the fuel crossover line:

Last night my Western Star died, turned out the passenger tank was empty. Mechanic said: this truck does not have a crossover line, only two return lines. So my question now is; I guess I always need to fuel up both tanks, and from what tank is it pulling fuell then?
Driving now two month with this truck , always was fuelling driver side tank. To tight to get hose to the other side between day cab and back wall of the flatbed.
Why would they build systems with no crossover lines ?
I'm confused.

 

All modern trucks are duel draw and dual return with dual tanks regardless of size. You should always fill both tanks the same, however on a normal functioning system the tanks should level both while running and while setting over time. When you have line blockages or plugged tank vents the levels can become off causing uneven tank level, both during operation and while setting.

Crossovers were eliminated due to road debris commonly knocking the lines or valves off and causing fuel spills and leaks .

 

Even with the older bigger crossover lines we had in older rigs how does the return work? Does it pull from one tank and return to the other tank and thats how it keeps all your fuel warm?

 

"Back in the old days...." fuel did not get so hot as it does today with the much higher pressure fuel systems. Engine coolant was run through a piping system inside the fuel tanks.
Also "back then" each manufacturer kinda had their own idea of how the fuel piping would be run. Really was'nt so much of a standard like today where so many models are just body work over the same chassis. So fuel could've been drawn and returned any number of ways.
Liquids such as water or fuel will always attempt to reach perfect equilibrium. So if you have for example a two tank system with a crossover line, and the suction line is tee'd and the return line is tee'd, the fuel level in each tank will stay equal. If you shut the cross over line off, and filled one tank only but left the working lines tee'd, the return line will fill the empty tank as it has less resistance until each tank is level with each other, then begin to fill each equally.
If you leave the cross over line open, but it is a 1" line and you fill one tank with a 2" hose, the cross over can not handle as much volume and will take time to reach equilibrium with each other, but they will. So when the 2" line shuts off, wait a few minutes, then start it again.

 

Fuel got plenty warm on the tank it was returned to back in the day. At idle an old Cummins NH 220 would return it hot enough to have vapor come out of the vent. The tanks would be hot to the touch. My NTC heats it up pretty good to. Steps on Steel tanks were shin burners. Harder to tell with aluminum tanks because they are better heat sinks.

 

Technically all fuel should get to engine temp as it runs through a mechanical component that is physically connected to the engine block. Anything bypassed at pressure would then have that work heat absorbed too. But I don't recall there being a fuel cooler in the line like there is today.? I do recall however the comradery among the "truckers" back in the day. Remember when CB radios were the weather report, the traffic report and the emergency contact?