Fuel line routing and banjo bolt help requested for two tank system - PeachParts Mercedes-Benz Forum

Jimmy Joe · #1 05-09-2004, 12:32 AM

I hope one of you talented MBZ mechanics have some thoughts on this. I am installing a second tank (veggy oil), and am perplexed at how to address the fuel filter banjo bolt issue. If I put a solid bolt to avoid veggy oil from being returned to the main tank, do I end up blocking the injector return line?
Where is the best place to put the fuel tank selector valve?
Surely I can find that one soul out there who can provide pics or answers to my dilemna.

Thank you.

p.s. I have been all over the infopop board, and greasel's and greasecars sites. No luck for my particular issues.

She's an ole 1980 300 diesel, California Dreamin

coachgeo · #2 05-09-2004, 12:49 AM

Your answers are all where you looked. It's just not easly spelled out in one thread. You just have to read, draw your plan, read more. redraw etc. till you have what YOU want. There is no ONE reasonably costing solution. There are many.

IMHO the IDEAL route to take is, make sure you have excellent heating of the incoming fuel as close to the IP as you can get it. If you have this you DO NOT need a return loop. You see as far as I can tell the ONLY reason people use a fuel return loop is because the unused vegoil coming out of the IP and injectors aids in heating the incoming oil being sent to the injectors. Ifffff you take the time to make an excellent heating system prior to the IP for the veg. oil then you dont need to return loop. Just put in a 3way valve somewhere in the system that switches return to vege tank or return to fuel tank. This requires running both a return and incoming fuel lines to your tanks.

The advantage to this IDEAL way is now your not fawking as much with the concepts designed into the 617 engine's fuel system.

coachgeo · #3 05-09-2004, 01:58 AM

Scary things happen when I think LOL

Look HERE for an idea on how to still get use of the hot return fuel but NOT use the typical fuel return loop to do so. This may be very usefull to avoid the issues with fuel return loops and the air bleed design of the MB fuel filter arrangement. (Banjo bolt bleeder)

Jimmy Joe · #4 05-09-2004, 02:15 AM

Coachgeo,
One problem that I have read about is the venturi effect when using a single return without modifying the banjo bolt.
You are, however, recommending a return to the veg tank, but I have read that the return loop not only aids in heating, it also greatly reduces the vacuum in the system.
And then there is the issue of switching over and sending all the diesel in the IP to your veggy oil tank.

It seems like a compromise any way you go, and I am fishing recommendation. Also, I can't find a clear understanding of how to merge the IP and injector returns...

coachgeo · #5 05-09-2004, 02:34 AM

Quote:

Originally posted by Jimmy Joe
Coachgeo,
.. I have read that the return loop not only aids in heating, it also greatly reduces the vacuum in the system. ...

It seems like a compromise any way you go, ...Also, I can't find a clear understanding of how to merge the IP and injector returns...

Good point on the vaccum. I was thinking 12v fuel pump back by the veg. tank pushing fuel though which also reduces vaccum issues.

"Merging the IP and injector lines"... what a nightmare!!! Been there done that and it didn't work worth shiat. If I was to go that route again on an MB I would NOT merge them. I would go the common route of welding/puting expoxy in the bleed hole at the bottom of the banjo bolt. Then you start to loop your return fuel line "after" the banjo bolt atop the filter "T" into the incoming fuel line just before the pre fuel filter.

I say before the pre filter cause....Since the epoxy fubared the MB engineer's air bleed system then maybe the more recently discussed use of a gasser car air bleeding type prefilter would help bleed some air out? Replace the MB prefilter with the airbleed type from a gasser. These were designed for those gasser cars that had vapor lock issues. Plumb the bleed port line from this prefilter to the return line to the diesel tank. The tiny amount of vegoil/air that makes way down the fuel line into the diesel tank won't make much difference unless your in alaska?

Jimmy Joe · #6 05-09-2004, 03:01 AM

It is interesting how you differentiate plugging the 'bottom' of the banjo bolt, instead of just replacing it with a solid bolt.
This makes me think my earlier concern of the return from the injector just being dead ended doesn't happen in your scenario.
Am I correct here?
Everything else makes good sense except that damn octopus of hoses from/to IP and filter, and where to put the new lines.
I really think I am gonna have to see it to fully 'get' it.

P.E.Haiges · #7 05-09-2004, 10:51 AM

Did anyone ever think of using a fuel switch valve like the dual tank pickups have? Using this type of valve, what came from a WVO tank would return to the WVO tank and same for the Diesel fuel tank.

That way you wouldn't have to modify the original MB plumbing around the IP. I don't know what this valve would cost but you might be able to find one in a junk yard.

P E H

coachgeo · #8 05-09-2004, 12:07 PM

Jimmy, Filling the air bleed hole in the "bottom" of the banjo bolt means your Octapus hoses stay in the OEM configuration. You dont fill the top of the bolt. You only fill/block the air bleed path in the bottom of the bolt. AFTER the banjo bolt you "T" your return. In this configuration the banjo bolt just becomes a way to tie the octapus return lines together and feed them into single line. In OEM configuration it does the same thing but it ALSO acts as an bleed for the fuel filter below it.

PE Haiges, Two tank fuel switch valves ( Polick (sp?) values about 60 bucks new) are used often. Other things have to happen to use them though. They alone do not address the discussion hear. On the MB return system (as well as many other diesel engines) "air" and "fuel" is feed into the return line hose on its way to the tank. If you use a "T" or valve to loop this return back into the IP you get air problems.

For those not understanding why to loop in the first place: The returnline fuel helps heat up the thicker vegetable oil and thin it out to the consistency of diesel. This needs to be done or you get incomplete combustion, thus coking of the injectors and ring lands etc.

P.E.Haiges · #9 05-09-2004, 02:22 PM

Coach,

But by using the 2 tank switch valves, any air and all hot fuel would be returned to the tank it came from. Thus Diesel would be returned the Diesel tank and WVO to the WTO tank which ever one was switched to.

The reason its done on Diesel pick up trucks is so the return fuel from tank #1 doesn't overflow tank #2, it goes back to tank #1 that it came from. Thus the fuel level in tank #2 remains constant until it is switched into the systrem and then the return fuel goes back into tank #2.

P E H

coachgeo · #10 05-09-2004, 03:45 PM

Quote:

Originally posted by P.E.Haiges
Coach,

But by using the 2 tank switch valves, any air and all hot fuel would be returned to the tank it came from....
P E H

Oh ok.... I got your meaning. I was reading your suggestion from the vege world ballpark, but you were speaking from the normal worlds ballpark LOL. . Actually I see now we are in the same ballpark "almost". In the vege world ball park folk do have two tanks (one tank is diesel and the other vege fuel). *Some use two switch over valves like the normal world ballpark(one switches tanks.. other switches path of returning fuel) but not in the way you describe it.

Those in the vege ballpark; when running on vege oil, want to tap into that hot return vege oil to reduce the viscosity of the incoming vege oil. To tap into the heat source from the returning vege fuel, those in this park use the switch over valve on the return fuel side to send hot return vege fuel in a loop back to the IP. Unfortunately often this loops air back into the IP as well. Some install bleed valves, others for a quick couple seconds will return vege fuel to the diesel tank to purge air from the system. When running on diesel they switch the return fuel path back to the diesel tank.

What you suggest though is actually, what I am theorizing might be a better way to go. Only difference between us is I'm adding a heat exchanger to tap into the return fuel's heat source. Like the vege fuel return loop, a heat exchanger would heat the incoming vege fuel and help reduce viscocity, but unlike the fuel return loop this heat exchange would happen without the air issues.

*Most do NOT use a return line switch over. They have both diesel and vege fuel return line feed into the IP in a loop. Some of these folks have air problems, some don't.

clarknova · #11 05-09-2004, 06:51 PM

still trying to wrap my brain aroung the plumbing of a WVO dual tank system.
do any of y'all have a good diagram that explains how to plumb this?
it seems like two solenoid switches are necessary, one for feed and one for return, but that still seems like a fair amount of fuel would be transferred to the opposite tank upon switching.
still new to MBs and even newer to the WVO world...

westkill · #12 05-09-2004, 07:27 PM

http://biodiesel.infopop.cc/eve/ubb.x?a=tpc&s=447609751&f=159605551&m=740601947&ORIGINAL_REFERRER_URL=http%3A%2F%2Fbiodiesel.infopop.cc%2Feve%2Fubb.x%3Fa%3Dtpc%26s%3D447609751%26f% 3D159605551%26m%3D740601947

try this

pdxwaker · #13 05-09-2004, 09:32 PM

From what I've read there is no 'ideal' way to plumb your system. In addition to the items already mentioned keep these in mind:
- using individual returns to the veg/diesel tanks (i.e. 6 port valve) will cause some mixing of fuels at switchover (important if you are relying on your veg filter for wvo)
- a looped return can be setup to 'backflush' your veg filter with diesel. To do this use 2 3 port valves... you'll have a looped return when on veg & a return to tank when on diesel. If you delay switching the return/loop valve after switching the source fuel valve you'll essentially loop deisel for a short while backflushing diesel fuel into your veg filter. This has a couple of advantages... it can clear some of the filter element and it also eases the switchover to veg since your filter isn't filled with thick veg oil at switchover.

-John

coachgeo · #14 05-09-2004, 10:03 PM

Quote:

Originally posted by pdxwaker
...
- a looped return can be setup to 'backflush' your veg filter with diesel. ...
-John

If you use a "shared" fuel filter (same filter for both vege and diesel) you wont have to backflush if you follow the common procedure of switching back to diesel before shutting down.

pdxwaker · #15 05-09-2004, 10:38 PM

Quote:

Originally posted by coachgeo
If you use a "shared" fuel filter (same filter for both vege and diesel) you wont have to backflush if you follow the common procedure of switching back to diesel before shutting down.

That's true... I guess I'm too paranoid about my injection pump to use the stock filter w/veg oil. What micron level is the stock filter rated to? I also prefer to have a water separating filter (for veg oil) due to the possibility of water content in WVO...

-John