Got my refinished gas tank mounted a while ago and just recently filled it up, but to find gas leaking. The leak is at the seal for the unit gauge. I pulled the unit and remounted using a gas resistant sealent after cleaning it very well. Actually I did this about four times with no success. I then tried with no sealent and it continued to leak. About 6 years ago I pulled the tank and remounted it with no problem (leaks). The only thing different is that part of the refinishing job was a primer coat. The primer, at least now, is comming off because of the gas and being scraped. Could this prevent a good seal? The primer was intact the first time is tried this time but it got worse every time I tried to mount the gage. I did not do any sanding or scraping as I did not want to make it worse. i did not try a gasket because I was not sure that the lock would fit. Is there a solution to this problem. Please do not tell me I have to remove the gas tank!! Well, I will if necessary.

aapiss:

Your post doesn't mention whether you used the required O-ring when you installed the sender unit. If you didn't, well there is your problem. If you used the old O-ring, it must be in "perfect" condition? If it is not, there is your problem. The O-ring MUST be used and MUST be free of nicks, squashed areas from bad mounting attempts, or other abnormalities. Best bet is to ALWAYS use a NEW O-ring when removing and replacing the sender unit. It is very cheap insurance against leaks. The sender can be removed and replaced without removal of the gas tank.

Not trying to insult your intelligence or Z knowlwdge, but the O-ring is critical, and frankly, your mention of not using a gasket has led me to my questions about the O-ring. There is no need for a "gasket", you DO need the O-ring!

Careful installation of the sender with a new O-ring is quite simple and is almost always leak free (unless the sealing flange of the gas tank is damaged). The primer should have no effect on the mounting or sealing of the sending unit to the gas tank.

Let us know how it comes out!

Carl:classic:

No need to worry about insulting my intelligence. I recognize my lack of knowledge on car repair matters that I am not afraid to ask questions. The two times I have had the sending unit out I have not seen an O ring. My repair manual does not show one in the diagram nor does it talk about one. Is this a special O ring for this tank or will any of the correct diameter and thickness work?

There is a specific O-Ring available through Motorsport Auto, or Nissan (if still available) for the purpose. I believe that any O-Ring of the correct diameter and thickness will work. The diameter should be easy to figure out with the sender removed, you'll see an indentation around the opening for the sender, as for the thickness, I don't know how thick it needs to be, but since o-rings are not too expensive, I'd get several thjicknesses. THE ONE THING TO REMEMBER if using a generic O-ring is that it needs to be made of a material that is designed for use with gasoline. If it is the wrong material, it will dissolve in short order and the leak will be back. Check with local parts dealer or........

My reccomendation is to get one from Motorsport Auto. P/n from MSA is 11-3280 Catalog says multiple applications, so you'll need to tell them what year car you have and maybe the Mfg date to get the right part. They are at 1-800-633-6331 and are open short hours on Saturday for ordering.

Good Luck

Carl

Carl,

You said that you can install the sender without have to remove the tank. I need to check the wiring at the sender, since my guage stopped working. I looked under their yesterday and could not even see the thing. How do you get to it?

Thanks,

Marty

Hey Marty:

First of all, I should say that I'm refering to a 1972 240Z. On my car the sender is at the front wall of the gas tank, on the passenger side of the car. There are two wires that connect to the sender unit and they ("it" the sender) are quite obvious. A circular lock-ring compresses the o-ring which seals the sender to the front wall of the gas tank. Use a flat blade screwdriver against one of the tabs on the lock-ring to rotate the ring. The ring will then come loose and the sender can be removed. The float of the sender is on a long arm, so be careful as you pull it out so you don't bend the arm.

Major Warning!! The fuel tank must be almost completely EMPTY before attempting this

Check a Haynes or FSM for more detail. If you have further questions, let me know!

Later,

Carl

Another precaution, and I will not say that it happened to me. When you hook the wires to the posts on the sending unit, do not force them, the posts may pop out of the sending unit. I don't think they can be put back in and the little wire inside is broken anyway. If this happens and you get a new sending unit, I would be very careful. Might be wise to pare some of the rubber off to expose the clip so you can see what you are doing. Then put a dab of silicone sealer on the connection. The connectors inside the rubber housing may be brittle with age also. I will follow my own advice with my new sending unit. (Oops, did I switch from third person to first person?).

I did finally get a good seal but not with an O ring, it still leaked. I put some of that sealer from the tube on then cut a gasket from some good gasket material. Installed it and it held, but then......I did get past the swearing stage however.

There is a possibility that when the tank is filled up to the sender there will still be a leak which means that gas must be drained again, the sender reinstalled, and refilled to retest. This is hazardous to say the least. Is there another way to test? Would draining the tank and refilling with water work? This assumes that all of the water can be drained. Is this a bad idea?

I am getting very intimate with this gas tank! Is there a forum for DUMB stories here

Well the gas tank ordeal is over at last. Due to cluminess, I had to buy a new sending unit and also got an o ring and retaining ring as well from Motor Sport. Tried two times to get a seal while the tank was mounted with no success so dropped the tank. Even then it took two tries to get a seal. Tested the seal with gas in the tank-my idea of using water was not a good one! I have been fooling around with this tank for so long I still do not believe it is sealed and I still have to check for leaks around the seal. Man, I would really hate to get rear ended - great balls of fire.

Originally posted by aapiss

Man, I would really hate to get rear ended - great balls of fire.

You have just discovered one of the main reasons that the FEDS mandated the 2.5 MPH, then the 5 MPH bumpers beginning in 1973. Not that they help tremendously, but they certainly ARE an improvement!

Enjoy the Ride!

CarlROFL

I wish someone smarter than I would come u p with an automatic shut off of the electric fuel pump , if in an accident you flip over or if in a collision. As an retired fireman I have seen enough that I dont want to be french fried in my own gas. If it could be connected to the oil pressure sender so if no oil pressure then the fuel pump would stop. Just a thought .