Fuel Tank Overflow Issue

Caps are in good condition and the seal is good as well.

 

Shut the left side valve off and let it suck from the passenger side. I’ve had this problem with all three of the Paccar trucks I’ve owned.

Run it like that for a day or two and then see if it’s still acting up..

In my case I narrowed it down to running the right side tank too low and getting air in the line. Another time I believe it was from the check valve in the Davco. Was sludge/algae preventing the check valve from closing after I shut it down causing air to get into the line.

Part of my PM stuff I do when sitting bored..shut each tank valve off and let it draw from one tank at a time for a little while.

Try what I mentioned, it doesn’t cost anything!

 

That kw your truck? Check to see how close and hot the muffler is getting and how close it is to the pass side tank, on the older aero w9s the muffler is mounted to the back side of pass fuel tank for non integrated muffler in cab stacks. Maybe try just insulating/heat deflector ?

 

If all else fails, take the factory splitter valve off, throw it in the weeds and put a brass tee in its place with no restrictions for your return fuel..

 

Yeah or maybe tilt the splitter towards the driver side and see what happens I ordered 2 new vent valves. My passenger side tank has 2 vent valves and my driver side has one

 

I have the same problem on my Freightliner. Been running off one tank for a while. Could be my 3 way shut off valve. They are known for problems. Freightliner quit using them years ago. They’re also real expensive. I won’t be buying one. I like being able to isolate one tank for lots of reasons. Newer ones just use a T. If anything I’ll install 2 quality brass shutoffs and a T. Fairly cheap. I’m almost certain my problem is a blocked pick up tube. Especially since I dropped a whole small plastic bottle in it. Lol. Pretty obvious. It must have taken a while to melt and get stuck. As far as fuel cap vents, you can check them by swapping them, or just leaving the bad tanks cap off, while running. Maybe fill both a bit below full. Let it run with both caps off. See what happens. Probably same as mine. It’s not drawing from one tank, but is still returning. I’ve done all that already on mine. The only thing I can add on yours is to make sure the supply line is also routed in a continuous upward angle. Any high loop will cause it to lose its siphon. Please share the remedy when you get it working right. This is a very common problem. Especially since they went to top draw tanks and outlawed bottom crossover lines.

 

Sorry to quibble, but

49.393.65
Fuel lines. A fuel line which is not completely enclosed in a protective housing must not extend more than 2 inches below the fuel tank or its sump. Diesel fuel crossover, return, and withdrawal lines which extend below the bottom of the tank or sump must be protected against damage from impact.

Theres a little more, but thats the relevant bit, so no they arent outlawed, just not common anymore, and certain fuel tank hangar designs dont lend themselves to doing it safely

that said, of all the hangar designs, kenworth hangars offer the best protection, especially if the bottom pull/crossover is within 5 inches of behind a hangar.

 

Rideand repair touched on the problematic 3 way valves once used, as i had previously in a post somewhere as well. The valve stems seals in the valves tend to wear out from vibration and the rods hanging from them, causing a suction loss and such. Another thing to try that is easy and cheap is to leave fuel caps on, pull a vent line up from a tank, plumb a small regulator into it and put about 5 to 10 lbs of pressure on the tank for 10 minits or so. You wont hurt the thing as the caps are relief valves as well, and this will get your siphon going once more if it was lost. It will also show a leak in the return side circuit that usually has very little if any pressure on it.

 

I did that once to pressurize my system after losing prime changing an injector. I put too much. Almost 20 lbs. I heard both caps pop up and lock in. It started, ran 15 seconds and stalled. Made a mess trying to bleed all the air out. I got it down to around 5 lbs maybe? I could tell the cap was under pressure still when pushing doom it. Finally I took a cap off, carefully in case it blew off. It did, hit the bunk pretty hard. Luckily I got my hand out of the way. It works for priming. Have to be careful though. Better to just remove a cap and use a blow gun and a rag, crank till it primes and starts up. I need to pressurize mine to find the leak. I was thinking of removing the vent and putting a regular fitting in place, air it up with a mini compressor like last time. It has a gauge, and when shut off will hold the air. When done, disconnect it and the air will come right back out. Ideally fabricating a cap with a fitting, gauge, and shutoff valve would be nice to have. $$$$

 

I did that once to pressurize my system after losing prime changing an injector. I put too much. Almost 20 lbs. I heard both caps pop up and lock in. It started, ran 15 seconds and stalled. Made a mess trying to bleed all the air out. I got it down to around 5 lbs maybe? I could tell the cap was under pressure still when pushing doom it. Finally I took a cap off, carefully in case it blew off. It did, hit the bunk pretty hard. Luckily I got my hand out of the way. It works for priming. Have to be careful though. Better to just remove a cap and use a blow gun and a rag, crank till it primes and starts up. I need to pressurize mine to find the leak. I was thinking of removing the vent and putting a regular fitting in place, air it up with a mini compressor like last time. It has a gauge, and when shut off will hold the air. When done, disconnect it and the air will come right back out. Ideally fabricating a cap with a fitting, gauge, and shutoff valve would be nice to have. $$$$