ALMOST BLEW UP MY GAS TANK...READ THIS!

Getting back to Scoflaws question. Where did the power come from?

What I have witnessed before, that had similar results, was a hot wire chaffed through on a steel auto fuel tank.
It happened to be large gage wire for a high amperage draw component with a 45 amp fuse which finally blew before the car did.
 
techmitch said:
Getting back to Scoflaws question. Where did the power come from?

What I have witnessed before, that had similar results, was a hot wire chaffed through on a steel auto fuel tank.
It happened to be large gage wire for a high amperage draw component with a 45 amp fuse which finally blew before the car did.
Click to expand...

The answer to your question may be on the other side of that bulkhead in the photo I posted. Looks like some interesting connections. I'm not sure even that would cause the tank to flash unless the wiring is seriously problematic.
 
scoflaw said:
OK, just tell me in a short sentence where the voltage originated from. Ask your buddy for help with that sentence.
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Please realize I am not here to convince people. I asked if anyone had this experience. I can't answer other than thru the ground system. It would take days to trace every circuit for the origination.
But I will ask. Believe me. I want to know.
Will do.
 
PlayDate said:
Fred,

I have stayed out of this thread because frankly because we have never seen anything like this. So....just for clarity is this where you ran the grounding strap from the sender to? If so.....there is no electrical difference between screwing the sender in place and attaching a ground wire to this location.....none. There is no resistance, power reverse or any other electrical fantasy other than a grounded connection.

Now if somehow you hooked up a 12volt power wire to the sender....that could get interesting but grounding the sensor mounting screw to the ground terminal would have no effect.

One of the things about CSR is that the folks here know boats inside out. If something shows up we have NEVER seen before.....that means that it is highly unusual.

I realize you are trying to explain it and cite other experts and actions that you have taken but something else caused the tank to flash....if that is what it did and you are lucky to be alive.

index.php
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With the Sierra sending unit installed, I ran a jumper from the ground of the Sierra sending unit to the ground terminal showing, approximately 4 in. The gas gauge showed a dead short, pinning all the way over to full. It is possible the float stem of the sending unit touched the bottom of the tank. I am reviewing that before I reinstall.
There may have been a flash. The tank got hot. It was still warm the next morning.
Thank you for your insight.
Edited at 8:05 pm EDT.
 
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DWABoat said:
Assuming the accuracy of the events, this is very interesting. We know the vapors from the fuel actually burn, not the liquid. Fuel flashes off/evaporates at a much lower temp than water. If the fuel sender was wired such that it heated to the minimal temp to ignite the fuel vapors, as long as the pressure did not build in the tank, and the tank temp stayed low enough, it could have “quickly evaporated” the fuel.
I have read all the postings and believe this could have happened, but the sender would have to have been wired with some type of low level dead short - not enough to burn a wire, burn a fuse, or trip a breaker, but enough to generate enough heat to ignite the evaporating fuel.
My take away: with our old, previously owned boats (like my 1989), always verify electrical wiring when replacing parts since we don’t know what was done before.
Great story. Useful info. Keep us posted.
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Missed your post. Thank you.
 
9F6E7FB4-E6E1-4771-8AC5-6B4542A0A918.png
Like any disaster several factors must come together before the big demise. (Think perfect storm).

It seems the OP was one factor away from no return. This is all very frightening. It reminds me of TWA 800 in New York.



https://en.m.wikipedia.org/wiki/TWA_Flight_800
 
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Conditions sort of like how a incandescent light bulb can get hot enough to generate light and heat, but not enough to burn out - until the glass cracks and air enters.

Maybe I should change my old aluminum tank to a new poly-tank?
 
FredM said:
View attachment 94068
Old sending unit and new damaged sending unit
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You said your gauge was spiked. Is it possible it was hooked up backwards?
I have to admit that this thread has a lot of interest for me. I had repaired and refinished the fuel tank in our boat in the spring along with much of the wiring. I installed the identical sender you had problems with and was actually disappointed with it's quality. The screws that adjust the height of the arm put a lot of stress on the plastic potentiometer body. The screws also appeared to be long enough to damage that body if overtightened.
The original sender was grounded through it's body which grounded the tank. I assumed the new unit also grounds to the tank but will have to recheck that now as our tank may not be grounded with this new unit.
There was also a single bonding wire from the tank to the filler neck but the bonding system ended there and does in the manual as well. It is not tied into the through hull and transom assembly bonding circuit. It functioned great for the 70 hrs we ran it this season but maybe we were just lucky. Going to be a priority on the winter repair list. I took a pic of it before putting all the covers on.
Would hate to have a problem like yours while out on the water.
IMG_2030.JPG
 
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The amount if current to make the gauge work is very small a few milliamps. A tank must also be grounded to make the sender work. Hooking up an additional ground is useless.
 
Bt Doctur said:
The amount if current to make the gauge work is very small a few milliamps. A tank must also be grounded to make the sender work. Hooking up an additional ground is useless.
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I think we can agree adding a ground didn't cause this. It would take a pretty high amp 12 volt circuit to create enough heat to flash the tank. That would lead me to look at the starter wiring and if there was a frayed AC extension cord in the bilge at the time (some of the OP pictures have what looks like an AC cord in view). Since the OP said it happened when he was cranking the engine......I would start there first.

Fred....don't waste your time chasing the ground issue. We need to find the ignition source or it could happen again.
 
FredM said:
The aluminum tank also acts as a diode due to its resistance, meaning it keeps voltage flowing in the right direction. When I added a jumper from the ground of the sending unit to the ground terminal of the gas tank, I bypassed the resistance barrier of the gas tank. Voltage flowed backwards thru the gas tank and heated it up.
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Where did you get this idea? You have posted this statement twice now. I know quite a bit about electronics and this is just not possible.

Several unexplained theories here...
 
FredM said:
The aluminum tank also acts as a diode due to its resistance, meaning it keeps voltage flowing in the right direction. When I added a jumper from the ground of the sending unit to the ground terminal of the gas tank, I bypassed the resistance barrier of the gas tank. Voltage flowed backwards thru the gas tank and heated it up.
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I would like to know how a aluminum gas tank can act as a diode and how voltage flowed backwards. Voltage, current what ever you want to call it is going to go to ground period in what ever direction that may be, up, down, sideways and no way a aluminum tank can ever act as a diode, someone is feeding you a lot of bad info or your on a really bad web site!!
 
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PlayDate said:
I think we can agree adding a ground didn't cause this. It would take a pretty high amp 12 volt circuit to create enough heat to flash the tank. That would lead me to look at the starter wiring and if there was a frayed AC extension cord in the bilge at the time (some of the OP pictures have what looks like an AC cord in view). Since the OP said it happened when he was cranking the engine......I would start there first.

Fred....don't waste your time chasing the ground issue. We need to find the ignition source or it could happen again.
Click to expand...
I'm having similar thoughts. There are only 4 wires involved, gauge to sending unit and the 3 wires hooked to the tank ground tab. I'd follow all those, what they been rubbing on? Where do they lead to? Remove those wires off the tank ground tab and run a temp good ground to it, then see if gauge works correctly.

OP said he was cranking the engine when he heard boiling so he shut the key off. That should have eliminated any power to the sending unit. He said hot gases were still being forced out the tank vent so he shut down all power, I'd think that means turn off battery switches, it sounds like that stopped the tanks from boiling. I wonder if he was on shore power at the time?
 
My favorite way to test conjecture is to ask the question, "Could I even do that if I tried?" I put a 500 watt, 12 volt electrical space heater above the passenger's feet to avoid having to do the plumbing of hot water heat. It produces a glimmer of warmth, the item was checked off on her agenda, and I never heard about it again. However the math never favored restarting the engine if it were aver actually used, drawing 41 & 2/3 amps at 12 volts and increasing amps as the battery dwindled (eg, 50 amps at 10 volts). Takes 6 or 8 gauge to even get those amps to the appliance. In the '50s sci-fi, the boy heroes would discover a way to release all the energy in a car battery instantaneously, rivaling the newly discovered A-bomb. Our original poster may have discovered a way to release all the energy in a marine gas tank. The directions on your pot pie tell you not to even try heating it in 10 min if you have less than 1000 watts available.
 
marty51 said:
That's a good laugh from the past.
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UPDATE:
ARMINIUS- GREAT COMMENT-
I have currently contacted my closest Sea Ray dealer, Veethree Electronics ( maker of sending unit),
and Sea Ray Corporate technical support. Veethree said it was impossible for the sending unit or the float stem of the sending unit to create a spark inside the tank. My SR dealer had no knowledge of any such incident.
Waiting on SR TECH SUPPORT.
 
I can clear up this mystery licity-split. Never happened. You're welcome.
 
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From an electrical engineering point of view, not an electrician...very different:
Fuel sending units work by resisting the potential of ground.
Aluminum does not act as a diode.
Positive voltages seek ground traveling the path of least resistance.

Survey says: Fake News
 
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