Pros and Cons of fuel return line...

[wilkin250r]

So my street-ready restoration project is nearing some final details. It's a 72, but I don't think the tank is original because it was my understanding that 72 had a vent line on the top of the tank, and mine certainly does not.

However, it DOES have a return line that is currently just hanging out in the engine bay, and pukes fuel if you fill the tank up all the way. I assume it was originally hooked to a fuel pump with a return line, but that fuel pump left eons ago with the old engine. Current fuel pump has no provisions for a return.

I've heard of people hooking up the return line to a "T" fitting with a small orifice, and this logic makes sense. I can certainly see this eliminating vapor lock at the carb. Am I more likely to get vapor lock from tank to pump, or pump to carb?

So my options would be to just plug the line, replace the fuel pump with one designed for a return line, or hook it up near the carb with a "T" fitting.

[GASoline71]

I eliminated the return line on my 1972 GMC C15 and capped it off at the tank. I left the EEC hooked up and use it as a vent along the passenger side frame rail. I also switched to a vented fuel cap, just in case.

Gary

[Steeveedee]

Vapor lock occurs in the suction line from the tank to the pump. If it were mine, I'd use the recirc line style fuel pump. I have a small booster electric fuel pump to pressurize the fuel pump suction line to reduce vapor lock, since my truck does not have a recirc line.

[rjs53]

I would keep it. You could cap it off and make a vent out of it like gasoline said. If you ever decided to do an grade in the future and needed more fuel you'll already have a return line.

[El Dorado Jim]

Originally Posted by Steeveedee

Vapor lock occurs in the suction line from the tank to the pump. If it were mine, I'd use the recirc line style fuel pump. I have a small booster electric fuel pump to pressurize the fuel pump suction line to reduce vapor lock, since my truck does not have a recirc line.

x2 get a fuel pump that has the return line, it will keep from getting vaporlock, I did this on my son's truck

[71CHEVYSHORTBED402]

I'm restoring mine without the return line, which is 71 prior. Takes a different gas cap than 72 too. It didn't have a return when I first got the truck, and never locked up. If it vapor locks I guess I'll need new from the sender to the carb.......Fun.

[68 P.O.S.]

On my 72 I installed an Edelbrock fuel pump that doesn't have a return line. All I had to do was cap off the return line and add a vented gas cap.

[71CHEVYSHORTBED402]

I wonder how many of "us" don't have a return line and experienced vapor lock?

[68 P.O.S.]

Not it

[Steeveedee]

Originally Posted by 71CHEVYSHORTBED402

I wonder how many of "us" don't have a return line and experienced vapor lock?

My '70 does not have a recirc line, and if it gets hot enough it will vapor lock. Running the electric fuel pump to pressurize the fuel to the pump helps. It was hot out, but I wasn't even using the AC. It's why I'm nailing every opportunity for cooler running. That specific case, the fan clutch had given up the ghost, though.

[GASoline71]

Originally Posted by 71CHEVYSHORTBED402

I wonder how many of "us" don't have a return line and experienced vapor lock?

I was thinking the same thing. I've been playing with GM trucks and cars for many years and have never had to use a return line for any reason. Not saying that some might need to use a return line for whatever reason. But in my experience, i have eliminated the return line (usually becuase I have insyalled a performance mechanical fuel pump) and have just switched to a vented gas cap, and wah-lah...

Gary

[71CHEVYSHORTBED402]

Originally Posted by GASoline71

I was thinking the same thing. I've been playing with GM trucks and cars for many years and have never had to use a return line for any reason. Not saying that some might need to use a return line for whatever reason. But in my experience, i have eliminated the return line (usually becuase I have insyalled a performance mechanical fuel pump) and have just switched to a vented gas cap, and wah-lah...

Gary

What's a performance mechanical pump Gary, can you be more specific?

[gvw5400]

My experience was the same as GASolene71, but that was in the days before ethanol
was added to everything. It is much more difficult to drive anything carbed now.
My truck Will vapor lock if it gets in ANY town traffic,( two red lights and party over)
After finding a alcohol free fuel source it has no issues at all!
But it's a giant PIT* to have Two stations within 40 miles to fuel from.
All the Best, Dirk

[71CHEVYSHORTBED402]

Originally Posted by gvw5400

My experience was the same as GASolene71, but that was in the days before ethanol
was added to everything. It is much more difficult to drive anything carbed now.
My truck Will vapor lock if it gets in ANY town traffic,( two red lights and party over)
After finding a alcohol free fuel source it has no issues at all!
But it's a giant PIT* to have Two stations within 40 miles to fuel from.
All the Best, Dirk

Don't know how accurate this site is, but..................https://www.pure-gas.org/index.jsp?stateprov=NV

[gvw5400]

71Chevyshortbed402
The puregas site is good and accurate for the most part in Colorado.
I'm curious about the EEC lines and routing also, My 71 350 has the carbon canister and lines but not the return line at the pump.
If I can make sense of it, some repurposing may be in order! it would be great to refuel
anywhere and have a drivable truck in traffic!

[71CHEVYSHORTBED402]

Originally Posted by gvw5400

71Chevyshortbed402
The puregas site is good and accurate for the most part in Colorado.
I'm curious about the EEC lines and routing also, My 71 350 has the carbon canister and lines but not the return line at the pump.
If I can make sense of it, some repurposing may be in order! it would be great to refuel
anywhere and have a drivable truck in traffic!

They didn't put in return lines until 72. Speaking for a 72 402, per the parts book they were required for TH transmissions only. I'm still on the fence.

[gvw5400]

I guess that's why my 71 doesn't have a return line !
That's for the info.
It's one more piece of the puzzle.
All the Best, Dirk

[71CHEVYSHORTBED402]

Originally Posted by gvw5400

I guess that's why my 71 doesn't have a return line !
That's for the info.
It's one more piece of the puzzle.
All the Best, Dirk

I think someone mentioned some SBC had them pre-72. Not sure on that, but the parts book would verify. Edit: I just checked, and 350 didn't have one. In 72 they did for TH transmissions, same as 402.

I'd like to pass on one that's for sure. If there's something to ethanol content, I'll never drive this truck long distances anyway. But then we're at the mercy of how long low-ethanol remains available.

[GASoline71]

Originally Posted by 71CHEVYSHORTBED402

What's a performance mechanical pump Gary, can you be more specific?

Yep... aftermarket fuel pumps that put out more GPH and a tad more pressure than stock. I have used Carter "street" (now "muscle car") and "strip" mechanical fuel pumps for ages.

Gary

[71CHEVYSHORTBED402]

Originally Posted by GASoline71

Yep... aftermarket fuel pumps that put out more GPH and a tad more pressure than stock. I have used Carter "street" (now "muscle car") and "strip" mechanical fuel pumps for ages.

Gary

Thanks Gary