't look rusty, and other than the fuel cap itself, only the very rim of the tank neck has any signs of rust.

I live in AZ, and there is no rain expected in the near future; should i just leave the fuel cap off for a few days to get some dry air circulating in there? Other ideas or things I should check?

 

[SCSG-G4]

Fuel tank caps and the rubber seal are available from our sponsor vendors. You can always put heavy plastic on the opening and them put the cap back on just to keep trash out. I would NOT leave the cap off overnight, as there is always some moisture and it will precipitate on the cold surface of the tank.

 

[rtadams89]

I have some new caps on the way from Big Mike. My concern is, what is causing the rust? Mosture in the air in the tank? How do I get that out to prevent rust going forward?

 

[peashooter]

I dont have an answer to your question but have heard of some folks coating the inside of the tanks with something (dont recall what) that is intended for this. Also the m35a3 trucks have aluminum fuel tanks so you could always look for one of them.

 

[WillWagner]

It rusts at the cap and top of the tank because that is the high spot and condensation goes to the high spot. Condensation happens because there is warm/hot fuel returning to the tank, and in your case, high ambient temps. When the outside air temp drops, the fuel stays warm longer and creates condensation. This is and has been an issue with diesel powered, and gas powered things forever. The tank on your deuce is not vented IIRC because of the fording capability. You can remove the fording line and make it a vent, or get a vented cap. This will help.

 

[rtadams89]

The stock caps have a vented and unvented position. Mine have been in the vented. I'm going to head to the truck tomorrow and use a transfer pump to suck out the bottom inch or so of fuel (and hopefully water) from the tank. Then I'm going to scrub out the rust from the filler neck, while catching the crap as best I can and hit ti with a bit of rust reformer spray. Wish me luck...