Fuel tanks uneven, cant seem to figure out, Help

Then u have something in you're fuel lines remove lines up to splitter valves in the chassis by cab bags check both splitter valves blow air and see if something comes out something has to be plugged

 

I've Found Anything From Truck Paper Ads To Hay And Dirt In These Lines And Valves Some From Bad Fuel Other From Other ####### Drivers Even Found Butter Finger Bar Parts Of It In One Line So Check In And Out For Both Valves And Lines If In Supply Line Going To Engine Truck Would Loose Power So It Has To Be From Tank To Valve Either Supply Or Return Or Valve Itself

 

What we use to do is advise the driver to let the fuel tank run low, bring it in then remove the return lines and fittings from the unit checking every connection. run the unit with the fuel return lines open and see if one is flowing a lot more, if that is OK then you have to check the suction side, every fitting and hose being sure they are all free flowing. you have to remember that gravity works, so if one tank if filed more than the other it will draw fuel from that tank more than the other, hoses length do not matter. We had trucks were the right tank was forward and the left tank was all the way back, he never had a problem.
I have found plastic bags in the tanks and those little foam ear plugs, sticks, and rubber folded back from hoses, also plastic hoses with a bubble inside in the hose.
We had one driver come in complaining about the truck leaking fuel out of the tank, I got his address and he had the truck parked on an angle when it was explained to him about gravity and the fact the fuel will flow up and over until it is level he took his loader and leveled the parking spot.

 

If the problem is new and nothing was changed, then there has to be a restriction in there somewhere. Did you blow air both ways? Sometimes the rubber deteriorates internally and acts like a check valve when you get a piece flapping. I have seen some that blow through good 1 way and not so good the other way. I have some extreme ones that blew rubber chuncks out when I blew through it.

It is easier to draw fuel out of a full tank (it doesn't have to lift the fuel as high), so it wants to draw more out of the tank with more fuel unless there is a restriction. On the return side, it's the same thing, it is easier to return fuel to the lower tank, but only if the return tubes are submerged. Together, the draw and return can compensate better for minor restriction differences than the draw alone.

I fixed one once where someone replaced a line that was about 1 foot longer, it had a hump in making a trap and it was pulling fuel uneven. A longer line has more restriction than a shorter line, a 90 degree fitting has more restriction than a 45. You want things the same left and right to make restrcition as close as possible left to right.

You could also try a sight glass on the suction side lines to see if you're getting any air from one side.

 

Mine pickup from the bottom of the tanks and return to the tops. Driver side was staying full and would actually run over if I wasn't careful. Return went through the top and both returns were working. When I turned valves off at the tank, on pick-up lines, I then removed the lines and turned valves on. Driver side wouldn't flow as much, even after cleaning, but still flowing enough fuel as to not be a problem. After hooking lines back up I opened the valve on the passenger side only half way and the one on the drivers side all the way open. Have been running like that for a couple of years now with no problem and tanks stay mostly even unless I park on a slant.

 

I have the 1 valve on the top of each of my tanks. Last year my drivers side was filling and the pass side was emptying. I tried turning off the drivers tank valve, which made it worse, it overflowed. I closed the pass side half way, opened the drivers and it stopped overflowing.
The way mine seems to work is the valve on the low tank needs to be restricted as needed to adjust the balance. Its hard to wrap your head around it because its seems backwards to close the valve on the low tank.

 

Replace both suction and return lines to the tee fittings and make sure that both suction lines are the same length and both returns are the same length. When routing the lines make sure that both left and right sides are identical with no droops in the line (the droops collect water and freeze int he cold climates, don't ask) you say that you replaced both vents which is good but also make sure that the lines hooked to them are clear ( I found mud wasps in them before)! Also check the fittings on the tanks and tee's carefully for splits/ damaged flares....yes I have seen that!

 

There seems to be different approaches, it depends on what you have time for.
My left tank valve has been partially closed for a long time, its good to know what to check.