? sealing leak at neck of fuel tank - The 1947 - Present Chevrolet & GMC Truck Message Board Network

webhendrix · 10-06-2003, 05:33 PM

I had replaced my fuel tank earlier this summer and had filled it up for the first time today (as I had not been driving it yet, just working on it) and noticed that it will leak from the weld where the neck goes into the tank (on the back side of the neck).

Is there anything I can seal that with?

To me it is a very small minor leak which can be avoided by not filling the tank up all the way but now I would guess that it would not pass the pressure test when I take it to the VET.

The other problem is my full gauge reads empty and the sending unit is new (and in good position) and the wire is new. When I have the wire off of the tank the needle goes way pass the full mark but if I put the wire back on, it slowly goes back to the empty mark???

Thanks for any tips!

71GMC_3/4T · 10-06-2003, 06:00 PM

Wait till the tank is less than 1/2 full and clean and patch the hole with some epoxy type fuel tank repair/sealer. You should be able to find it at your local auto parts store. Usually a "ribbon" of epoxy. Tear off what you need, knead it, and install. Be sure to clean the area first with scotch brite or something like that.
I wouldn't worry too much about the seal test. Most of these systems were vented caps anyway.

For the guage problem, it sounds like you have a bad sending unit or a sunk float. I've heard wine bottle corks work great too. Chances are someone on here has one they can sell to you. I don't think you can buy just the float new.

BLACK AND BLUE 67-72 · 10-06-2003, 06:01 PM

For the leak, try some J-B Weld or you can try to solder it. As far as the guage goes is your tank grounded good? If not the guage will not read right, so you might try a piece of wire attached to a good ground and touch the other end to the tank near the sending unit, If that doesn't work then your sending unit may not be the right OHMS for your guage to work properly or it could just be faulty. Did it work with the old sending unit? If so try switching back to the old one and see if the guage starts working or not. I just went through this, this weekend with the leaking neck and the faulty sending unit.

71GMC_3/4T · 10-06-2003, 06:28 PM

If the guage goes to empty, the ground must be fine. Lack of ground would cause an over full reading, just like when the wire is open.

I missed the part where it was a new sending unit. Is it possible you bent something internal when you installed it? It's pretty simple. Just a rheostat between ground and the stud the wire hooks to.

Look into the tank and see if you can see the float toward the bottom of the full tank. Use a flashlight - not a match...

jorgensensc · 10-06-2003, 10:50 PM

My gauge does the same thing. I can't figure it out either. Mine reads past full all of the time. If I remove te wire, nothing happens, but if I touch it to the screws or a tab on the sending unit it will go to empty. Please help us

I drive my truck daily and have to guesstimate my fuel level by the sloshing in the tank.

71GMC_3/4T · 10-07-2003, 09:57 AM

Jorgensensc - you have an open sending unit. The guage works like it should, open ckt = F, short to gnd = E.
The only cure is to replace it unless you can spot something obvious when you remove it.

jorgensensc · 10-07-2003, 02:44 PM

Thanks for the help. I'm going to be replacing it with a blazer tank soon, so it really won't matter I guess. I was hoping it was just something simple.

Denny · 10-07-2003, 10:53 PM

I had the same problem with a new tank I bought from LMC a couple years ago, I soldered mine with a large sodering iron.

Longhorn Man · 10-07-2003, 10:56 PM

jorgensensc, look at the brown wire on the sending unit. Folow it untill you see where it is broke. (99% chance that's the problem)
I'm willing to bet that it is under the chrome trim at teh bottom of the drivers door. (The sill plate)

As for the fuel leak, If you want to have it repaired properly, then you'll need to remove the tank, steam clean it out for a good 5 to 9 hrs, (steam clean untill there is NO fuel smell) then solder the neck back on.
A rad shop can do this for you for not much money. I had a thread going about this but I was getting too many ppl talking bout blazer tanks and little to no interest on what I was posting so i let the thread die.
Here's the thread. I still have not dumped the POR stuff in there...maybe this week. The weather is supposed to be favorable.

jorgensensc · 10-07-2003, 11:07 PM

Longhorn Man,
Thanks for the reply! I Used my multimeter(the absolute best investment ever!) and ohmed out the wire from the fuse block and from the gauge cluster to the sending unit. It ohmed out fine. I think there is probably something wrong with the fuel sending unit. I can hear something rolling around in my tank when I turn corners. Thanks for taking the time to respond!
Shawn

10-06-2003, 05:33 PM	#1
webhendrix Registered User Join Date: Aug 2003 Location: kentucky Posts: 6	? sealing leak at neck of fuel tank I had replaced my fuel tank earlier this summer and had filled it up for the first time today (as I had not been driving it yet, just working on it) and noticed that it will leak from the weld where the neck goes into the tank (on the back side of the neck). Is there anything I can seal that with? To me it is a very small minor leak which can be avoided by not filling the tank up all the way but now I would guess that it would not pass the pressure test when I take it to the VET. The other problem is my full gauge reads empty and the sending unit is new (and in good position) and the wire is new. When I have the wire off of the tank the needle goes way pass the full mark but if I put the wire back on, it slowly goes back to the empty mark??? Thanks for any tips!

10-06-2003, 06:00 PM	#2
71GMC_3/4T Weapons Of Construction Join Date: Apr 2000 Location: Colorado, USA Posts: 1,095	Wait till the tank is less than 1/2 full and clean and patch the hole with some epoxy type fuel tank repair/sealer. You should be able to find it at your local auto parts store. Usually a "ribbon" of epoxy. Tear off what you need, knead it, and install. Be sure to clean the area first with scotch brite or something like that. I wouldn't worry too much about the seal test. Most of these systems were vented caps anyway. For the guage problem, it sounds like you have a bad sending unit or a sunk float. I've heard wine bottle corks work great too. Chances are someone on here has one they can sell to you. I don't think you can buy just the float new. __________________ 1971 GMC 2500, 402/TH400 4.10 Daily Driver Lafayette, CO

10-06-2003, 06:01 PM	#3
BLACK AND BLUE 67-72 Firefighter Join Date: Feb 2001 Location: Yellville, Ar, USA Posts: 1,943	For the leak, try some J-B Weld or you can try to solder it. As far as the guage goes is your tank grounded good? If not the guage will not read right, so you might try a piece of wire attached to a good ground and touch the other end to the tank near the sending unit, If that doesn't work then your sending unit may not be the right OHMS for your guage to work properly or it could just be faulty. Did it work with the old sending unit? If so try switching back to the old one and see if the guage starts working or not. I just went through this, this weekend with the leaking neck and the faulty sending unit. __________________ '72 Chevy SWB 350 Auto '67 GMC LWB 350 4 speed '70 Chevy 4x4 Stepside 350 Auto Yellville, Ar. USA

10-06-2003, 06:28 PM	#4
71GMC_3/4T Weapons Of Construction Join Date: Apr 2000 Location: Colorado, USA Posts: 1,095	If the guage goes to empty, the ground must be fine. Lack of ground would cause an over full reading, just like when the wire is open. I missed the part where it was a new sending unit. Is it possible you bent something internal when you installed it? It's pretty simple. Just a rheostat between ground and the stud the wire hooks to. Look into the tank and see if you can see the float toward the bottom of the full tank. Use a flashlight - not a match... __________________ 1971 GMC 2500, 402/TH400 4.10 Daily Driver Lafayette, CO

10-06-2003, 10:50 PM	#5
jorgensensc Registered User Join Date: Jul 2003 Location: Cypress, Tx Posts: 4,005	My gauge does the same thing. I can't figure it out either. Mine reads past full all of the time. If I remove te wire, nothing happens, but if I touch it to the screws or a tab on the sending unit it will go to empty. Please help us I drive my truck daily and have to guesstimate my fuel level by the sloshing in the tank. __________________ 1972 C20 Suburban- Big Blue Betty '56 Chevy Bel Air Sedan- Frame up Restoration -What would you attempt to achieve if you knew you could not fail?- -I Refuse To Tiptoe Through Life, Only To Arrive Safely At Death's Door- R.I.P. EAST SIDE LOW LIFE

10-07-2003, 09:57 AM	#6
71GMC_3/4T Weapons Of Construction Join Date: Apr 2000 Location: Colorado, USA Posts: 1,095	Jorgensensc - you have an open sending unit. The guage works like it should, open ckt = F, short to gnd = E. The only cure is to replace it unless you can spot something obvious when you remove it. __________________ 1971 GMC 2500, 402/TH400 4.10 Daily Driver Lafayette, CO

10-07-2003, 02:44 PM	#7
jorgensensc Registered User Join Date: Jul 2003 Location: Cypress, Tx Posts: 4,005	Thanks for the help. I'm going to be replacing it with a blazer tank soon, so it really won't matter I guess. I was hoping it was just something simple. __________________ 1972 C20 Suburban- Big Blue Betty '56 Chevy Bel Air Sedan- Frame up Restoration -What would you attempt to achieve if you knew you could not fail?- -I Refuse To Tiptoe Through Life, Only To Arrive Safely At Death's Door- R.I.P. EAST SIDE LOW LIFE

10-07-2003, 10:53 PM	#8
Denny Registered User Join Date: Jul 2002 Location: Cedar Hill, MO Posts: 426	I had the same problem with a new tank I bought from LMC a couple years ago, I soldered mine with a large sodering iron. __________________ 1969 Chevy C10. Dakota Digital Gauges, 383 Votex Engine, MSD 8361 Distributor, MSD 6A Unit, Demon Carb, Phoenix Transmission 4L80E trans, 3:73 Posi Rear End Early Classics 6 Lug Disc Brakes and Spindles All Stainless Lines

10-07-2003, 10:56 PM	#9
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,693	jorgensensc, look at the brown wire on the sending unit. Folow it untill you see where it is broke. (99% chance that's the problem) I'm willing to bet that it is under the chrome trim at teh bottom of the drivers door. (The sill plate) As for the fuel leak, If you want to have it repaired properly, then you'll need to remove the tank, steam clean it out for a good 5 to 9 hrs, (steam clean untill there is NO fuel smell) then solder the neck back on. A rad shop can do this for you for not much money. I had a thread going about this but I was getting too many ppl talking bout blazer tanks and little to no interest on what I was posting so i let the thread die. Here's the thread. I still have not dumped the POR stuff in there...maybe this week. The weather is supposed to be favorable.

10-07-2003, 11:07 PM	#10
jorgensensc Registered User Join Date: Jul 2003 Location: Cypress, Tx Posts: 4,005	Longhorn Man, Thanks for the reply! I Used my multimeter(the absolute best investment ever!) and ohmed out the wire from the fuse block and from the gauge cluster to the sending unit. It ohmed out fine. I think there is probably something wrong with the fuel sending unit. I can hear something rolling around in my tank when I turn corners. Thanks for taking the time to respond! Shawn __________________ 1972 C20 Suburban- Big Blue Betty '56 Chevy Bel Air Sedan- Frame up Restoration -What would you attempt to achieve if you knew you could not fail?- -I Refuse To Tiptoe Through Life, Only To Arrive Safely At Death's Door- R.I.P. EAST SIDE LOW LIFE



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