return line... which one?

running a return line... what is the best way?

I know the full return line is the best, but gotta ask about my cousins design... he's say'n to T into the feed line and let the return fuel go right back to the pump...

what do you guy's think? if the T works I would have less fuel line to make up, but if not, then I'll have to go my original idea...

One advantage to returning the fuel back to the tank is that it would have a cooling affect and remixing with fuel in tank might also remove some air. Most factory EFI type tanks do it that way, if it would matter much compared to bringing it back to the pump I don't know.

In all applications I have seen the return line runs back to the fuel tank.

i think the reason why the return line would go back to the tank is because the returning fule would go against the gravity feed effect of the tank to pump line

Returning the fuel to the tank also keeps it cooler.

MPGmustang":fijf0y1b said:

. he's say'n to T into the feed line and let the return fuel go right back to the pump...

Click to expand...

Run it back to the tank. It's easy enough to run a return line to the filler neck.

The pump should be near the tank anyway. If you have it in the engine compartment, the pump won't work as well and will also run warmer.

All automotive EFI applications that I am aware of return fuel to tank. The main reason is fuel cooling, as fuel in the rails can get quite hot under some circumstances. Fuel temperature affects fuel density, which affects A/F mix. The other reason is to provide a constant purge of any fuel vapors that may occur in the system. Vapor in the fuel rails can cause all kinds of grief.

Some OEM marine EFI systems do not return to tank but rather to a proprietary (and expensive) fuel cooler which is part of the fuel delivery system. I suspect that one of the reasons for this is to allow these engines to be retrofitted into boats with no provision in the tanks for a return line.

I have done both. The best way is to use a return line.

Here is a pic of my old setup using a "T" and a Mopar fuel filter.


Here is a link to my electric fuel pump install showing the return line.
viewtopic.php?f=1&t=58360&p=447735#p447735

I didn't want to weld a bung in my fuel filler neck at the time. So, I used a Ron Morris sender that had a return built in.
My stock fuel line is being used as the return line and the AN is the supply line.

Finally, I was over a friends hose one day with a welder so welded a bung to the neck. Never used it.
What year do you have again? Its yours if you want it.

that ron morris would be really nice... I'm still deciding which route I want to go... but for the price of that sending unit.... I really don't know how old my current unit is. I do the PO replaced the tank but IDK about the senting unit. maybe it's time... hmm decisions...

Does 10's method. It works.

well I'm going the ron morris route, my dad and I both like the idea of the gas lines outside of the trunk.

We are also argueing about a return line, I mentioned a steel braided line but he likes the idea of a hard line to feed.

I believe the elec pump is not that big on pressure, maybe 30psi max IIRC, so would a simple 3/8 alum hard line zip tied to the current line and rubber hoses and clamps be strong enough? I can get 25ft of alum 3/8 line for $35 and then go to local stores for rubber hoses and hose clamps.

I don't want to use those $AN$ fittings so hose clamps are good enough for me... this isn't a 'shiny car' but a usable car. what do you all think, will it be adequite for my application?

Why not just use some steel line should be lower cost than Aluminum?

actually a spool of 25ft alum line is only $35, locally all steel lines come in individual lengths and combined are more $$$...
http://www.mustangsplus.com/xcart/Natur ... -Line.html
using the hard line as often as I can I'll connect peices with rubber line.

then get this sending unit
http://www.mustangsplus.com/xcart/1965- ... -Unit.html

then my fuel system should be ready...

What I have going so far is this....

Where my Z-Bar was bolted I made a plate with two pipe unions/couplers on it. one side will have a -8 fitting (what I setup my rails to take as it was easiest) and the other will have a -6 fitting (both steel hydraulic fittings as they are cheap) I will do something similar at the rear but will most likely use a 3/8" union (the -8 fittings fit the rail best and will be as big as I ever will need on E-85 if I go that route) inbetween this hard point will be just some SS hardline (AL is cheaper though) flared with tube sleeves and nuts. the flex sections are pushlok hose. WAY easier to assemble (I will never go back unless required for tech).

I will be returning to the tank (my fairlane tank mounts from the bottom so no in trunk hoses other than the filler)

I will be using a "frame" mounted bosch pump (on a plate mounted on bushings to help keep noise down) return will be to a tube with a -6 fitting on the end (to make sure fuel is mostly deposited at the floor of the tank instead of spraying it all over inside the tank)

I had looked at this setup but my tank is barely deep enough for it
http://www.tanksinc.com/index.cfm/page/ ... /prd84.htm
I would have also have to notch my trunk floor with a step and would have to drop the tank to access the wiring or fittings on it.

I will be working with a NEW tank and sender so no welding issues.

you might be able to just drill a hole in the tank near the sender and install a bulk head fitting like is used on a fuel cell (with a sealing o-ring) I am not a fan of returning a filler neck on a rear fill tank.....lots of extra fuel hose to run and in a unprotected area.

I am going with the AN fittings since I HATE having to cut hose off barbs that has turned hard and then you are stuck cutting a new piece of hose to length everytime you take something apart.

one option might be to get hose crimped at a napa but it might be just as cheap to use the pushlok hose. try to lay it all out to use as many straight fittings as possible since they are half the price (around $8 for -6)

yeah I won't be putting any gas lines inside the trunk... I got a new sender unit that has a 3/8 send line and a 5/16 return ports, figure this will be safer. for the alum, I have a flare tool, not a double flare, but after one flare I'll use some fuel injector hose with 2 clamps on each end after the flare. this should keep it on. I'm going to mount the pump on a self made mounting plate like ron morris, with some added 'rubber' to help 'cussion' the vibes. hopefully a 30psi is the highest I'll ever see.

fragola hose runs $3 per foot and -6 straight ends are $4 each from summit.

So 8 hose ends and 3' of hose would only run you about $35. you would need some money for the adaptor fittings though. If the TBI unit uses saginaw style fittings you can get steel ones from places like Speedway motors for only a couple bucks a piece.

what pump are you running? another option to look at is maybe using OEM style nylong fuel line and quick disconnects. this might let you plug directly into the TBI unit with no adaptors and the same for the fuel filter.

don't forget that AN flares are 37 degree and not 45 degree like most flaring tools are. if you are flaring for AN you will need a tube sleeve and nut.

See if you can find a shop with a hydraulic tubing tool (I am planning on buying one when I plumb all my hardline) they can flare saginaw style ends (you will need to supply the nuts and o-rings though), AN, and inverted flares. They can also get dies for doing OEM style quick disconnect fuel lines. These flaring tools and a full set of dies are about $400 though (will do up to 1/2" tubing though) as I said if you can find a local shop with them you could take your tubing there to be flared as needed.


A nice way to do this woudl be to have a saginaw flare on one end of a tube and AN on the other, route it down to where your frame line will be and use some bulkhead fittings on the bellhousing to hold the hardline and let you make the change to a flex line with a rigid point. then do the same on the frame.


My S10 has a hardline down to the transmission and then just a nylon flex line to the frame (it is slid up over the hardline on the motor side....frame side is a disconnect)

Try to polarize your fittings....make one longer than the other where they attach so you don't get them mixed up....or use different sizes like the factory does....maybe different colored AN fittings...or even a band of colored tape or zip ties to allow identification.

won't be using any kind of connectors... just hoses clamps and 3/8 alum line.

call me cheap, but I figure the old line will be return line
my new 25ft of 3/8 line will be the send line
no special flaring, just like brake line flares I'll flare the tip so the rubber line won't slip off with the clamp on.
the pump looks generic, IDK... I'll post pics when done with the system.

I'm not doing an fittings, just hose clamps, flare the end of the hard line where it converts from hard to rubber.

the rubber is fuel injection line, rated for 60 psi, I'm running no more than 30 psi if that.