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

FredM

Member
PLATINUM Sponsor
Oct 23, 2020
39
Lake Lanier, N. Ga.
Boat Info
2012 SUNDANCER 260, Lowrance Elite 5, Venture trailor, F150 platinum,
Engines
350 Mercruiser
I have a 1990 250DA. My gas sending unit died so I bought a Sierra replacement. Then I watched a bunch of You Tube videos. I noticed the old sending unit didn't have a ground. The new unit instructions said to ground it. The main ground terminal was located on the gas tank, 4 inches from the ground terminal of the sending unit. So I ran a ground wire.
I removed some old gas in my tank. I put in 12 gal of new gas and began to crank it until it got thru the system.
I heard something that sounded like boiling. Then hot fumes started belching from my gas weep hole. I rapidly cut off all power and got off the boat until things cooled down. The entire 12 gal. was gone. The inside of my gas tank was scarred. I had created a dead short and turned the tank into an oven!
I spent 2 days flushing my tank and removing residue. I am installing a second sending unit. The 1990 sending unit was grounded by the screws to the gas tank. No ground wire.
LESSON LEARNED. Observe and follow original wiring first.
Has anyone heard of this?
 
Got em on my phone. Will compile in the next couple of days. I collected about a pint of aluminum sludge from my tank. I have the old sending unit and the new Sierra unit covered in dried Aluminum sludge. I have an endescope. I can probably take a pix of the inside of my tank.
 
Did you hook power to the sending unit?
It is only supposed to close a ground path for your gauge to function. You better check your connections at the gauge before trying it again.
 
I have a 91 250 with a mid-reading fuel guage. The water tank sits on top of the fuel tank. Did you remove the water tank and wood bulkhead to access the sending unit? This looks like a big job I not sure I want to tackle.
 
Then hot fumes started belching from my gas weep hole. I

There is no weep hole in a gas tank. Troll
 
you can see it in front of the SR about a foot below the filler. If you blow it up. THE PICTURE not the boat :)
 

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Did you hook power to the sending unit?
It is only supposed to close a ground path for your gauge to function. You better check your connections at the gauge before trying it again.
No I didn't. Just the red sending wire. Then ran a ground wire from the ground connection to the ground terminal on the gas tank. Thant's where I got a dead short.
I will test my gauge with my new Sierra sending unit before I install it.
Then hot fumes started belching from my gas weep hole. I

There is no weep hole in a gas tank. Troll
The weep hole on the outside of the boat below the gas tank inlet.
 
I have a 91 250 with a mid-reading fuel guage. The water tank sits on top of the fuel tank. Did you remove the water tank and wood bulkhead to access the sending unit? This looks like a big job I not sure I want to tackle.
There is a 5 inch high space between the gas tank and the water tank where you access the sending unit. They don't give you much room.
 
Better take it by trailer to a pro. Pull the bilge plug with the expectation your gallons of gas may come out. While a full tank is hazardous, the explosive potential of an empty tank is measured in sticks of dynamite. Residue may create enough vapor to combine with air in the optimum explosive ratio. This is a bad area in which to experiment.
 
There is a 5 inch high space between the gas tank and the water tank where you access the sending unit. They don't give you much room.
This is good news. I didn’t think there was enough space. Guy I knew pulled the water tank. I will talk to mechanic about doing replace over the winter. Besides the time almost blowing up the boat, how much time did it take you? So I can tell if mechanic is overcharging.
 
This is good news. I didn’t think there was enough space. Guy I knew pulled the water tank. I will talk to mechanic about doing replace over the winter. Besides the time almost blowing up the boat, how much time did it take you? So I can tell if mechanic is overcharging.
A sierra sending unit costs $40 on Amazon with 1 day shipment, less if you can wait. You pull the old unit out and use it as a guide to cut the new unit to size. A pair of wire cutters and a hack saw will do just fine. He probably has a cut off wheel. TELL YOUR MECHANIC NOT TO ADD A GROUND WIRE EVEN THOUGH THE INSTRUCTIONS CALL FOR ONE. He will have to bend the float wire slightly to get the unit into the hole. I am 5'10" and 155#s. I can get down in there. It will take a small guy. Now that I have done one, and am installing a new one since the first unit is gunked up with dried residue, It will take me 1 - 2 hrs max from opening the box.
Watch this 9 minute video on another Sea Ray.
 
Tracking...
 
Fred, something else must have been going on. First, the reason the new sending unit had a separate grounding wire was simply so it could be used with a plastic tank - which was mostly unheard of in 1990. Correct, the sending units bolts would ground properly into an aluminum tank like you have.

BUT... if the ony thing you did was to connect the new grounding wire to the tank's welded-on ground tab, I fail to see how that would cause that issue. A ground is a ground is a ground - all you essentially did was add another ground pathway - which is NEVER a bad thing.

Besides, even PURPOSEFULLY touching the red (actually, it should be pink) sending wire directly to the tank will NOT cause that issue. In fact, that is exactly how you test the system.

There's gotta be something else that was going on... and might still be. You should probably enlist the help of a professional on this one. When dealing with gas fumes, this is not an area where "I think I got it under control" is good enough.
 
All of that ^^^^^^^^^^^^^^^^^^^^^^^^
 
And it makes no sense that 12 gallons of gasoline would be boiled away by current coming from a gas gauge sending unit. That much current would melt the sending unit wire. And the boat would have blown up. Any heat source strong enough to boil away 12 gallons of gas would absolutely have ignited the boiling gas vapor. This all sounds very strange.
 

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