Fuel Tank Mystery

[Cardamam]

Hi There! It's my first time posting to the forum, but I have run into useful advice here and hoping yall can help.

I have a 1977 44' Thompson Trawler -- had her about four years and am trying to go back and restore things and it is always a bit of a puzzle figuring out what is supposed to be there vs what unwitting previous owners have done.

My puzzle is this: I have two 400 gal tanks that are completely glassed off and have two spigots (kind of like a garden hose spigot and not like a proper ball valve) coming out of the bottom. I noticed a leak in the stb spigot, likely coming from the o-ring around the spindle on the handle. I decided to attempt a fix by replacing the whole thing, but first I needed to pump all the fuel in the stb tank into the port. I used an electric pump and could visibly see that the port tank was pretty full and the stb tank was pretty empty, but the last bit of fuel was taking much longer than it should have. To check the level in the tank I hooked a piece of clear tubing up to the spigot and opened the valve to get a visual. To my surprise, the stb was almost to the top, I checked the other side and same thing. What the heck?

There is no other access point to the tank and I'm assuming that these spigots must be connected behind the scenes somewhere. My suspicion is that there is a flow valve that closes when one tank is lower than the other and delivers fuel to both spigots from the more full tank. Is that assumption correct? Would there be a location on the boat where there should be more valves to adjust and maybe I don't have access to them because the previous owners hid it somehow?

Any help or suggestions here would be great. I think I even saw a post by a guy who worked at Thompson around this time and built the 44' boats -- I'm really hoping he is still around and could miraculously give me an answer.

Thanks!

 

[tiltrider1]

Your description is bewildering. I read it as you pumped fuel until the port tank was visibly full only to magically discover that the starboard tank was full as well. The only logical explanation is that there is a cross over pipe between the two tanks that you are unaware of or I am completely not understanding what happened.

 

[Comodave]

Welcome aboard. I too didn’t understand it.

 

[Mac G]

If your vessel is single screw my guess is tanks are joined so as you steam and burn fuel it comes from both tanks equally so you maintain proper athwartship trim and don't develop a list.
But that is just a guess as am not familiar with your vessel.

 

[Mambo42]

Welcome aboard
If both your fuel tanks were full it is obvious that you cannot transfer all the fuel from the Stbd tank into the Port tank, therefore there must be a connection between the two tanks. There is no other explanation.

 

[Bacchus]

Welcome aboard TF
I also know nothing about your vessel but was confused by your description / statements...
1. There are no inspection ports
2. You visually confirmed port tank near? full, stbd tank near empty
3. Confirmed port tank full when pumping.

I'm assuming the use of clear tubing was to attempt a quasi sight gauge... only problem I can guess at is the ambient pressure above the tank liquid is different than the ambient pressure on the open end of the tubing. If tank pressure is higher it could force a small amt of fuel into the tube and give the appearance of a full tank

I can't imagine how that would occur when you were pumping fuel out of the port tank? A clogged vent would create a negative not positive pressure when pumping.

 

[High Wire]

You can have either a dedicated crossover line or the fuel crossover occurs at the filter connections.
Can you dipstick the tanks from above through the fill connections?
Are the spigots tank drains for draining water off the bottom of the tanks? Certainly there must be tank outlet valves leading to the fuel filters? Find the filters and follow the fuel lines back to the tanks. Buy a snake camera if necessary.

 

[Portage_Bay]

I too find your description confusing. I can offer a plan that may help.

If the leak is minor do what you can to contain it, keep it out of the bilge, keep the boat from smelling like diesel. Use the boat until the tanks are much lower. If the tanks have a cross connect with valve(s) close them. Draw a vacuum on the tank with a shop vac. Open the leaker to see if you have enough vacuum to proceed with replacement.

Have all supplies and tools at hand before starting, you don't want to be running out for things trusting the shop vac to hold the vacuum.

 

[O C Diver]

First, post some pictures of the fuel plumbing as it will be easier to diagnose.

Regarding the high fuel level in the near empty tank, I'm visualizing a line between the two tanks that the spigot is teed into. To isolate the tanks there may be a valve in the line between the two tanks. Until you close that valve the fuel level you're seeing is from the full tank.

If you can't find a valve in the cross over line between the two tanks, I would wait a day and see if the tanks balance out. It that is the case, you may need to pump all the fuel out of both tanks.

Ted

 

[ofer]

could visibly see that the port tank was pretty full and the stb tank was pretty empty...............

To my surprise, the stb was almost to the top, I checked the other side and same thing. What the heck?

as we all know that's impossible unless you are introducing water into the system from somewhere.

 

[Cardamam]

Welcome aboard
If both your fuel tanks were full it is obvious that you cannot transfer all the fuel from the Stbd tank into the Port tank, therefore there must be a connection between the two tanks. There is no other explanation.

I can visually see into the tank via the deck access. The tanks started out both at less than half full. After pumping I could visually see that there was way more in the port than the starboard, but the gauge I hooked up to the outlet showed the same pressure for both spigots. I agree they are somehow connected, but if that were the case I would assume the level would equalize despite pumping.

 

[Cardamam]

Here is a picture of the set up. The only access point is from the deck fill or those spigots at the bottom. Hopefully that clears up any confusion from my description.

 

[O C Diver]

Ok, so the two tanks are together on a bulkhead. Am I correct in assuming that you transferred fuel using the fill pipes for each tank?

If it were me, I would wait and see if the tanks equalize. I find it hard to imagine there isn't more plumbing between the two tanks. It looks like the two tanks are sitting on the stringers and the previous owner glassed down to the bilge. If that's the case, the two tanks could be plumbed together from underneath. Maybe each tank has a check valve and the two spigots are plumbed together between the check valve. This would force fuel to be consumed from the fuller tank. It would also keep the fuel from transferring to increase a list to one side or the other.

If it were me, maybe I would consume the fuel until it's at a more reasonable level and then pump it into some 55 gallon drums.

Ted

 

[Cardamam]

Ok, so the two tanks are together on a bulkhead. Am I correct in assuming that you transferred fuel using the fill pipes for each tank?

If it were me, I would wait and see if the tanks equalize. I find it hard to imagine there isn't more plumbing between the two tanks. It looks like the two tanks are sitting on the stringers and the previous owner glassed down to the bilge. If that's the case, the two tanks could be plumbed together from underneath. Maybe each tank has a check valve and the two spigots are plumbed together between the check valve. This would force fuel to be consumed from the fuller tank. It would also keep the fuel from transferring to increase a list to one side or the other.

If it were me, maybe I would consume the fuel until it's at a more reasonable level and then pump it into some 55 gallon drums.

Ted

I think that is the move: to burn down the fuel to a manageable level then pump it all out to reevaluate.

I was transferring between the deck plate fill pipes (which also has access in the engine room). I have let it sit for multiple days and the level has not changed. If the tanks are connected there must be a check valve setup like you mentioned.

To me it looked like the glassed off bulkhead here was stock, but maybe that's a poor assumption? It would explain there being other plumbing behind it that is not accessible. I just can't imagine why they would wall off something that might need maintenance at some point in the future.

 

[Island Cessna]

Your original post states the problem as “ leak in the stb spigot, likely coming from the o-ring around the spindle on the handle”.
We would need a close up photo of the leaking valve to give usable advice but the valves look like standard globe or gate valves, and you describe a leak at the shaft seal or or packing. If it is packing you might be able to tighten it in place. If it is either a seal or packing you should be able to close the valve, remove the handle, then remove the seal or packing. If it is a globe valve it must be installed correctly for this to work, but it is highly unlikely to be installed backwards.
In any case be very careful not to apply any force to the spigot between valves and tank, if you break something you will have a mess. Clearly the lower the tank level the smaller the mass, so reducing fuel quantity is a good start in any case.

 

[Bmarler]

Your original post states the problem as “ leak in the stb spigot, likely coming from the o-ring around the spindle on the handle”.
We would need a close up photo of the leaking valve to give usable advice but the valves look like standard globe or gate valves, and you describe a leak at the shaft seal or or packing. If it is packing you might be able to tighten it in place. If it is either a seal or packing you should be able to close the valve, remove the handle, then remove the seal or packing. If it is a globe valve it must be installed correctly for this to work, but it is highly unlikely to be installed backwards.
In any case be very careful not to apply any force to the spigot between valves and tank, if you break something you will have a mess. Clearly the lower the tank level the smaller the mass, so reducing fuel quantity is a good start in any case.

Finally someone mentioned the valve packing. a little snug of the packing nut may just do the trick.

 

[Scrib]

That’s not enough fuel plumbing - where is the fuel return? There is nearly always a cross-over live between the tanks too. You need to do some more investigation!

 

[Greg QS]

Most likely the packing. Hold the valve with a pir of pliers. Gently tighten the packing nut. A 1/4 should do. If you in the future use the valve , good practice to loosen the packing before turning. and re tighten when closed.