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Fuel return line Question

pigpen60

Registered
Does the fuel return line need to be a seperate line back to the tank or can it be "t'd" back into the fuel feed? Beau coup years ago I was told to not fill the fuel tank on a dump truck over the return line fitting Cause it can cause a runaway. Ive always thought it would be alright to "t" back into the feed on the suction side of the lift pump. What say you?
 

kwfiggatt

Registered
I tee'd the return back into the suction line on a Listeroid and kept getting air in the pump. I then changed the plumbing to dump the return back into the tank and haven't had any problems since then.

I think I read here that putting the return line back into the pump inlet is a no-no, which is why I changed it, along with the aggravation of having to bleed the pump by flashlight on cold nights when the power was out (listeroid drove my backup genny).

If you think about it, any combustion gas that leaks into the injector is going to come out of the return, which is probably the reason not to plumb it back into the injection pump inlet.
 

Oil Power

Registered
I would not advise teeing the injector return into the fuel feed line. Even a small back pressure in the injectors is most undesirable. While no air should come from the injector leak off, it would be difficult to bleed the return side of the injectors of air. Pockets of trapped air could therefore work there way through at any time causing trouble.
Hugh
 

brianh

Registered
Yes, one of the most, if not the most important functions of having a fuel return in a fuel system is to be able to rid the system of air. If you tee the return back into the supply line the air just gets recirculated. Take it back all the way to the tank.
 

miltruck

Registered
All of the above plus on some engines the return line is warmer than the fuel supply. If attached to the supply side the fuel may overheat. Older Cummins and 2 cycle Detroit's actually get quite warm.
 

Toesmack

Subscriber
Last Subscription Date
02/08/2019
Yes, you need a separate return line. When running the return back to the tank for all the reasons noted by everyone here, make sure end of the return tube is run all the way to the bottom of the tank so it stays below fuel level. Otherwise prime can be lost by bleed off of the return system allowing air into the backside of the system. I have seen this in both John Deere and Perkins engines, possibly some others, who can remember?

As to combustion gasses entering the system thru the injectors, if that happens your problems are much larger that air in the system. Old school nozzles maintain about 1800psi to 2200psi until the pump send a small charge to the injector causing a spike, which will cause the injector to "pop off"
 

cornbinder89

Registered
Yes, you need a separate return line. When running the return back to the tank for all the reasons noted by everyone here, make sure end of the return tube is run all the way to the bottom of the tank so it stays below fuel level.
"
This is not a hard and fast rule, it depends on the fuel system. It would be recommended on a fuel system like Detroit used on their 2 strokes. None of my others have it to the bottom of the tank.
Both Cummins and Cat powered just dump into the top of the tank and have no problem with drain-back.
The Detroit system uses a simple gear pump and a restricted fitting, so any air would allow the fuel to syphon back over time.
In all cases a seperate return is required, just that it doesn't have to be below fuel level on most systems.
 

OTTO-Sawyer

Subscriber
Age
57
Last Subscription Date
07/15/2019
Obviously the return line would have to larger than the feed line .
Not So ^ , and No Reason Why it would need to be.

The Fuel Pump only pumps fuel on the down-stroke of the pump (or half the time) while the return line is Continuous Flow IF/When There is Excess Fuel to return.

My 4hp Stover T has the same size in as out, as does my New-Way.

I'd have to do some digging to find pictures of my other engines, or do some digging out in the shed to get new pictures of them, but the 6hp Fairbanks Morse Engine on my 1/2 Scale OTTO tractor also has the same size feed & return lines.

IF you're running over and slobbering gas all over the place it's because your stand-pipe is set too high.

:salute:
 

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OTTO-Sawyer

Subscriber
Age
57
Last Subscription Date
07/15/2019
And Right AFTER I posted That I realized the OP was referring to a Dump Truck and NOT Hit & Miss Engines. . . :headbang::headbang:

So. . . in spite of my original reply not being in line with the original question, I would still say the Return line does NOT need to be larger than the feed line, as most old cars I ever worked had say a 3/8ths feed line and a Smaller 1/4 inch return line.

:shrug:
 

cornbinder89

Registered
And Right AFTER I posted That I realized the OP was referring to a Dump Truck and NOT Hit & Miss Engines. . . :headbang::headbang:

So. . . in spite of my original reply not being in line with the original question, I would still say the Return line does NOT need to be larger than the feed line, as most old cars I ever worked had say a 3/8ths feed line and a Smaller 1/4 inch return line.

:shrug:
Cat mechanical 3406 uses -4 return line, -10 feed, Cummins Big cam uses -10 for feed -8 for return, so no it doesn't have to be bigger. I'd have to look on my 6-71's but I think they my be -6 or -8 with -10 on the draw side.
Kubota uses much smaller return, along the line of the Cat,but everything is smaller.
Leyland 680's used 3/8" both supply and return IIRC, Gardner 6LXB May have used 1/2" supply with 3/8 return IIRC Going back 30 or more years on my memory here
 

Beanscoot

Registered
I would agree the return line need not be larger than the supply line, except for those engines that have more fuel coming back than going out.
:bonk:
 
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