looping the return on a single tank system?
 

Hi I have a 1978 Mercedes 240D. I have been pretty succesful running it on waste vegetable oil. I keep hearing about looping the return so the hot fuel doesn't go back to the tank. I really want to do this on my mercedes but have no idea on how to!!!!. Can anybody please provide me with a diagram, and explain to me how this is done on a 78 mercedes 240D single tank system. It would be greatly appreciated.

Banjo bolt.
 

Look for the injector bypass hose running from the number one injector to a banjo fitting on top of the secondary fuel filter assembly. Remove the bolt which secures the fitting and replace it with a standard bolt - i.e. not hollow with hole punched in the side. I think this'll do the trick.

Jay.

P.S. Forgive my ignorance, but why do you wish to stop the return flow?

Since VO has to be heated up quite a bit and most people don't install an in-tank heater, they'd rather not lose all that freshly heated oil back to the tank and instead keep it circulating in the engine compartment.

If you just close off the banjo fitting, you'd build up some crazy pressures in your injector lines and likely blow a return line hose in no time.

Seems like a better idea would be to install a y-fitting on the incoming fuel line (from the tank, before the fuel pump) and then loop the return line (cigar line) into this new y-fitting.

Not sure how well that would work or what damage that may cause to the fuel pump, those pressures coming back through the cigar line can be crazy at times.

Is there anyway you could post some pics to help me better understand?

I just sold my W123 and have never run VO before, so let's let those with wisdom chime in...any minute now...

Just ...
 

take the cigar hose off,
put a manual swithing valve if possible or have tools handy to restore orig config in case run out of gas ,
send fuel return back to the hose going to inlet of fuel filter. use barbed t here.

you should block off banjo bolt on top of filter however you still need all those fuel lines connected. so easiest thing is to have the banjo bolt welded on bottom so fuel flows out to return to tank but not in to filter

the reason you should block off banjo is beause you will create suction there which wuii suck fuel from wrong side of filter potentially feeding engine unfiltered fuel. i got this tip from bgkast

good luck.

I never rerouted the fuel lines on my 300SD that burned WVO. I do add 10-20% RUG to thin it out. Works great as long as ambient temps are 45 F or higher.