Gas Cap leaks

Z

Zmanx98

New member
I am building a 1931 slantwindow and am getting close to painting but I need to solve a gas cap problem first. I have read other post and trued the Eaton style cap from Snyder's. I have a cheap single rivet cap and even changed the gaskets to but new leather gaskets on them. My problem is not the gas sloshing out on the tank but the fumes coming out of the tank and messing up the primer and are quite noticeable where the vents are. This happens mostly while the car is setting still in the shop. I know the purpose is to vent the tank but the fumes are doing a lot of damage.
Does anyone have a suggestion I have not tried?
 
I have experienced the same problem when the car sets for a period of time. Because I use Marvel Mystery Oil, it leaves a small trail of an oil like substance from the gas cap to towards the engine compartment. I have good gaskets but it appears to be coming through the vents. I am using regular gas not ethanol.


When the car ('29) is going to be setting for an extended time, I tie a strip of rag around the gas filler threaded hole just under the gas cap.



I just checked it, after setting for five months the top of the tank was clean.


I don't know the real answer to fix this problem but my "farmer fix" keeps me from having to polish out the little trail of oil.
 
My question is; why have gas in it at all? Drain the tank and plug the opening. If you need to move the car, hang a small tank off the hood rod.
 
redmodelt said:
My question is; why have gas in it at all? Drain the tank and plug the opening. If you need to move the car, hang a small tank off the hood rod.
Click to expand...


Draining the tank is a good point for a lengthy storage of the car. I failed to also note that this also happens over a shorter period of time. In the space of one or two weeks I have noticed this starting to happen. I assume that if I stopped using MMO, there would be no indication of anything happening as the gas would evaporate through the vents and leave no residue on the top of the tank.



As far as draining the tank during long periods of storage - the garage where I store the car for the winter months is not heated. I experience a lot of condensation as the weather starts to warm up. In fact, if I don't spray the motor with WD40 when I put the car in storage in the fall the motor will be dripping moisture in the spring.



I assume an empty tank would be condensing moisture on the inside as well, thus a full tank of gas with MMO and rag around the cap.
 
I started with Cromax DTM 2590S epoxy primer and am using Cromax 7707S primer filler over it. Used to be Dupont products before they sold.
As for draining the tank, doesn't that just hide a problem that will be real ugly once I get paint on the car. I have seen more than 1 31 model swap meets with similar problems. But, no one told me they found a resolution to it.

The rag around the cap my be my best solution, for now.
 
You don't mention if the primers you are using are over any older paint or bare metal. In either case, have you significantly scuffed the area around the rim of the gas cap opening on the tank enough for the paint to grip well. This area can be sanded with a grit a bit heavier than you used on the tank itself without worry of how it will look after paint. Much like door edges, this area needs to be really well prepared for paint to grip properly. Paint failure as you are referring to starts more easily where any edge is concerned.

Next question, if you are thinning the primers, are you using reducers from same manufacturer or generic paint store brands? Are the reducers compatible with air temperatures at time of application? How warm was it when you applied the primers? I have used epoxy primer for years to paint Zenith carburetors. I started having issues with gasoline intolerance when I used lesser quality reducers or sprayed at temperatures less than the desired 65 degrees it takes for most epoxy primers to bind optimally.

Hope this helps. Good luck

Bob Bader
 
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