240 gallon tanks only holding 170 gallons

so you fuel your truck by the gauge. i just look in the tank hole as im pumping. if you go solely by the gauge. you will be on the side of the road fast

 

I'm going to asked this well because.

are BOTH tanks THE SAME SIZE..?
Some trucks will have a 120 on the drivers side and a smaller say 80-90 on the passenger side

If the tanks are the same size. You could have a bad vent.
Next time you fuel fill 1 tank at a time and see if they both take the same amount.... remember your gauge is only reading ONE tank.

 

Don’t change the fuel gauge on your dash just yet. Several things could be causing a misreading, including a bad fuel level sensor (as uncleal13 mentioned) or perhaps the fuel level sensor moved out of position and is giving a bad reading.

 

The tank won’t hold the full capacity unless your tanks are turned so the fill hole is right at the top.

 

There is nothing wrong with the gauge or the tanks, the tanks are not meant to be filled to capacity.

AND if you fill them up too much, you can bend the fuel gauge arm causing to to read wrong.

 

My fuel tanks are just like what dosgatos posted. I cannot move the fill hole to the top of the tank because the air vent will be moved sideways and probably cause a fuel leak. Apparently these cylinder shape tanks are correctly aligned if the air vent is exactly above the tank. The manufacturer pretty much is forcing everyone to never completely fill the tanks. My tanks say to leave 5% empty space. My guess is that temperature variations can cause the fuel to expand or contract.

 

Not sure if serious or just trolling.....

That capacity is from a bone dry tank to full. Willing to bet you still had 15-odd gallons in each tank and then left space for a few more gallons up top.

 

Depends on how you order your tanks. I had some built for my FLD that had the fill hole and vents on top. I wanted the fill hole to be on the top for a cleaner look on the tank when mounted.

 

The most my Freightliner tanks ever took, was about 226 gallons, though tanks are 140 ea. 280x 95= 266. So it will run out of fuel, with 20 gallons in each tank. My old WS could be ran down real low. The pick up was lower. You can adjust the float. Best to leave it alone. Don’t need to be running out of fuel. Both my tanks on my current Truck were turned a bit. The most it would ever take was 190 gallons, and would run out of fuel with 40 or more gallons in each tank. Had to loosen them and turn both, to proper location, vent on very top of tanks.

 

First thing to do is to stick the tanks before you fuel, to give an idea what's left before you fill. Sending unit can be bad, gauge can be bad, but the stick will always be right.....