Fumes

[jf100]

I have a 69 F 100 Custom Cab. The gas tank is behind the seat. When I fill it up and it is a warm day I can smell fumes. I have not noticed any leaks. Can someone tell me what to use and how to use it to seal up the tank from the inside. Any ideas on how long it will take or would it be better to take it some place? I have to leave the windows cracked when it sits over night or in the day while I am at work then it is open all windows and vents and run the fan until it gets to about a 1/2 tank. Thank you for any help.

[Manny]

Best bet would be to reseal you filler neck on the tank. Also reseal the sending unit in the tank and redo your lines. Easy job with the parts available from multiple vendors. LMC, Denniscarpenter, NPD all of them will have it. With basic tools and an afternoon should be no issue for you to knock out. That would be the best option if the tank is not leaking. Getting the fumes out will definitely help your driving experience.

[jjdeal79]

What about a cracked inlet hose? I know OP said vapors away around 1/2 a tank.....
Oh, just saw post by Manny.....

[dpson]

I had a similar issue on my 69 and found the gasoline smell was coming from the fuel sender. This was a "replacement" unit installed by the previous owner just a few years ago. Surprisingly it wasn't the seal between the sender and the tank but instead was the rubber seal in the sender unit where the electrical post passes through the mounting plate. Upon disassembly it appears the rubber "gasket" used here is not completely gasoline (or alcohol) resistant and had deteriorated and cracked to the point where it was allowing gasoline to leak by. I suspect its another case of a cheaper material used by an overseas manufacturer that looks and works well initially but breaks down over a relatively short period of time.

[Busboy]

I have the same problem sometimes on my 69. Both tanks and everything related is new. My theory is that the tanks pressurize on a warm day to push vapors out of any weak spot. The caps are vented but only to allow air into the tanks as fuel is consumed. They are not vented the other way. When I pull the cap off there is major ate pressure escaping.

[colnago]

My leak was the gasket around the sending unit. I asked at the auto store what to use that would stand up to gas. They sold me some version of Permatex that didn't harden 100%. Mine actually leaked a small bit when I filled the tank, and would leave a little gas on top of the tank. That's why mine would smell. After a few days of driving, the level was down enough to not splash out.

Joseph

On edit, I found what I used. Permatex #2 Form-a-Gasket non-hardening pliable sealant. Item #80016 (2B). Not sure if that means anything, but it's printed on the tube.