The Boating Forum - Marine Tex or JB Weld?

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View Full Version : Marine Tex or JB Weld?


Fechmup
04-19-2011, 08:44 AM
I have an issue with the sending unit on my 40 gallon gas tank. Last summer, I rounded out a hole putting a new sending unit in incorrectly. I tried to upsize by retapping the hole and still have a leak. The tank is 5 years old and I need to cut the floor up to replace it - not happening if I can help it.

I fabricated a mounting plate up at work to which I can mount the sending unit that I'd like to epoxy to the top of the tank. From my internet searches, I can't seem to find a general consensus on which product would work better in my case: Marine Tex or JB Weld. I have JB Weld, JB Weld Marine, and Marine Tex sitting on the work bench. I'm open to suggestions if I should buy something else.

Thanks is advance for your responses!


the good life
04-19-2011, 10:14 AM
I'm no help, but I've heard of a lot of gearheads who actually use JB weld to seal up gas tank leaks! ;? But then again, as soon as I smell gas, I get paranoid. The last time I had a gas filler neck crack, I had a shop remove the tank and re weld the filler neck. Gas fumes are your big enemy.

fishingfun
04-19-2011, 10:20 AM
Are you talking about stripping a screw hole. I did the same thing and use self tapping sheet metal screws (found some SS) and they worked great. I watched the gasket and as I saw it smash down I quit trying to tighten the screw anymore. The screws actually has a nut shaped head so I could use a ratchet.


Fechmup
04-19-2011, 10:39 AM
Are you talking about stripping a screw hole. I did the same thing and use self tapping sheet metal screws (found some SS) and they worked great. I watched the gasket and as I saw it smash down I quit trying to tighten the screw anymore. The screws actually has a nut shaped head so I could use a ratchet.

Yes Sir - I tried that as well. I neglected to mention that the previous owner gauged the top of the tank. It's as if they were using a screwdriver to scrape something off it. ;? :( The rubber gasket is not sealing and Permatex 2B isn't working either. Epoxying this plate to the top of the tank is my last ditch effort before having to replace it.

I have a $2000 quote to cut up the floor, replace tank, and replace floor, I have $7000 into the boat in the last 8 months, I'd like give epoxy a try.

Capttater
04-19-2011, 11:22 AM
JB Weld.. known to work on aluminum fuel tanks. EZPZ

drem312
04-19-2011, 12:52 PM
Can you put a larger self tapping screw in there filled . Jb weld works great I kudt

DoubleO7
04-19-2011, 01:02 PM
Is it an aluminum or poly or fiberglass tank?
Or steel or stainless steel
or Monel?

It appears that the new mounting plate is to be a drop it in and expoxy it to the tank job.

After all that work, maybe things would be easier if the mounting plate would have been made with a bolt pattern in it and a matching ring with threaded holes for the inside of the tank??
With gaskets on either side of tank wall all sandwiched between the ring and the mounting plate.

Capttater
04-19-2011, 01:16 PM
I hope not. You need an electrical connection between that sender and the tank. Especially since you'll be sending 12v to it. It need screws too.

Fechmup
04-19-2011, 01:35 PM
Is it an aluminum or poly or fiberglass tank?
Or steel or stainless steel
or Monel?

Sorry, the tank is 1/8 aluminum


It appears that the new mounting plate is to be a drop it in and expoxy it to the tank job.

Yup. The new plate, which is 3.5" in diameter, was drilled and tapped for the original #10-32 x 5/8" stainless screws that come with sending unit kits. My plan was to epoxy this plate to the sending unit opening on the tank using JB Weld or Marine Tex - hence my question.

As I said earlier, I did try tapping it to a larger size and I did try larger sheet metal screws. Because of the gouges on the surface of the tank, the rubber gasket that is supplied with the sender will not seal properly, and permatex 2B failed on 3 different tries. This little project of mine is a last ditch effort to make good on a tank that is otherwise good and safely save myself 2000 dollars.

Thanks to you all for your suggestions so far - let the beatings begin... :(


P.S. Capttater - would you pls elaborate on your comment regarding 12v tank connections? I have a + and - on the top of the sending unit itself, but I believe the rubber gasket would insulate it from the tank.

thanks!

Fechmup
04-19-2011, 01:44 PM
Ding!!! Tater, I think I understand your comment - the 5 screws that bring the sender/tank together serve some electrical purpose other than merely being fasteners; is that true? If so, then I've got a new problem. Yay...

So, you're saying the gas gauge won't work if the sending unit isn't physically connected to the tank via the 5 screws? If so - F@$%!!!
Thanks

DoubleO7
04-19-2011, 02:11 PM
The tank and sending unit "base" need to be grounded.
You should have a pink wire coming from the insulated sender terminal going to you gas gage.

http://i61.photobucket.com/albums/h51/40oldtimer19/Electrics/Gauge-SenderWiring.jpg

Fechmup
04-19-2011, 02:21 PM
Check - I have that, grounded off the negative on the bus bar. The sender and gauge are working properly.

Thank you.

Capttater
04-19-2011, 02:31 PM
SLow down.. The TANK needs to be grounded and it needs to be grounded near that sending unit. Worst case run a wire directly from the ground on the sending unit directly to the tank ground.
You can build up a charge on the tank from filling it with fuel, from sloshing etc. The gas, while not a good conductor can make just a good enough connection, especially with ethanol to make that connection.
That sender needs to be connected to the tank.

C Skip R
04-19-2011, 02:35 PM
JB Weld for steel or anytype of metal and Marine Tek for fiberglass although I am sure they would both work.

docters oarders
04-19-2011, 03:09 PM
there is no 12v + going to the tank level sensor. The sensor works on resistance not power.

Mr. Demeanor
04-19-2011, 03:23 PM
It sounds to me like all you may have needed was a better sealant than just he stock gasket. ThreeBond 1194 is perfect for this. It is designed to withstand gasoline and takes up larger clearances.

DocStressor
04-19-2011, 03:28 PM
There is 12 V at the sender circuit. The gauge determines resistance by measuring the reduction of voltage across the conductor, which is a function of resistance.

Ohm's Law: V = IR

fishingfun
04-19-2011, 03:31 PM
Can you give us a picture of the tank without the sending unit so we can see what your working with.

Capttater
04-19-2011, 03:33 PM
there is no 12v + going to the tank level sensor. The sensor works on resistance not power.
;? It can't measure resistance without sending current.
But regardless, parts of a fuel tank need to be closely electrically connected.

Lyle29464
04-19-2011, 06:53 PM
How about pop rivet ? or make a new gasket and leave one hole closed?

sjef
04-19-2011, 06:59 PM
There is 12 V at the sender circuit. The gauge determines resistance by measuring the reduction of voltage across the conductor, which is a function of resistance.

Ohm's Law: V = IR
Not 12v at the tank sending unit. There are sending units for fuel, oil pressure, temp and many other things that do not have 12 volts present. You can measure the reduction of voltage with much less than 1 volt.
Also the tank usually has a tab on it for bonding purposes. The ground on the sender could run directly to the guage, it is not grounding the tank.

35contender
04-19-2011, 07:19 PM
How about pop rivet ? or make a new gasket and leave one hole closed?

You beat me to it i would make a new gasket ( they sell all different thickness ) :thumbsup:

docters oarders
04-19-2011, 07:22 PM
Not 12v at the tank sending unit. There are sending units for fuel, oil pressure, temp and many other things that do not have 12 volts present. You can measure the reduction of voltage with much less than 1 volt.
Also the tank usually has a tab on it for bonding purposes. The ground on the sender could run directly to the guage, it is not grounding the tank.

x2 . there should not be 12v at the sending unit. The sending unit works off of the ground with just resistance on the ground wire. there is no power going to the tank. if there was BOOM

Lyle29464
04-19-2011, 07:50 PM
The gas gauge sends a 12 volt signal to the tank. If you unhook the sending unit you will read 12 volts on the pink wire from the dash. When you hook the wire to the variable resister it tells the gauge how many ohms to ground and that is where the reading comes from. The current flow is near zero so the 12 volts is never a problem.

Capttater
04-19-2011, 09:06 PM
The gas gauge sends a 12 volt signal to the tank. If you unhook the sending unit you will read 12 volts on the pink wire from the dash. When you hook the wire to the variable resister it tells the gauge how many ohms to ground and that is where the reading comes from. The current flow is near zero so the 12 volts is never a problem.
They don't get it. Heck you could even point out that every Ohm meter needs a power source (battery) where as an ammeter and voltmeter don't unless it's digital. An analog volt or ammeter don't require a power source but an ohmmeter (fuel gauge) does.
:banghead:
Even if it's not 12V at the tank it's still a voltage potential and the sending unit needs to be connected to the tank.

Absolute
04-20-2011, 07:48 PM
FWIW:

We often have to fabricate a plate for these reasons. What we have done before is make a plate bigger than the original FSU then mount the FSU to the new plate. The new plate should have mounting screws away from the original holes.

We NEVER use sealants but always make a gasket from stock we buy from Goodyear Rubber.

Capttater
04-20-2011, 08:25 PM
I use fuel safe gasket sealant for the actual gasket but have filled pitting under the sender with epoxy.



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