Leak at the fuel sending unit

[SteveJ]

I replaced the fuel sending unit on my 74 today. I thought I had a new O-ring, but I couldn't find it. When I removed the old sending unit, the O-ring appeared fine, so I decided to re-use it. I tweaked on the retaining ring a little because I wasn't smart enough to leave well enough alone. It puts plenty of pressure against the fuel sending unit and O-ring. However, when I tried to put in some gas, it leaked at the sending unit. I got the gas level below the sending unit and worked on it some more. I think the first time I put the ring back on it may have slid over to the side some and not remained centered in the opening. I put the ring back in place again, carefully ensuring the ring was centered properly. A friend slowly added gas, but the leak remained.

I went ahead and ordered a new O-ring and retaining ring from MSA. I hope to have it around Thursday or so. I'd like to hedge my bets, though, and ask for input on any other reason for the tank to leak at the sending unit besides not centering the retaining ring or replacing the O-ring.

Thank you in advance for any suggestions.

[zKars]

One important detail is the cleanliness and smoothness of the surfaces where the o-ring seats, and the oring itself. Do all you can to clean everything and inspect the o-ring for damage. No power tools, just fingers and sandpaper or steel wool.

Next is the pressure applied by the ring, and the centering of the ring as you tighten it. Is the ring rusty or corroded?

[SteveJ]

Thanks, Jim. The old ring was a little corroded, but not too bad. Fortunately, I found a new retaining ring in my parts stash a few minutes ago. If I was organized, I might actually catalog all of the stuff I've been accumulating. I did not look at the sealing surface at the tank, though I imagine it's pretty nasty. I cleaned the gunk off of the O-ring with carb cleaner, and it passed my cursory inspection. That doesn't mean it was still up to snuff.

Thanks for the info.

[FastWoman]

Dunno... I know it was very bad form, but I reused my O-ring when I re-did my tank. It looked in good condition, and I made certain all surfaces were clean and smooth. As far as I could tell, no leaks. I suppose someday I should top off the tank and pull the inspection plate to be certain.

Anyway, you might indeed have your O-ring askew.

Edited July 5, 2011 by FastWoman

[AZ-240z]

When you put the O-ring back in, put a little lub on it. This will keep it from distorting and being pushed out of postion when you tighten the retainer ring.

[robftw]

Put a drop of oil around the O-ring too, it'll help the seal.

I've always used DOW33, or DOW55

Playing years of paintball made me an oring lube expert

[SteveJ]

Thanks for all of the advice. I received a new O-ring yesterday, and I took much greater care in the re-installation. I cleaned the sealing surface of the tank with a soft toothbrush and carb cleaner. I then applied vaseline to the sealing surface of the sending unit to hold the O-ring in place and lubricate the O-ring. I spread a thin coat of vaseline on the O-ring, too. I eased the sending unit back into the tank and made sure the notch on the sender fit right around the key on the tank. I put the retaining ring on and rotated it with two pairs of pliers to ensure that the ring rotated around it's center. (I had used a screwdriver to push it before.) With my wife watching the tank, I added plenty of gas. There were no leaks.

Unfortunately I was able to confirm that my gas gauge has given up the ghost. If anybody has a spare one that he/she can part with, send me a PM. I'd love to get my hands on one quickly.

[ConchZ]

Doesn't vaseline eat rubber?

[olzed]

O rings are impervious to most anything.

[SteveJ]

Doesn't vaseline eat rubber?

Vaseline is not compatible with latex rubber. The O-rings are another form of rubber. Latex wouldn't stand up to gasoline, either.

If a product holds up against gasoline, I would guess it would hold up to vaseline. Gasoline is an excellent solvent, after all.

Edited July 9, 2011 by SteveJ

[SteveJ]

I also found this link about petroleum jelly and nitrile (See post #7): http://www.candlepowerforums.com/vb/showthread.php?113228-Nitrile-Buna-N(O-Rings)-vs-Petroleum-Jelly(Vaseline)