MTFCA Forum

I have a ‘27 Coupe and I have detected a very slight fuel leak where the overflow line exits the tank. The leak is not coming from inside the overflow line but is leaking around the outer diameter of the pipe. I’d like to get thoughts on how to fix this.

It could be leaking where the outlet fitting is soldered to the bottom of the tank or the overflow tube inside the tank is rusted and perforated. It's not uncommon for a 90+ year old tank. If you can't determine exactly where it's leaking while in the car, your going to have to remove the tank.

Your overflow tube has been cut way short. It should extend to the frame. That slotted screw holds it in. Its been cut to an inch or so.
Are you absolutely sure its not fuel from sloshing fuel & actual overflow as designed?
If thats an actual leak, its from the inner tube lower solder joint or the tube has a pin hole inside the tank.
The "quick fix" would be to slosh the tank with sealer. ugh. Best to solder repair/replace the inner tube.

Thanks..I am obviously new to the Model T world and with one eye closed and my iphone and flashlight I just realized that it is the nub of the overflow downtube. I am not certain at this point where the leak is. Looks like first task is to try and remove that long set screw which has one ear of the screwdriver slot snapped off. Let the fun begin!

Unfortunately, the Cowl tank is the only one there have not been replacement tanks made over the years, so if you need to replace it, you will need to find a good one for sale that someone has removed from a parted car. That tube goes all the way through the tank to the filler, right next to the place where you fill the tank, so if you should happen to over fill the tank, or spill some while fueling up, it will run down that pipe instead of getting inside the car. Having posted all the above, you might not actually have a leak, but have sloshed some gas from the top when filling, or even on a hot day if you fill up when the car is cold in the morning, and then park the car, the gas could expand and overflow.
I would recommend that you buy the replacement pipe from that screw to the frame of the car and install it. Perhaps put a little fuel proof sealer right where it is attached at the screw. Then put something under it when you are parked and see if you get any drips. If you need work on the tank, you will need a professional who can disassemble it and repair inside. If you boil out the tank and put sealer inside, it could solve the problem however you need a sealer which is not soluble in alcohol which all the newer fuels contain.
Norm

I had a similar problem with my 26 touring. Some may not approve of my fix, but it has worked for me.

My tank was reasonably clean and serviceable except it leaked from pin holes in the overflow tube inside the tank. I removed the extended tube on the firewall and thoroughly cleaned and dried the opening under the tank then stuffed it as tight as I could with a JB weld product that has the consistency of play doh. That was five years ago, it hasn't leaked but I did have to cover the opening at the top to stop gas fumes from getting in the car. The overflow tube is not critical. With a little care, you can fill your tank without spilling. Motorcyclists do it every day.

You will not be able to see as there are baffles.
These three you can do without removing the tank:
At your own risk you may want to try a pressure test with the tube extension removed, while plugging up one end for either a gauge or listen for bubbles entering the tank (fill cap removed, fuel in tank).
You may want to try running a swab down from the top down with wire into the overflow tube. Pull it back up and see what you get each time.
At your own risk you may pressure the tank from the top, with the sediment cock closed. Use a mirror and light from the bottom side.

We spent the last two months cleaning the tank with vinegar, then ran the POR15 treatment kit $$, per instructions. We installed it and the dash. Tomorrow, we put gas in it for the first time to see if it leaks.

Thanks to all that have replied! I very much value your experience and expertise. I have to travel tomorrow for two weeks but when I return and sort this out, I will follow up with what I have done and the results!

You can do it. It's not rocket science.

There is a local radiator shop that has boiled and relined 6 tanks for me. My '26 pickup had a constant drip coming out of the overflow tube. The shop owner told me that the tube is not a PIPE, but instead is thin sheet metal rolled (layered) to form a tube. He said that the layering was the cause of the leaking. When he sealed the tank- the leak stopped. And, that was 12 to 15 years ago. I didn't actually see the tube so can anyone verify the shop owner's statement? If so, the layering could possibly be the cause of Ken's problem.

If you can possibly fix the leak without removing the tank - I suggest that you do so. Removing the cowl-mounted tank is not a fun project. It's not rocket science, but there is a fair amount of disassembly involved.