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hangfire 03-30-2006 03:43 AM

fuel-return line
On a diesel engine..can a fuel-return line be plumbed into the fuel-fill hose? If so, how[?]

Gord May 03-30-2006 05:17 PM

I can’t think of any reason the Diesel Fuel Return line couldn’t be plumbed into the Fuel Fill line, EXCEPT the considerable practicality of obtaining a suitable fitting.

The minimum size of a Fuel Fill is 1-1/4" diameter, whereas the Return Line may be less than 3/4" (smaller, depending upon engine).

I’d recommend a reducing ‘Y’ fitting, 1-1/4" min at left upper stem & lower common stem, and sized to suit return line at upper right stem.

I have no idea where/if you could source one.

The fuel tank is probably not intended for Diesel, if it does not have a Return Line fitting.



Bedouin 03-30-2006 05:29 PM

There is no reason that you can not place the fuel return line into a fuel filler hose but I have to agree with Gord about fittings. It is normal practice to fit the fuel return to the fuel tank which is an easy exercise but you didn't give a reason that you couldn't do it that way. The only place you can't fit the fuel return is to the line from the fuel tank to the motor(fuel supply) because if you ever get air into the system by running out of fuel for example then it will not be possible to bleed the air out by pumping it through the system. It would also be difficult if not impossible to bleed air out through the bleed screws.



Gord May 03-31-2006 06:14 PM

BTW: The Fuel must ALWAYS return to the tank from whence it came.

Gallivanters 04-03-2006 11:32 PM

I'm certainly no expert, but...

How about adding a "T Fitting" to the fuel tank vent line, which is often the same size as the fuel supply line.


Gord May 04-04-2006 06:52 PM

I’d be careful in tapping into the tank vent line.

“Wet Vents” (wherein the Vent is also used as a drain) work in conventional plumbing systems, because the vent pipe is much larger than the drainage that occasionally enters it, still allowing air to pass through the vent.

A fuel return line, sized about the same as the tank vent line, might fill the vent (/w fuel), thus preventing air from entering the tank. This could cause a partial vacuum in the tank, staving the fuel pump & engine.


Gord May

Gallivanters 04-04-2006 11:34 PM

Okay Okay....

I'm certainly not an expert, but,

what do you think of this as another simple method for installing a diesel fuel return line...

Remove the inspection plate from the top of tank and install a proper fitting on the plate and re-install.

And be sure to use the right sealant on fuel tank fittings. I used a silicone-based sealant to bed an inspection plate on the aluminum diesel tank I'd installed in our last boat. The sealant turned to a slimy gooo within a few weeks. And I immagine a few gobbs found their way into the fuel, which could have wrecked havoc on the fuel pump & injectors, were it not for our Racor.

I'm also told that it's important to keep the hot return fuel away from the fuel pick-up point, to prevent heat build-up, I suppose.

While on the subject of fuel systems... the first time I put fuel in our last boat - the bilge pump immediately sprang to life and created a big problem, which required a big clean-up effort and surgical removal of the tank. Not an Easy Job. I found holes in the bottom large enough to put my finger through! I replaced the tank with a new one in Hawaii - at great expense. The new tank required later removal in Australia and Guam during the next five years because of pin-hole leaks which kept spring in the bottom. Corrosion problems persisted until I replaced the bonding wire. The next five years were leak-free. The core problem was solved with three bucks' worth of wire & two terminals.

Our new boat came with Stainless Steel tanks and the fuel hoses were sticky & nasty. It cost over a hundred dollars in materials to replace ALL hoses & clamps with "da kine". I also installed a good electric fuel pump and mounted the switch where I can reach the bleed screws, Racor and switch from one location. And I painted the bleed screws yellow while I was at it. Maybe I'm being a bit anal, but now I completely understand my entire fuel system and hopefully, will never have to think about it ever again.

I'm sure there's a value for Peace of Mind... especially on a dark night at sea.


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