1966 Fuel Sending Unit O Ring Leak

PeterMAX

PeterMAX

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Joined
Jul 24, 2017
Thunderbird Year
1991
On a 1966 Thunderbird we have a NEW Spectra Premium Fuel Tank, a NEW sending unit and all new fuel lines. When the tank is full and parked on an incline fuel leaks from the sending unit. We have replaced the "square" O ring 2 times,and are reasonably certain it is properly seated. We are at wits end on this problem and are prepared to pull the tank, clean the area, and seal it with JB Weld. Before doing so, we'd be interested in hearing from others who have dealt with this issue and how you dealt with it, Any thoughts much appreciated. Thanks.
 
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PeterMAX said:
On a 1966 Thunderbird we have a NEW Spectra Premium Fuel Tank, a NEW sending unit and all new fuel lines. When the tank is full and parked on an incline fuel leaks from the sending unit. We have replaced the "square" O ring 2 times,and are reasonably certain it is properly seated. We are at wits end on this problem and are prepared to pull the tank, clean the area, and seal it with JB Weld. Before doing so, we'd be interested in hearing from others who have dealt with this issue and how you dealt with it, Any thoughts much appreciated. Thanks.
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since it is a rubber seal, I did not use sealer on mine. I just cleaned up the mating surfaces and put in new rubber seal and then used a piece of wood and a small hammer and tapped the clip around in place. I also replace the gas cap. seems like we were getting a lot of fumes from that area. I know my tank is NOT vented out the top account every time I open the gas cap, I get a woosh of air coming out. so give the seal a tap and Mabe fill the tank up 3/4 and then stuff a rag and an air check in the tank and add a little air and see if it's coming out the seal and if it is, tap the seal clip tighter while you're looking at it with the air in the tank.
 
You should have a system that uses a VENTED gas cap. If you replaced the gas cap recently you were probably given a NON-vented cap. Try loosening the gas cap to stop the seeping. If leaving the cap loose stops seeping, then change the cap.
 
New idea. Fill the tank and park the car where you know it will leak. Get some good rags and a high powered light. Dry it off as it's leaking, look hard. It may not be the seal but a poorly sealed pipe coming out. If you cannot positively see the fuel flow dust it with flour to find the trail. Highly possible the sending unit itself is bad.
 
The repro O rings are too small, some owners have soaked the O rings in motor oil overnight and reinstalled them and had them seal sufficiently. This trick depends on the composition of the rubber though.
 
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Frankie the Fink said:
The repro O rings are too small, some owners have soaked the O rings in motor oil overnight and reinstalled them and had them seal sufficiently. This trick depends on the composition of the rubber though.
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I have the tank out and indeed you are 100% correct, the seal is too small. I will try the oil soak method you recommend.
 
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