Fuel Tank Leveling Problem

Several things will cause this. Plugged fuel tank vents(easiest to fix), restriction in the feed line or the drain line. Depending on the engine, the truck might also have a anti-flow back valve in the system, its a small aluminum block. It could also be bad causing this issue.

 

Cross over lines are no longer used to level the tanks. If it's a KW you have a valve towards the rear of the cab or sleeper between the frame rails that is responsible for levelling.

 

There is a small fuel line connected to the top of each tank. These smaller lines come from the back of the head on your engine, returning un-burned, warm fuel to your tanks. Both lines are connected with a T fitting, ideally fuel flows to and from evenly for both tanks, levels stay the same, and they found a cure for cancer. NOT! From day 1, your 98 Pete's tanks never had the same fuel levels as long as the engine is running. Going down the road, the drivers side tank level is most always lower. In addition to the fuel lines, in the top of each tank is a pressure equalizing vent which is probably the culprit. Fuel returning from a running engine will flow to where there is less resistance; i.e. lower air pressure in one side vs. the other would see all the returning fuel go to the side where the vent is working properly, while the side with the plugged up or stuck vent has a "bubble." Clean or replace both vents, thus allowing the atmospheric pressure on top of the fuel inside the tanks to be close to even. If that does not resolve the issue, you have a blockage in a fuel line or fitting; it happens! Good luck, I hope that helps.

 

I've got a similar problem on a Frlt. Could also be loose, cracked, or damaged fuel line fittings (I had a truck with a dented fitting once), trash in the line coming from one tank, or if you have tank cutoff valves, they will suck air when they get old. Could even be chafed or pinched lines.

 

CAT motors also have a unique potential problem, unrelated to the fuel tank levels but it will drive you insane trying to figure out if you don't know about it or where to look. Your power drops; no check engine light. You change fuel filters... problem goes away but returns when you least expect it. You look for pinched fuel lines, have them blown out, all is well - no blockages. Weeks go by, no problems.
Then one day, it happens. Complete fuel starvation. You change the transfer pump, no improvement. Hopefully you didn't have to be towed in. Okay enough torture. Remove the 2 bolts holding the primer pump on its housing, being careful not to tear the gasket. Better yet, get a new one and keep it in a safe place where it won't get bent. In the bottom of the primer pump, there are 2 round brown steel things pressed into the aluminum flange. They are check valves. All the fuel going into your engine goes through those valves; one faces up, the other down. If one of them gets a little loosey goosey, it can and will flip over - stopping all fuel from going through. I used to carry a spare primer pump, just in case - plus a new gasket. I once saw one of those pumps blow the plunger clean out of the housing; keeping a spare is just good PM. Make good choices! And if you are blessed with a CAT engine, be thankful and take good care of it! They don't make them any more.

 

My old ('88 w 3406C) 379 has had all the equalizer crap removed and a tee in the return and suction lines, both suction lines have ball valves in them so that you can shut off the draw from either tank, but with both valves open it keeps both tanks about the same.

 

I have a 2004 International 9400i with no crossover line for the fuel tanks. When I only fill one tank, how do the tanks equalize if all the fuel is being returned equally from the head

 

As long as there are no leaks or blockages, the tanks slowly equalize. They are connected and the tank with the higher level will siphon into the tank with the lower level. When the engine is running, it can pull fuel from a tank with a higher level easier and return fuel easier to the tank with a lower level. So a running engine will equalize faster. They call it a dual draw system and when they are working, no crossover line is needed.