95 Peterbilt 379 fuel leveling problem

To be completely honest, first truck I ran was a 1989 Peterbilt 379, it was great back when they still put the bottom crossovers, and it was bottom draw as well. My 1997 had the return valve up top of the transmission. Always had issues with leveling off, swapped the vents, swapped the valve etc. finally said screw this and added a bottom cross over like the 1989 and never had an issue again. You can try cleaning your vents, see if that helps. If not maybe go the route of a bottom cross over.

 

Like mention already, clean the vents/breathers. Been there done that.

 

I had a 1994 379…… it did the same thing.

 

Also you need to make sure that all lines to the cross overs whether suction or return are the exact same size, length as well as pitch or angle. Be surprised what a difference 2 inches in suction hose length will do for draw. Making sure you’re not sucking a little air there is paramount too. I have just a slight abnormality in the hose usually right at the fitting cause trouble too. A partial blockage on suction or return will ruin your day

 

My 1998 did the same,bottom draw, top return, cleaned vents, checked everything, replaced the splitter valve ( theres nothing really in them that can stuff up, a spring and a butterfly plate), ended up putting a tap on the left return line at the top of the tank, half turn of it and it balanced out better, ended up putting a crossover off the bottom taps, pull up at the pumps and the left tank still takes 30 litres more than the right tank, same size tanks, crossover definately helps