All Trucks, Campers, Trailers, RV's and Motor Homes - HD Volvo D12 Fuel problem

I have inherited thid problem. This is a 1998 Volvo Semi truck with a D12 volvo motor. Someone else has already changed the fuel pump. This engine is hard to prime, and will run with good fuel pressure for about 30 seconds. Then the pressure dies and the engine slowly starts to die. I bipassed the fuel system by running a supply line right to the tank/bucket. but I had to put a return line from the original supply line to the tank/bucket because fuel is pouring out of it. But the truck runs fine???? I have taken off all the fuel lines, the ECM, and inspected tghem all for holes/leaks, debris. but found none. I have noticed that when running the engine with the original fuel lines that the fuel gets really hot... I kind of thouhgt that there is a restriction in the return but I am not sure if there is even an actual "return" line on this motor.. also I dont know what the other 2 lines that go to the fuel pump are for. One may be for priming, I dont know..

Not sure if the Volvo is like the Cummins, but 70% of the fuel pumped by the lift pump returns to the tank. It is used for lubrication only for the injector pump. Fuel gets hot due to the heating element in the fuel filter. Diesel must be heated before it gets into the combustion chamber. Your air intake also has a heater grid to heat the air so when it and the heated fuel mix, they don't have such a difficult time exploding. You may want to upgrade your lift pump to a higher volume pump. I installed an Aeromotive pump on my Cummins and it maintains a good 16psi at idle, 6 at WOT and 12 on the run.

im pretty sure the fuel is supposed to be cool as it runs back through that computer though? there is no grid heater/ pre charge air heater. I am really good with detroit diesel and mercedes. but they are all different fuel set ups unfortunately.
EX: mercedes doesnt have a fuel return. So I am still lost but is good to give me another perspective to look at, thanks Chandler.