Looping the fuel return - engine won't run

[warp.routine]

89 (i think) 1.6L n/a vw diesel

I am "converting" to biodiesel (meaning that I am adding a vegtherm and viton lines).

I tried to set up my vegtherm with a looped return line, t-ing the fuel return back into the fuel feed line. This caused my motor not to run (it would start, chug for a few seconds, and die... as though it couldn't suck in any fuel).

It did this on straight diesel, so I know it is not a viscosity issue. It also worked perfectly (and still does) when I route the return line back to the tank.

Is there some kind of pressure lock that occurs when looping the return? Or could it be an air pocket in the line? How can this be resolved? Does the injection pump have a purge fitting, or is it auto-purging only?

Thank you a million time over for any hints, answers, or advice you can give me!!!

[745 turbogreasel]

Maybe your vag therm is clogged?  Or leaks a lot like the last one I saw.
When looping the return, you totally eliminate all air purging functionality....real bad if you need to prime.

Try this; pull the return side off the fuel inlet T, cover the inlet leg, crank the engine till fuel overflows the veg therm, then plug it all in with the least spillage possible.    I am guessing you may have choked on air in the line.

I ran mine like so:
fuel line== T fuel line fuel line fuel line Pump
               H                                   Pump
               H                                   Pump
               H                                   Pump
XPurge line T return line X return line  Pump

T= T fitting
X= manual ball valve
so i can shut the return line, and open the purge line(hose into a fuel bottle)

[rabbitman]

When looping the return, you totally eliminate all air purging functionality....real bad if you need to prime.

I think that's the problem.

[the caveman]

First of all, are you converting to run on WVO or biodiesel?. Biodiesel doesn't need [or at least shouldn't need ] a vegetherm. Biodiesel is vegetable based diesel fuel.
Anyways, having converted over 30 vehicles to run on WVO ,i have never had much luck looping the return line.
I wasted more time trying to get an engine run doing that then just the regular return setup.Not to say it doesn't work, but purging out air when it's looped is very fustrating. IF you must use a loop, purge the air out by leaving it disconnected until the air is gone, then re-attach it all and then try. I would think that if you are heating everything properly you shouldn't need the loop anyways. I run almost all winter without it with zero troubles.

[745 turbogreasel]

Anyways, having converted over 30 vehicles to run on WVO ,i have never had much luck looping the return line.
I wasted more time trying to get an engine run doing that then just the regular return setup.

Any idea why?

A properly running diesel fuel system ingests 0 air.

All diesels really do have a looped return, just most of em just have an extra 10 feet of hose so the loop goes back to the tank.

Long term wear issues, and initial purging aside, how could it possibly make any difference?  I did a fair number of looped return conversions on Dodge, Ford, MBZ, Volvo, and VW  vehicles, and never had any problem with this aspect.

You should have some clear line in your return, so you can see how much air is in there.

[rabbitman]

A properly running diesel fuel system ingests 0 air.

All diesels really do have a looped return, just most of em just have an extra 10 feet of hose so the loop goes back to the tank.

A "looped return" to the tank will still get the air out since the air will end up in the tank and the tank is vented to outside, while a true looped return without going to the tank won't give air in the system anywhere to go.

[745 turbogreasel]

There shouldn't be air in the system.
If a small amount gets in, it will go through the injectors.
After that, why would it have any trouble running?

[the caveman]

It's not that it won't work, but depending on how the lines run , it can be an issue. For example the 3 GM's i've done would just not run set up like that. Spent many frustrating hours trying to sort them out. It's just that after doing a few,[ not just GM's ] the only times i had big swearing attacks was when i tried looping. This includes IDI Eurovans, TDI jettas etc,etc. They all ran perfect- well better actually, without the loop. Again i'm not saying it won't work, and yes there shouldn't be any air to be trapped, but depending how the other lines are run , quality of components and fittings etc, some installations will not run any where as well as without. BTW why should a converted system run any different from how  90 % of small diesel fuel systems are.
Again, the only reason to loop is to keep heat at the IP end of the lines. If the vehicle has a proper set up with heat at the tank, filter, lines and at the IP there is no need for it.

[fatmobile]

Caveman, If you had a vacuum gauge on any of the fuel lines you would not have run the return all the way back to the tank. I works the pump 4 times as hard.
 I don't think he got all the air out of the loop before conecting the lines and trapping it in the loop.
 Like mentioned; you need a clear section in the loop to see if there is trapped air.

[warp.routine]

First of all, are you converting to run on WVO or biodiesel?. Biodiesel doesn't need [or at least shouldn't need ] a vegetherm. Biodiesel is vegetable based diesel fuel.

I am running 100% bio, which is twice as think as diesel. Pre-heating the fuel helps with atomization (as I am sure you know quite well). I don't think I 'need' the vegtherm, as the bio is a whole fluid whereas WVO can separate and solidify, but it will defiantly help the fuel flow on the colder Vermont days. I still haven't decided on if or what I will do for tank heating.


Also, the ball valve is a great idea to purge the lines of air before closing off the loop.

Lastly, the reason to loop the return under the hood instead of through the tank is to keep the return fuel (which is already heated) going back through the vegtherm. This allows the fuel to remain at optimum temp with less amperage draw from the term.

[theman53]

http://www.fattywagons.com/fwproducts.htm

These guys have some stuff that will heat your fuel. Line and filter heating stuff looks real cool.