Diesel Fuel is migrating between tanks

[SV Someday Came]

Last weekend -- for the first time in a over a year -- I took my boat out!! The bowsprit is done. The bow area / fiberglassing is done. The entire electrical was just completed last Friday. The roller furler is rebuilt. The 765,023.5 coats of varnish are all dry. The new gauges are installed. The bilge pumps rewired. Ahh..... the pictures are things of beauty!!!

Last weekend was a MOMENTOUS occasion. We took the boat out. Everything worked. More on the mistakes later....


I have one fuel guage and one switch to toggle back and forth between. For the past year, the starboard tank has always had about a third of a tank and the port tank always had a little bit less. Now that the boat has been out twice, (did it again yesterday late afternoon to see what the sea looked like with a setting sun) the starboard tank now has 3/4 a tank and the port tank has barely a quarter tank. What the heck???????????????

What is causing my fuel to migrate between tanks???


Went out for maybe 20 min on a starboard tack. Then 20 min on a port tack. Then downwind level into the channel for maybe 20 mins.

I feel like I am going craZY.

If I take the boat out again, at this rate, I will run out of diesel in one tank!!


Please help.

Thanks

Michael

[GordMay]

Fuel Return Lines:
On vessels with multiple fuel tanks and a fuel system that returns fuel to the tank (such as fuel injection), the system shall return unused fuel to the same tank from which it was drawn.
Failure to do so can result in overflow.
When you use the port tank, and the excess returns to the starboard tank, resulting in the noted transfer.

[Chief Engineer]

I agree with Gordo.

Check your fuel circuits....supply/return and check and see if you have a crossover valve between tanks

[SV Someday Came]

Ok, this is serious. I have learn what is going on with my boat. The fuel in one tank is getting less and the fuel in the other tank is increasing. When we did the rewire, I did move a valve assembly -- and during the re-wire, I turned the valve back and forth to work around it until I just relocated the whole thing up and over an inch. But I forgot to note what position it was in to begin with.

I have attached a photograph of the fuel system. Anyone who saw the early "pre" wiring photograph on the Willard will be amazed at the utter transformation of the wiring system!

The fuel comes in on the lower left -- and those valves are in the correct position. I never did mess with that assembly. It comes into some small box and that box is wired into a toggle switch that is just above and to the right. I am not sure what the switch does -- since I have taken the boat out, I have not turned "on" the switch.

Suggestions?

And don't take me to task for that blasted coax dangling -- it is now secure!!

That large fuel line loop by the blue filter is the return fuel line (so I was told). It goes up into that valve assembly and that is the assembly I messed with and moved during the rewire.

I do not know if that valve gate is in the original position the way it was when I first got the boat.

I was told that the boat was set up to draw equally from both -- and it was (I know cause the boat was chartered alot in my first few months of ownership, hence I know it is something I did).

[Chief Engineer]

It looks like the fuel is coming into an electric fuel pump...to filter....the valve to the right looks like the return line. Probably what is happening is that the fuel in the return circuit is taking the path of least resistance. Therfore filling up one tank.
You will probably have to run on one tank and return to the other for a while unless you have a crossover at the bottom of each tank.

[SV Someday Came]

Originally Posted by Chief Engineer

It looks like the fuel is coming into an electric fuel pump...to filter....the valve to the right looks like the return line. Probably what is happening is that the fuel in the return circuit is taking the path of least resistance. Therfore filling up one tank.
You will probably have to run on one tank and return to the other for a while unless you have a crossover at the bottom of each tank.

Let me get this right: I keep using the system as is, and when the tank is dry and the other one is filled.... then what? How do I access the full tank? Is that valve in the right position?

[SV Someday Came]

What happens if I over- fill one tank -- where does the excess go??

[Chief Engineer]

Mark one valve port/one starboard for supply
Mark the return lines the same way.

If you want to transfer fuel from the stb tank to port tank
open stb supply valve close port supply valve.
Move arrow to direction of flow points to port tank.
If you over fill a tank it will come out of the vent

[Chief Engineer]

Did you check to see if you have a crossover between tanks?

a hose that goes between port and starboard tank that usually has one or teo valves.

[scotte]

Sorry if you already explained this and I missed it - but the blue valves on the left - is one from one tank and the other from the other tank? If both are open at the same time, then is that what's equalizing the fuel between your tanks.

[Chief Engineer]

That will not equalize the fuel between the two tanks.

[SV Someday Came]

That valve is in the wrong position as it is now. One tank is increasing. The other is decreasing. That is an observable fact marked over two hours of engine run time. And the other fact is that this shift in fuel did not happen prior to the rewiring job, hence I moved the valve position.

To make matters more confusing, I am not sure if both tanks are being equally drained. And I sure as hell do not want to spend 90 bucks an hour to have a mechanic come and look at the set up.


I am going to mark the position of the fuel tank gauge for port and starboard. Then I am going to start the engine and let it run. Then I am going to switch the valve direction and see what happens to the fuel gauge. This simply cannot be all that mysterious.

I want to go out this weekend, but it is insane to go out and "run out" of fuel with no way of knowing how to get fuel that is there to the engine!


Michael

[Chief Engineer]

MV.....apparently you do not grasp what is going on with your fuel system.

Per your photo and the valves in those positions
you are pulling fuel from both tanks
and attempting to return to both tanks

The fuel return will take the path of least resistance....head pressure

Pull fuel from the fuller tank and return to the less full tank.

You apparently do not have a separate crossover betweeen the two tanks
as you did not respond to that query.

If you don't want to pay for a mechanic to look at your setup
listen to the other posters here.

[SV Someday Came]

Originally Posted by Chief Engineer

MV.....apparently you do not grasp what is going on with your fuel system.

That is an understatement! Ok, been in the compartment this weekend. I think I got it squared away. Appreciate the effort of folks to post and help me out. I did not get a chance to completely try out the fix, but I am nearly positive I reversed the flow switch causing a backpressure to flow along the path of least resistance.

Thanks!


Michael

[Chief Engineer]

Sometimes, we look so hard at a situation, we can't see the solution.

That's when I take a break topside...have a cuppa and a smoke....and clear my head...Sometimes I even have to sleep on it.

Label Label Label...color color color....arrows arrows arrows...

Try to set it up so any one on the crew can do it...i.e. adjust valving