Diesel injection system return line ?

Need to get old truck running.
Diesel tank rotted out.

I'm planning on a temporary ten gal tank in the bed.
Supply is no problem.
I know the return always goes back to the tank,
But can I tee the return into the supply?

I'm thinking that it would probably cause back
Pressure on the return and kill the engine.

Otherwise I will have to put another bung in the tank.

Thx
Tom

The return line needs to go to the tank to cool the fuel
and to ensure air gets purged.

Why not temporarily run a hose back into the fill hole on the tank? Or then adapt the filler cap to accept a hose?

TGP, what is "back pressure"?

That's most likely what I'm going to do.
I didn't think a T would work.
Thx,
Tom

(quoted from post at 18:24:18 01/14/19)
TGP, what is "back pressure"?

Click to expand...

Thinking the supply line with a T wold not allow the return to flow fast enough causing pressure to build in the return.

Backpressure is a term used to describe pressure opposed to the desired flow of fluid in a system.
Tom

I use a separate catch can if needed for the return, it COULD go to the inlet, BUT if there's any air in the return line you DON'T want it going into the injection pump. What engine/injection pump does the truck have? And when did it last run? If it's been awhile the injection pump MAY not work due to stuck internal parts. If inline pump, and rack is stuck by just one stuck plunger, engine COULD start and run away/overspeed IF rack is stuck in fuel on position. If stuck in no fuel position engine won't ever start..

(quoted from post at 19:21:39 01/14/19) I use a separate catch can if needed for the return, it COULD go to the inlet, BUT if there's any air in the return line you DON'T want it going into the injection pump. What engine/injection pump does the truck have? And when did it last run? If it's been awhile the injection pump MAY not work due to stuck internal parts. If inline pump, and rack is stuck by just one stuck plunger, engine COULD start and run away/overspeed IF rack is stuck in fuel on position. If stuck in no fuel position engine won't ever start..

Click to expand...

Thx.
Hoped you chime in.

Bosch VE pump Cummins 6BTA

Ran up to just a few weeks ago, but tank is so rotted it can't hold fuel.
Just trying to run it to get it home.
Plow truck should tell the condition of the tank.

Thanks,
Tom

I've used a gallon jug with fuel right next to engine on Dodge trucks, then both inlet and return can go into the jug. The Bosch VE doesn't like a lot of air either.

Also be aware if the VE pump has high miles it's wise to have the pump plunger return springs replaced during reseal repair. When one spring breaks, engine will suffer high speed miss. When BOTH break pump MAY be wrecked bad enough that the plunger foot will break too. Anytime I have a VE down I replace those springs.

(quoted from post at 17:20:57 01/14/19)

(quoted from post at 18:24:18 01/14/19)
TGP, what is "back pressure"?

Click to expand...

Thinking the supply line with a T wold not allow the return to flow fast enough causing pressure to build in the return.

Backpressure is a term used to describe pressure opposed to the desired flow of fluid in a system.
Tom

Click to expand...

Pascal's law says that pressure is the same in all directions. It knows no backwards or forwards.

Depends on the fuel system and flows on whether or not you can tee back to the lift pump inlet. On a common rail fuel system the lift pump supplies high pressure fuel pump and most are inlet metered (the restrict flow through a fuel control valve on the inlet side) to maintain rail pressure with lots of fuel maps and algorithms. The excess lift pump flow generally goes back to tank. Some flow goes to cool the HPFP an injectors and picks up some heat. Depending on the injector design you have some injector spill which is scalding hot but on some of the newer systems they have ZSL (zero static leak) injectors which barely have any spill at all. Depending on the lift pump flow and how much cooling flow for pump and injectors and injector spill going back you might be able to get away with a tee back to inlet of the lift pump. Priming after a filter change becomes an issue because there is no way to prime the circuit without having to open the line at the HPFP inlet to let air escape. You can use a bleed orifice in the filter base or at the hpfp inlet to let air out and send that back to tank along with the hot fuel from pump and injector cooling and injector spill. Recirculating excess lift pump flow on engine will do wonders for fuel system component life but will shorten filter life as you're actually getting the dirt in the filters instead of passing it through.

If it's an older pump and nozzle system you can just recirculate fuel but still have the same priming issues.

Unit injector systems really need fuel to go back to the tank to cool off or will need a good fuel cooler.

(quoted from post at 21:42:33 01/14/19)

(quoted from post at 17:20:57 01/14/19)

(quoted from post at 18:24:18 01/14/19)
TGP, what is "back pressure"?

Click to expand...

Thinking the supply line with a T wold not allow the return to flow fast enough causing pressure to build in the return.

Backpressure is a term used to describe pressure opposed to the desired flow of fluid in a system.
Tom

Click to expand...

Pascal's law says that pressure is the same in all directions. It knows no backwards or forwards.

Click to expand...

I can follow your (Pascal) Theory about pressure,
But what happens when you have flow in the proper direction at 10psi.,
And introduce flow in the opposite direction at 20psi.?
Won't the proper flow direction stop and go back the other way?
Causing a problem.
Tom

(quoted from post at 21:20:52 01/14/19)

(quoted from post at 21:42:33 01/14/19)

(quoted from post at 17:20:57 01/14/19)

(quoted from post at 18:24:18 01/14/19)
TGP, what is "back pressure"?

Click to expand...

Thinking the supply line with a T wold not allow the return to flow fast enough causing pressure to build in the return.

Backpressure is a term used to describe pressure opposed to the desired flow of fluid in a system.
Tom

Click to expand...

Pascal's law says that pressure is the same in all directions. It knows no backwards or forwards.

Click to expand...

The return line on my Ford 9000 tees into the suction line from the tank. It is nice to have warm fuel going into the tank in cold weather, but if there is air in the line there is a bad problem that needs to be resolved. The fuel in the return line is under low pressure,

I can follow your (Pascal) Theory about pressure,
But what happens when you have flow in the proper direction at 10psi.,
And introduce flow in the opposite direction at 20psi.?
Won't the proper flow direction stop and go back the other way?
Causing a problem.
Tom

Click to expand...

The return line on my Ford 9000 tees into the suction line from the tank. It is nice to have warm fuel going into the tank in cold weather, but there is no air in the line because we know that the motor won't run with air entering the system. The fuel in the return line is under low pressure, and when it pushes through the tee into the other line all of the molecules are then the same and know no direction. What they do know is that in the direction of the pump there is negative pressure due to the pump suction while in the direction of the tank there is atmospheric pressure to overcome, so off they go towards the pump.

T into the line on the suction suction side of the lift pump and it'll be ok.
As you said this is a temporary setup to move the truck. Once you fix the fuel tank issue you can plumb it back the way it was.
I have a 2nd gen 5.9 with the P7100 inline inj pump, the injector return is routed to the inlet side of the fuel filter and the pump return goes back to the tank.
There is not air in ether return line coming from the pump or injectors.
The primary reason fuel is returned back to the tank is to cool it during warm weather and to help heat the fuel in the tank in cold weather for better flow and less chance of gelling.
Since the engine burns some of the fuel there's alway less returning from the engine than has been pumped to it there forth returning fuel will not overpressure the suction line blocking flow to the lift pump.