Water in Fuel Tanks

[4129R]

It would be great if you could isolate it to one tank, by disconnecting the second one.  It could be a step toward figuring it out.  Is there any way to see the water in the tank?  You could just isolate them and have a look after a big rain storm (conceivably).  I don't know if you could try to run it on only one if you wanted.  Probably.

I can easily isolate 1 tank at the T piece which is a copper/brass compression gas T.

There is no way of knowing if there is any water in the tank until you drain it, then in a see-through container, you can clearly see the two liquids with a line where they meet.

[SilverBeast]

It would be great if you could isolate it to one tank, by disconnecting the second one.  It could be a step toward figuring it out.  Is there any way to see the water in the tank?  You could just isolate them and have a look after a big rain storm (conceivably).  I don't know if you could try to run it on only one if you wanted.  Probably.

I can easily isolate 1 tank at the T piece which is a copper/brass compression gas T.

There is no way of knowing if there is any water in the tank until you drain it, then in a see-through container, you can clearly see the two liquids with a line where they meet.

Can you poke a tube down to the bottom of the tank and draw some fluid from the bottom, which will be mainly water without having to drain the tanks? That way you could try isolating both tanks. You could possibly leave them empty and hose down the car and see if any water gets into one of the tanks?

Could the water be going round the seal round the filler neck in the bodywork, and getting inside the rubber hose from the filler neck to the tank from the top?

[4129R]

Can you poke a tube down to the bottom of the tank and draw some fluid from the bottom, which will be mainly water without having to drain the tanks?

A. Much easier to drain the tanks through the drain plug, just jack the back up, which gets all the water to run to the front where the drain plug is located. That way, all the water comes out.

 That way you could try isolating both tanks. You could possibly leave them empty and hose down the car and see if any water gets into one of the tanks?

A. I will remove the filler tops and the rubber hose connector to the tanks, and introduce resin to fill the tops of the tanks completely, through the 3" hole in the bodywork. 

Could the water be going round the seal round the filler neck in the bodywork, and getting inside the rubber hose from the filler neck to the tank from the top?

A. The hose connector is new and a tight fit, so no water can be getting into the tanks through the filler necks and caps. It must be getting in through the tank tops

[4129R]

I have been giving this a lot of thought.

If only one tank is leaking, there will be more water in that tank, water from the bottom of that tank up to the outlet pipe, and half the amount greater than fills up to that outlet pipe, with the other half flowing through the connecting pipe to the other tank.

If both tanks are leaking, and one is leaking greater than the other, I will only find this out after I seal the top of the leaking tank, or the tank that leaks more.

The right hand tank had more of the 1 pint in it, (there was very little in the left tank) so I will start by sealing the top of the right hand tank.

I further deduce that to fill an empty tank up to the outlet pipe needs just over 1 pint, which seems about right.

[Kendo]

You might consider mixing in micro balloons to make the patch lighter and stiffer and less runny, if that would help with application.

[Fotog]

If you haven't done so, how about just draining the tanks dry, isolating them, and see what happens when it rains?  You don't need to drive the car, right?  I would imagine only one is a problem.  Then take it out.  inspect it carefully, then if necessary test it with compressed air (not much, like from the exhaust of a vacuum cleaner) and a bubble solution to find leaks.  Need to plug that little breather nipple on the inlet, of course.

[GavinT]

If only one tank is leaking, there will be more water in that tank, water from the bottom of that tank up to the outlet pipe, and half the amount greater than fills up to that outlet pipe, with the other half flowing through the connecting pipe to the other tank.

Unlikely that both tanks would present as leaking at the same time IMHO.
If I've understood this correctly, yes, but I'm not sure what you mean by "fills up to that outlet pipe".

But interconnected tanks will certainly syphon both ways.
F'rinstance, assume there's, say, one pint of water accumulated in the left tank while the car has been parked over night.
(OK, technically, it'll start to syphon immediately the rain water starts to get in.)

If you now park the car on the right side of the road, you'll find the water has syphoned itself to the right tank. This assumes there's a reasonably steep crest in the road.
Similarly, if you then move the car to the left hand side of the road (facing the same way) you'll find the water has moved back to the left hand tank.

I recall going to a BBQ somewhere and parking on a slope. When I later stepped into the car to go home, I noticed the fuel was low but rose back to normal along the way.

There's also "Water Finding Paste". Our guys used this stuff to keep track of water ingress to an underground fuel storage tank we had, back in a past life.
Here's a link to an Oz product (and demo) but it must be fairly common.

https://www.fuelequipmentspecialists.com.au/water-finding-paste/