Fuel tank leak test using a water manometer

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Testing for leaks


I checked the tanks for leaks using a simple water manometer to accurately monitor pressure changes (note the plastic tubes with the red liquid on the left side of the picture). I mixed a few drops of food coloring into the water to make it more visible. A difference in height of approximately 27 inches between the two columns is equal to 1 psi. I started with about 48" of water pressure, but that caused a noticeable bulging of the lower tank skin between ribs, so I quickly reduced the pressure. Fortunately there was no permanent deformation. Be careful, it doesn't take much pressure to ruin the tank skins. I would not go above 1 psi. You need to monitor the temperature while performing the leak test as the pressure would change significantly with even slight temperature changes. The only leaks that I found were through the filler caps. I disassembled the caps and greased the o-rings with FuelLube to get the caps to seal. (Actually, one cap still leaks slightly, but neither tank leaked with the good cap installed.) The water manometer is a very sensitive leak detector. One of my caps had a leak that was so small that it was hard to detect with soapy water. It would take a minute for one small bubble to appear. Yet even with this small leak, the water column would lose several inches overnight. I was relieved to find that my tanks were completely free of leaks. (By the way, I still have about two thirds of the tank sealant left over after doing both tanks.)

Note: A few people who have viewed this page thought that I had put water in the tanks. However, nothing but air was ever put into the tanks. The only liquid involved is in the u-shaped tube which is used to measure the air pressure in the tank being tested.

Ready to install


After leak testing, the end ribs and back of the tanks were primed. I was glad to finish this part of the project.
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Updated 1/30/02 (note added)