Sub tank - main tank flow question

[dzrbam Lurker Find all posts View Profile Close dzrbam]

Hi all,

I've finally got my main tank installed after a few leaks from non tight clips it seems ok, however when using my main tank today approx 50km drive it transferred about 1/4 of my main tank to my sub.

I don't think it's transferring the other way though I'm not sure.

Is it normal to flow only main to sub when using sub.

[dzrbam Lurker Find all posts View Profile Close dzrbam]

This is my setup of the solenoid, but that middle hose its actually cut and blocked so im assuming thats supposed to be connected to the cut old hose on the left?

[Leethal Advanced Member Find all posts View Profile Close Leethal]

The system is designed to siphon off a portion of the fuel return to the sub tank when running on the main tank. The theory behind this is so the sub tank always has some fuel to promote using the sub tank thus keeping the internal pump functioning. When using the sub tank all its fuel return is to the sub tank.
The blocked hose should definitely be connected, I will check under mine and confirm which pipe it is connected to.

Lee

[dzrbam Lurker Find all posts View Profile Close dzrbam]

Thanks appreciate it

I understand some fuel from main to sub should flow, but in 45kms mine drained half my main tank. But then what would happen if my sub tank filled, with that hose cut and plugged.


Im guessing that cutoff hose should connect to main tank and some of the return when using main should go to the main? but im not the brightest with cars.

[glen_ep Addicted PP Member Find all posts View Profile Close glen_ep]

It's not normal for the transfer of fuel to be noticeable, and the common belief that a fuel is regularly being sent to the sub is a little bit misguided. The only specific transfer to sub "to keep the pump lubricated" occurs during engine start up. The quantity is small enough that it'd take months of never using the sub tank to make a noticeable difference.

If working correctly, the solenoid pictured will send fuel back to the tank currently in use. The rate of flow is substantial, enough so that if the system is not working correctly, you'll witness a tank transfer within a single trip as you've just explained. However if working correctly, the large flow goes back to the tank in use so you'd not notice it.

Most likely your solenoid isn't working or has been unplugged. I don't know why anyone would terminate the other hose unless it was an emergency fix after it was torn apart by a stick/branch.

I recommend testing the solenoid and then reconnecting/replacing the hose. Test is simple but risky.. unplug the blocked hose from the solenoid, which I assume is meant to return to the main tank (you can follow the cut hose to confirm). With a cold engine/exhaust (safety thing), place bucket underneath solenoid, switch to sub tank, start engine, watch solenoid - not fuel should escape. Switch to main tank - check - fuel should escape - turn engine off asap. If no pouring of fuel, then the solenoid is not functioning or not plugged in.

Finally, the cut hose seems open on the tank side. If that's not blocked it's an open hole allowing dust into the tank, and fumes out, as well as being a fire/explosion hazard.

[glen_ep Addicted PP Member Find all posts View Profile Close glen_ep]

Also, if the sub tank filled, the fuel will work its way up the filler hose and then escape down into the main tank. This can happen either direction - but it shouldn't be happening.

[dzrbam Lurker Find all posts View Profile Close dzrbam]

I recommend testing the solenoid and then reconnecting/replacing the hose. Test is simple but risky.. unplug the blocked hose from the solenoid, which I assume is meant to return to the main tank (you can follow the cut hose to confirm). With a cold engine/exhaust (safety thing), place bucket underneath solenoid, switch to sub tank, start engine, watch solenoid - not fuel should escape. Switch to main tank - check - fuel should escape - turn engine off asap. If no pouring of fuel, then the solenoid is not functioning or not plugged in.

Finally, the cut hose seems open on the tank side. If that's not blocked it's an open hole allowing dust into the tank, and fumes out, as well as being a fire/explosion hazard.

Pretty sure it was cut due to gas going in, in regards to testing im pretty sure its already been tested.

Because that clamp on the blocked of hose is the one I had to replace as that clamp (blocked cut hose) was leaking pretty bad when the car was running and i was on main tank.

So im assuming I just need to connect the 2 cut hoses together and it should work? Does that sound correct?

And yeah looks like tank side is open, damn mechanic

[glen_ep Addicted PP Member Find all posts View Profile Close glen_ep]

Eeeek wow I'm surprised the hose didn't pop right off!!

Yes just reconnect the cut hoses.

As I can't see everything in the single photo, I'll just confirm the connection and flow: excess fuel from engine bay via steel tube --> rubber hose into solenoid --> 2 rubber hoses, each leading to a tank

[dzrbam Lurker Find all posts View Profile Close dzrbam]

Thanks yeah the bloody thing was leaking, mechanics didnt connect to cut hose just put better clamps :/

After another trip to mechanics,

Now its set 1 hose to engine from solenoid and 1 hoses from solenoid to each tank.

The one that leads to main tank is rubber from solenoid then it appears to change to a metal hose or Atleast a bit smaller hose.

If you check my photo on the centre/main hose where it's cut on the back side (old hose) you can see where it gets a bit smaller.

[glen_ep Addicted PP Member Find all posts View Profile Close glen_ep]

Yep I can just make out the steel tube on the left side. They prefer to use steel tubing as much as possible for high pressure lines (fuel and brakes) but the rubber sections are still necessary in some places. Particularly when connecting between chassis mounted objects and body mounted objects.