Fuel pump return line

airbrushguy

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I am in the process of putting a 500 Cadillac engine into my 49 Hudson. I am using the original type fuel pump and it has a return line that I assume went to the gas tank. What effect will there be if any,It’s five block off and don’t use this return line.
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airbrushguy

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BTW...the engine will have a Holley carburetor...
 

Darius

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Airbrushguy,

Its likely there wouldn't be any effect for blocking that return line, The original engine and fuel system it was designed to benefit are no longer in service.

However, why wouldn't you choose to have a return line? Assuming the original isn't clogged with little critters, or bent, and that it is securely connects to a "good" fuel tank, there could be benefits to a return line.

Just sayin,

bro. d
 
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48Austin

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Good things; Less likely to vapor lock, more fuel volume. No down side.
 

airbrushguy

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Just trying to cut down on unnecessary plumbing, will certainly install if needed.
 

airbrushguy

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Is it a steel line on the original ‘76 Cadillac, and what diameter should it be?
 

5one9

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If you have to replace the line then I wouldn’t do it. IF it has a vapor lock issue (it likely won’t) then you can go through the effort of adding it.
 

airbrushguy

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I ask because Hudson did not have a return line.
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airbrushguy

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"its likely there wouldn't be any effect for blocking that return line, The original engine and fuel system it was designed to benefit are no longer in service.

However, why wouldn't you choose to have a return line? Assuming the original isn't clogged with little critters, or bent, and that it is securely connects to a "good" fuel tank, there could be benefits to a return line.

Just sayin,

bro. d"

Actually the original engine and fuel system is still in service, except it is in a different car body.
Did the return line run from the fuel pump all the way back to the tank/ filler neck?
 

Darius

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Okay, I confess to being somewhat confused, a condition that is happening more all the time. :confused:

I had thought you were saying that the Hudson had an original fuel return line and were wondering if blocking that line off would cause a problem.
If I'm correct (NOW), you were saying that the original Cadillac fuel pump is one with a port to feed a return line; and have further confirmed that the Hudson body has no existing return line.

Assuming I've got it right this time, the answer basically stays the same, in that it's your call. That said, depending on access in the Hudson and relative ease of installing, I would go with the return line.
That is a decision based on my own experiences at the higher altitudes of Utah as well as the hot summers. Both of those physical conditions increase the possibility of vapor lock issues.

Here are two links which show you can go either way:



To answer your question, yes, the return line goes back to either the fill neck or to the tank.

Hope that helps,

bro. d
 

Cadillac Kid 1

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Okay, another confused duffer gets into the act. The bypass on the pump serves two purposes on the Cadillac engine. First of all it returns fuel that the engine isnt using and secondly it keeps fuel and vapor moving to elminate vapor lock. Without the bypass there is an EXCELLENT chance that you will over pressure your carb and in warm weather vapor lock. You haven't mentioned the "state of tune" of the 500 but anything over bone stock needs all the fuel pump capacity that a stock fuel pump will deliver, and blocking off the return will not help.
Suggest you run a 5/16 or 3/8 line back to the tank.
To cure my vapor locking (due to a hot engine compartment) under low fuel flow where the 1/2" fuel line was exposed to engine heat I went to a bypass regulator with a full size (1/2" ((or 8 AN for you purists)) return line. No more vapor lock.
Greg Surfas
 

airbrushguy

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Thanks for clearing that up fellas.
However, after reading your posts this morning, I went out to install my return line and what did I see?0.jpeg
The return line fitting is plugged.
Is this normal, can I just unplug it?
Thanks
 

Darius

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Sorry, but that's above my pay grade.

I just clean up around here.

d
(where'd I leave that broom?)

NICE PICTURE!!
 

5one9

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Is that a small hole in the middle?
 

Caddylackn

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Well that is a dilemma.

I am thinking this is a cheap aftermarket fuel pump that runs a greater range of years. They save money by just making one model for both return and non-return style. The original directions probably say "if you have a '77-81 cadillac with the _ _ motor and fuel return line, drill out return nipple with a _" diam. drill bit..."

You can run it without a return line, but if you do develop heat soak and vapor lock, you now know how to fix it.
 

Darius

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What Caddylackn said! :thumbup: :D

bro. d
 

48Austin

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Thanks for clearing that up fellas.
However, after reading your posts this morning, I went out to install my return line and what did I see?View attachment 25317
The return line fitting is plugged.
Is this normal, can I just unplug it?
Thanks
It appears that this pump does not have the big nut on it. Which IS actually where the fuel filter goes on Cad a/c cars from '68 on. This is why the pump body is so long. Takes the long paper filter. Don't believe me! Just take it out and see what falls out. Must be a generic pump that WILL make a/c cars vapor lock.
 
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