1972 Low Pressure fule Pump 280 6 Cyl Gas line

[aluminum]

What is the correct*** " Gas Return Line " *** Hook up ?

Car is a 1972 MB 280 SE 6 Cil Gas Motor ( Mechanical Fuel injected )

I am getting Mixed Info and confused by such ?


The Low Pressure Pump mounted at rear of Car has several Gas Lines in and out > The Car I am working with was Wrecked in the rear so Bad I could not see the lines and had to pry out the tank with a crow bar lol and the lines where torn and damaged all apart . Car has been sitting at least 14 years ..
The Question is this :

(1) What is the correct way to hook up that low pressure Pump ? :
(2) where do I hook up the return Line ! ?


(I have looked at such cars and found them hooked up different ways ?)
Rather than the return line going to the return Line port on the Pump I see that Port blocked off with a Screw at the end of the port ( the Port is threaded for this screw ? leading me to think you have perhaps an option as to how to hook up the return line perhaps ? )

***
2 Cars I looked at have that Port Blocked off ?

( A ) And a T Fitting with the return line going into the T

( B ) Out of the T the other 2 line's go's to (B 1 ) the Pressure line going to the motor ? < and > ( B2 ) to the Gas Tank ?
( so 3 lines at the T return line feeding in and then going to the Motor and going to the tank ? seems very strange )


Found this Good Video online that show's that you hook up the return line to the return line pump inlet now that makes sense it seems but is unclear as to how the return line gets the gas returning to the gas Tank
( Note Gas Tank has 2 Fuel lines 1 large one about 3/4 inch to feed the Pump by gravity flow with Gas out of the tank / and one going into the tank for Fuel return ...
Link to Video

https://www.google.com/search?client=firefox-b-1-d&q=1970+Mercedes+280+SE+how+do+you+hook+up+the+rear+Fuel+Lines+correctly+%3F#fpstate=ive&vld=cid:d4886566,vid:WNRFZ5hBfq8

All of this is important for several reasons :

Example >(1) if you block off the return Line ( don't do this I discovered )
The Low Pressure Pump will get very Hot as the Gas going through it keeps it cool " at the right Pressure "
THIS HOT PUMP syndrome will happen in just a few Min's pump running ( about 5 Min's > pressure will build and perhaps Blow seals
and damage the Injector Pump and I am not sure what all > you need the return line and you need it hooked up right no doubt

(2) the Fuel I suspect from the Fuel return Line has increased pressure as it I think passed the Injector Pump ( not sure on that ? )
( I used a Clear Plastic Gas line to get the Car running with a Temporary Gas Tank at rear of Car and noted a LOT OF FUEL go's through the Fuel Return line not a small amount at all a lot ! .

So again whats the right way ? to hook the return line to the Pump ?
or to as I have seen leave that port blocked and hook it to the pressure line going to the motor and the Tank ? >

I Can not find any real Info on this ?

in fact for these W 108 Gas Fuel injected car's the 280 SE are simple left out of several manuals I have ?? they just leave these Cars out of the manuals for some reason > Yes I am sure you can but them somewhere etc but I all ready have several Mercedes Manuals but none of them cover This Car ? They cover all the others cars the same year but not the 280 SE 6 Cylinders ? They skip that one.

Wow these Pumps are Costly I am glad I grabbed 3 of them / The Motor Run's great BTW I guess I well Part out the rest.

Thanks if anyone has the correct info Lets keep these W 108 W109 W111 going

[aluminum]

Originally Posted by subforry

I was just under my w108 280SEL. The return fitting at the pump runs up to a T in the return line. The other connectors on the T run forward to engine and backward to the tank.

Thanks : SEL Most likely a V8 / ( mine is a280SE 6 Cylinder 1972 with MFI )

But anyway your Return line hooked up to the return port on the pump

Both I looked at have that port blocked off (with a screw the port is " threaded" and you can block it )
And the return line hooked up to (1) The Tank return port on the tank (2) the Pressure line to the Motor ? (3) The return Line itself
*** ( But Not to the Return port on the Pump ? ) *** I am hoping someone can enplane that to me ?

As 2 of those lines are under pressure , Different pressure I think seems strange > To return pressure to the Tank makes sense
to keep pressure from building to Excess at the Injection Pump , Injectors etc .

Very strange set up ? the return line is under fuel pressure when key is on
as Fuel Pump is always running ( Key On ) and they hook it to a Line going to the motor that also under pressure ?
On top of that the pressure is also going back to the Tank ?

This is hard to digest LOL ???
( if you watched the Video it seems to show the same Return line hooked to Pump Port and a T connection )