Fuel tank overflow

Plugged vent or bad vented cap, not sure which Volvo used.

 

The way most all modern trucks are set up is called duel draw duel return. Suction and return lines go in the side or top of tank with down tubes. Those lines usually tee above the transmission or a cross member behind it.
Anything that cases a difference in pressure or flow between the tanks with cause this. Even a stopped up vent as mentioned.
Use the search block on the top right and ask your question in different ways. Do not limit yourself to your truck and or engine make. One fuel tank overflowing. One tank runs out of fuel. Fuel tanks not equalizing type questions. It has all been gone through before.
One of the few things required by the EPA that makes since. In the old days there was a crossover line between the bottom of the tanks. It was normally attached to a cross brace with a cut off valve on the bottom of each tank. When a deer, tire or something was ran over it could knock out the crossover and cause a fuel spill.

 

That happened to me once. I was on the shoulder, under the truck with my finger in the hole to keep the fuel in and wondering what to do next. A really nice driver stopped and whittled me a plug from a stick. He made a good plug, stayed in there for about 500 miles until I got home.
Back in the day it was very common for other trucks to stop and see if they could help when you were on the side of the road.

 

Wow!

Not only did he stop to help you but the guy whittled you a plug!

And it worked for 500 miles!

How effing cool is that!