1961 mystery fuel leak

[MidModCad]

Having a head scratcher of an issue with My '61 coupe. Gave it a full tank of gas, then parked it in my garage where it began reeking of fuel which didn't dissipate for a week.  The smell is coming from somewhere in the rear - very strong around the filler neck. The weird part is everything is dry, there are no tell tale drips anywhere and the gas cap is on tight.  During a test drive today the smell of fuel was strong inside the car while driving uphill (fairly steep).  Checked the fuel lines going into the tank and, while there is some very minor weepage, it doesn't seem anywhere near enough to produce fumes at this intensity. The cap gasket is just so-so, but doesn't smell much, and there is no fuel smell under the hood at all. Prior to this I've have zero issues with the fuel system. Could there be a leak on top of the tank which I can't see?  Vapor return pipe for AC?  One addl. point - there was no fuel smell on the test drive until the engine warmed up.

[Clewisiii]

My original fuel tank was only rusted through on the top. I also had a split rubber neck at the fuel fill neck and split rubber at the tank vent.

[35-709]

Yeah, leaking fuel sender gasket would be my first suspicion, then bad (old) rubber hoses back there seeping gas.  The smell with a full tank though, and a dry floor, certainly points me to the sender gasket though (or a rusted through tank top as Clewisiii experienced).  Should replace those hoses back there anyway if it hasn't been done in a long time.  The smell after warm up - I dunno.  Requires eyes on.

[MidModCad]

Sounds possible.  But wouldn't there be a puddle on the ground?  Or at least drippage?

[Clewisiii]

Sounds possible.  But wouldn't there be a puddle on the ground?  Or at least drippage?

open rust hole on top?  I wouldn't think it would leave a puddle while parked. But it would leak and slosh around while driving. Parked would just have an open gas can smell.

[MidModCad]

Maybe, though the tank isn't rusty anywhere that's visible.  Since it doesn't smell when it's first driven, I'm thinking the bad sender gasket theory might be the culprit. Once the gas inside sloshes around, the gasket gets soaked, it seeps out then sits inside the indentation for the sender.  Would explain why there's never enough to run down the side of the tank and hit the floor - also, why the smell dissipates after a few days.  Sound reasonable?

[dadscad]

I had a similar problem with my 63 many years ago. Had a strong gas smell after a fill up when the car was sitting in the garage. Didn't have any visible leakage but but definitely had a strong smell. I pulled the tank and found the sending unit gasket to be the culprit. I made a new gasket and reinstalled everything, that solved the problem.

[tcom2027]

Yeah, leaking fuel sender gasket would be my first suspicion, then bad (old) rubber hoses back there seeping gas.  The smell with a full tank though, and a dry floor, certainly points me to the sender gasket though (or a rusted through tank top as Clewisiii experienced).  Should replace those hoses back there anyway if it hasn't been done in a long time.  The smell after warm up - I dunno.  Requires eyes on.

I agree. WIthout knowing if he is in iron worms country there will likely be rust in the stamped depression holding the sender. WOuldn't be surprised if once the rust was removed there will be pin holes in the tank.

THen it's time for the J-B Weld or Davcon epoxy.

[Clewisiii]

Soon I will be ordering a new fuel tank. For an extra $200 I am just going to get a stainless steel one.

A regular steel tank would probably last me just fine. But I see no downside to having the comfort of a stainless tank.

[dn010]

It will depend on the kind of stainless it is made out of - certain grades will still rust and it will be difficult to know what is going on inside the tank.

For those who can't get a tank because they aren't making them, or if one doesn't want to replace theirs, KBS Coatings make a great Fuel Tank Sealer system. I've used it on/in many different tanks, including my 57 back in 2008 that is still holding up perfectly to this day. Not only does it seal up pinholes, it also covers all the rust and any micro debris that you may not have been able to get out of the tank.

https://www.kbs-coatings.com/kbs-tank-sealer-system

[jwwseville60]

Please be advised that tank coatings only last 15 years at most.
I vote stainless.

[Clewisiii]

Can I ask you to take a picture of where your hard fuel lines stop over the rear end before it transitions for rubber.

I have new lines to bolt to my body. But i cannot figure out front to back or how they should postion.

[ZGJim]

The originality of my '61 deVille coupe is questionable.  The hard line ends in front of the axle and the rubber line connects to the tank from there.
The service manual doesn't really show where the hard line ends.  It also shows a "vapor return" line that is not present on my car.
Hope this helps.

[The Tassie Devil(le)]

Please be advised that tank coatings only last 15 years at most.
I vote stainless.

I can attest to the problems with internal coatings.

I was doing a restoration on a car, and the tank needed to be coated.  Everything was going well, until one time, months later, the fuel line became blocked.  Blowing it out with compressed air cleared the obstruction, till it happened again.

What was causing the blockage was small rolls on paint that was coming off the insides of the tank, and getting into the pickup tube.

The fix was a replacement tank, which eventually became available.  None were being reproduced at the time of the initial restoration.

Bruce.