Diesel tank leak

[William983]

I have a strange situation with a diesel tank leaking.
Diesel in the sump. Oh no. Cleaned it up. Seems to be at bottom of 200 gal steel tank. Emptied, washed, emptied. Air test. 4 lb 2 days. Hmmm no leaking. Added 2 8 inch inspection holes cleaned again. Air test. No leaking. Added fuel. No leak. Came back 2 days later gallon of fuel on the floor. Emptied tank washed, air test
No leaking! HELP!

 

[Comodave]

Could a fuel hose be weeping? Put some paper towels around where you suspect a leak and they will show the leaks. Put them all around and see which ones get wet.

 

[Lepke]

I've had leaks where a fuel line or hose wore a hole where it went thru a clamp hanger. Engine vibration over time wore a small hole. Since the hole was caused by the hanger, the hole was against it and didn't always leak. Eventually I reasoned that it leaked at night when everything was cooled down. The fuel line contracted slightly and opened the hole.
Best way to fine it is with air pressure in the line and listen for the leak.

 

[Arc]

If there is sludge in the bottom, it may pass a pressure test but not a leak test

 

[Pete Meisinger]

Sounds like a syphon going on with a fuel line.

pete

 

[fgarriso]

Try capping all of the fuel tank outlets, and then pressure test again. If that works okay try pressure testing each of the fuel lines and filters. Thake it one step at a time until you find the leak.
Dave is correct WHITE paper towels laced out everywhere will help spot the leak.

 

[William983]

I wish it was as simple as that. All fuel lines are closed. Air vent closed, fill cap closed. One day it leaks, the next day it doesn’t. Paper towels are good today, tomorrow I may need a bucket!
I left 5 # air pressure on it today. I’ll check it again tomorrow. It has baffled me. The leak comes from the bottom of the tank. Or the back and then runs to the bottom front. Next will be to fill it with water and see if that leaks out. Thank you all for your input. Please don’t stop sending ideas...

 

[Comodave]

You said you cleaned the tank out several times so I don’t think it is a layer of crap on the bottom of the tank plugging up some pinholes and they leak intermittently, but that would be my guess with the latest info you have provided. If the tank leaks when all the fuel hoses turned off then you have a leaking tank. The solution is to either replace the tank or try one of the tank sealing products and see if you can find one that works. Who knows, I have read posts that said the sealing products work and others that say they don’t. The sure fix is a new tank, but expensive. How old is the tank? Good luck.

 

[fgarriso]

Can the tank be removed without tearing the boat apart?
The pics look like the tank maybe coated with something.
If they are S.S. then no coating is needed.
If they are coated it may be hiding further problems.

 

[Ski in NC]

Pressure testing an empty tank with air is problematic. The air under pressure is partially compressed, and there is a lot of volume, it would have to be a big leak to show up as a reduction of pressure. Also, pressure reading will vary a bit with temperature changes.

When we pressure tested with air, we would hold the pressure and "snoop test" (dilute soap solution) to look for bubbles. Not practical in a coated, installed tank.

Since you have access panels, I'd look into sealing the inside. Unfortunately I am no help on the best method.

 

[Pete Meisinger]

Fiberglass fuel tanks are built of numerous layers of fiber and resin. A leak in any one area does little to indicate where the leak starts. If the glass is delaminating the fuel can trickle a long was before it escapes the tank. Although your tanks look sound I suspect they are delaminating. Please tell me the dark grey and light blue colors are a trick of lighting. If not, they are saturated and ready for replacement

pete

 

[William983]

No, it’s take out the engines or through the side. Air test again today
9:30 am 5 pounds 3 pm 5 pounds.
Tomorrow I’ll try a vacuum test.
Colors are light shading.
After vacuum test, I’ll try colored water test. At my wits end!

 

[Arc]

Carful with a vacuum test . You may make a portable tank out of it.

 

[William983]

Carful with a vacuum test . You may make a portable tank out of it.

Yeah, my vessel engineer said 1 pound should be enough.
I lowered the pressure this afternoon to two pounds in hopes too much pressure is sealing the leak up

 

[floater]

When you air test it is there fuel in the tank or are you hoping to push air out of the hole? Just wondering thanks and good luck

 

[William983]

Air test was just air. Today I put in 80 gallons of fluorescent water and 4 pounds of air. Tomorrow we will see.
I had an old welder tell me that he used to work in vessels that x rays could not find a leak in, but diesel could! Sooner or later I’m going to figure this out. Through friends daughter who is a coatings specialist for the navy, I hopefully figure out what to coat the inside of the tank with......time will tell

 

[STB]

Dave is correct WHITE paper towels laced out everywhere will help spot the leak.

I actually find that the brown paper towels, the cheap gas station kind, show leaks better. They change color from light-tan to dark brown with a drop.

Wet white somehow seems to look like dry white. At least to me.

 

[C lectric]

I have found the blue Scot or similar blue towels show even a small bit of wetness very distinctly. The white not so much.

 

[fgarriso]

If removing the tanks is out of the question then your only solution is coating the inside. That will require removing all lines, vents, and valves. Then install brass plugs everywhere . You will need the brass plugs installed so the sealer coating won't seal up the ports.

https://www.kbs-coatings.com/tank-sealers.html

 

[fgarriso]

After looking at the pics again the tanks appear to be fiberglass. If that is correct do to delamination issues with fiberglass the leaks could be coming from anywhere. The only solutions is cutting the hull sides out to remove the tanks, and then reglassing the hull. Or, sealing the the tanks from the inside. Pressure testing a fiberglass tank may not work do to the pressure sealing up the laminations

 

[Nick F]

An alternate method to paper towels is baking powder. Sprinkle under the tank. It changes colour to off-white with diesel - very sensitive.

Nick

 

[jusaplayin]

If you find your tank is in fact leaking, don't forget to include your insurance company. If it is a result of corrosion, they won't be responsible for buying you a new tank but they probably will pay to have it removed to find out. I also had this issue. The mechanic removed the tank to find out after 3 tests it didn't leak. It almost has to be a leaking fuel line. Diesel tanks do not have the check valve that gas tanks have and a leaking line will keep leaking due to syphoning. So make absolutely sure it's the tank before you extract it!

Paul

 

[Nick F]

Paul - thanks for the suggestion. However, I purchased the boat last Sept with the suspected leak listed on the survey and the insurance company had the survey, too.

Nick

 

[William983]

Tank Leak

It leaks diesel, but not air, not Dyed water.
Put it under pressure, disconnected all the lines.
But fill it with diesel, and it leaks. Soooooo
my next attack will be to sand blast the inside of the tank, and apply
a coating to the interior. Working through 8 inch holes is just thrilling!

Ill keep ya'll posted on how it works out.

 

[Marco Flamingo]

I just went through this, although I didn't bother to find out exactly where my tank was leaking, other than to make sure that it wasn't leaking at a fitting that could be repaired. The look of William's tank is the same as mine and probably the same construction. Fiberglass over steel. Apparently the idea was that the layer of fiberglass would keep the exterior from rusting and the diesel would keep the insides from rusting. Seems to work for about 40 years.

My tanks are so close to the hull that I could barely get my fingers underneath. But were I could, I could tell that the thin layer of fiberglass had delaminated. If I pushed up, the layer would oilcan and leak out somewhere, although the tank itself was sufficiently stiff that it didn't flex. This would squirt out the diesel in the fiberglass "blister." It might then take a day or two to fill the blister back up with diesel from the pinhole leak in the tank. No leaking for two days and then leaking again. Grrrr. It would also have been possible to pressure test the tank and have any bubbles or leakage hidden under the veneer of fiberglass.

I didn't have inspection ports in mine and felt that this was a project for a professional, or at least somebody with experience. If I had already had three 8" inspection ports, one in each tank section, I might have tried coating it myself. The only remaining difficulty in a DIY job is cleaning out the tank. I hired a guy who had a steam cleaner, a wet shop vacuum, and a helper. He ran them all at once and cleaned out the tank in about 30 minutes. Best part of that was he hauled the goop (and there will be goop) off to the hazmat site. That was included and took some of the sting out of the $2,800 price tag.

Since the entire bottom and up the sides 6" was coated, I don't know and don't care where the hole was. That reminds me of the scariest part. Before he put in the coating he whanged on the bottom of the tank with a steel marlinspike. He said that there was no point to coating a tank that he could punch through. My tank passed the test.

Now the question is do I bite the bullet and have the other tank done?

Good luck.

 

[Glaukos]

I would not cut the hull sides to remove a fiberglass tank. If the tank can't be sealed from the inside, cut the tank up to remove it in pieces. Replace with a tank or tanks that can fit through the engine room access points. But it should be possible to fiberglass the inside of the tank. Work through your existing access ports or cut a larger portion of the tank out to give you room to work inside the tank, then glass it back in after you have glassed the inside of the tank. The existing tank has structural strength, you just need to seal it with a layer of resin and cloth if it is, in fact, delaminating. Cut the side of the tank out to see what's going on. Fiberglass can always be repaired.

 

[Glaukos]

If the tank is steel covered with fiberglass, the method that I used to repair my black iron fuel tank may be of interest. You can see it on my Youtube channel at:

I re-filled the tank this winter and no leaks.

 

[DrissZougari]

I totally agree with "fgarriso" assessment that you can not pressure test a a delaminated fiberglass tank!

 

[William983]

2800 sounds cheap
I’m probably 700 in, and 40 hours of labor so far. Wish I could find someone to do it around here.

 

[Marco Flamingo]

Since you already have inspection ports installed, I wonder if somebody has attempted to address the problem in the past. While it is possible to put in inspection ports just for a look-see, most wait until there is an issue. You may find a failed patch job.

I was very fortunate in that my tanks were empty enough so that I could pump the leaking one into the other using the fuel polishing system (which took hours). I suspect that the tanks had not been completely full for years and I had recently filled them. It may be that I had put more pressure on the tank than it had seen for years.

Once the inspection holes were cut it was possible to put a light in and check out the condition of the tank. The bottom panel was rusty, but the sides and baffles all appeared to be perfect. The bottom plate had way more corrosion, which made me wonder if it had been constructed of a different alloy or grade. There wasn't a lot of gunk, but the 3 or less gallons of diesel remaining would have both gunk and metal shavings in it. I didn't think it was worth saving.

Pressure cleaning removed the scale and left shiny metal in some places. A steel marlinspike was used to whang on the bottom and make sure that it was solid enough to coat. If not, it was possible to reinforce the epoxy putty with steel or aluminum mesh if the area was small, but that wasn't required. I peeled back some of the fiberglass on the bottom of the tank and whanged on that from the inside. It didn't make any pimples on the outside, so it was structurally okay. But somewhere there was a pinhole leak.

One man mixed part A with B in baseball size gobs while the other applied it by hand, smearing it over the surface at 1/8 to 1/4" thick. The sides of the tank were only done up about 6 inches, as that's where the corrosion stopped completely. My prior owner had moved the fuel fills on deck because he said that water sat on them (I don't know why he didn't put in scuppers right there). So it was very likely that water had sat on the fills and if (when) the o-rings were not perfect, a lot of water would have entered over the years.