Fuel Tank Capacity

The tanks will equalize, when you are parked and the truck is on a slope to the right it will pump all the fuel to the passanger side tank, even with truck off. When running it has a equalizing valve mounted on the frame, that valve has a little butterfly flapper in it, if it wears out after time it will cause to pump more fuel to one tank, in your case passanger. I would replace that and i would also take the fuel lines off the fittings from the tank and equalizing valve and blow em out with compressed air.

Ive had this happen on my old 379 and my newer W900, the W900 was different, my right tank rotated towards the frame do to loose straps, pinching of the feed line and blocking of fuel filler.

 

You may have a fuel cross-over line on a fuel tank stabilizer rod connecting tank to tank. The cross-over line should have a shut-off valve. At the top of each tank is a breather to prevent vacuum from preventing emptying of the tank. The breather will have a tube that takes any surge of fuel to prevent it from splashing onto the visible parts of the truck. The neoprene tube may be plugged. Try to blow into it. If one tank remains higher than the other after being parked for a while, remove the cap. If the tanks then equalize, you have a vacuum and breather problem. If they don't equalize, the cross-over line or shut-off valve may be the problem. At least, that is how it was in the olden days.

 

heyns there is no more cross over line on the newer trucks, its "illegal" nowa days even though i had it done on my old Pete since it was the only way to get it working right.

 

If your fuel tanks are like most, the filler caps are not at the absolute top, but more like 7/8 up . This prevents the tanks from being filled to their full capacity, allowing for fuel expansion due to temperature changes.

Imagine filling your truck with diesel from a cool underground tank at ambient temperature, say 70 degrees, and being pumped into your truck where it is then circulated through the engine and returned to the fuel tanks at the engine's operating temperature, probably around 190 degrees. I'm guessing this temperature difference could mean a volume increase of one or two inches in the tanks, and possibly an overflow, (spill), if the tanks were totally filled with no air space. Most tanks have their capacity etched near the neck, along with a warning not to fill more than 95% of that capacity.

Also, as you noticed, the suction line does not extend all the way down to the bottom of the tank enabling the tanks to be completely emptied. This is intended to prevent any water, or trash to be picked up and carried into the engine's fuel filters.