What was the original 3rd gen F-body carbureted V8 fuel return line diameter? The places that sell the so-called "reproduction" fuel lines are selling 5/16" return lines for the carb equipped cars, the same diameter as fuel injected return lines, but shouldn't carbed cars' return lines be 1/4" like the return line port on the original style mechanical fuel pump is? Also, my GM G-body catalog shows 1/4" for carbed fuel lines, plus the picture in my 1986 Camaro assembly manual shows the return line being significantly smaller than the 3/8" fuel supply line.

 

In our cars, the return line was 5/16", the same as the port on the fuel pump.

It was ¼" in many older cars, esp those that the return originated off of the filter rather than the pump, but not ours.

There's no benefit to making it smaller.

 

Which fuel pump are you referring to? The Carter M6626, which is the mechanical fuel pump specified for carbureted 3rd gen f-bodies (and the other manufactures version of that pump) has a return port that is only 1/4" diameter. Are you sure you're not thinking of the fuel injected electric pump? There's no stock mechanical pump that I can find that has a return port of 5/16" as you said.

 

Go to the auto parts store and get a small sample of 1/4" I.D. fuel hose and 5/16" I.D. fuel hose. Then try slipping them over the end of your return line.
The size that fits will be the size your return line is.
Buy the length you need of that size...

 

He was answering your question about the return line on your car (and I believe he was correct, if your lines are original.)

Now the sizes you might find on your aftermarket replacement pump made in China or Mexico, yes that could be whatever size that manufacturer chose to use. BTW that pump you bought for your 1980s car also is made to fit a WIDE variety of other GM cars and trucks, probably spanning a period of at least 2 or 3 decades. So yes, it is no surprise if the line off your new pump is 1/4". It's okay, will still function just fine.

 

My aftermarket fuel pump I ordered online and it's NORS made in the US. It's not a made in China or Mexico pump you were referring to.

I don't think that GM would have used any different fuel pumps on 3rd gen F-bodies than they did for other makes getting the LG4 engines. I'm sure the same 305's that went into Firebirds and Camaros also made their way into Caprices and Monte Carlos.

Also, I don't understand what the point would have been to use as large as 5/16" fuel return lines on carbureted cars. I suspect very little fuel needs to returned to the tank with a carbed car using a mechanical fuel pump. Cars were made without fuel pumps with return ports for decades before they started using ones with return ports them in the late 70's. I suspect the extra return port was added to mechanical fuel pumps as much to help prevent vapor lock as anything else.

 

My 82 lg4 had 3/8 feed and 5/16 return. My dad had an 82 crossfire. It had the same size lines. Now I have 3/8 feed and returns cause that's what EFI needs. There is no reason to neck it down. 5/16 rubber line should fit on there. If not, something isn't right.

 

I still can't see the sense in using a 5/16" return line when a 1/4" one will work just fine, as evidenced by all the cars that have had 1/4" return lines.

 

What is your purpose in asking the question?

 

:shrug:

:shrug:

I thought you asked what size THE CAR has, not all that other know-it-all crap. Stay focused.

 

I just don't believe these cars ever had 5/16" fuel return lines when they had carburetors. It makes no sense at all.

 

Believe what you want, good luck w that!

 

Larger line, less restriction.
if you're doing a show or 100% correct restoration that requires the line to be 1/4" then pursue that. Especially if your car is 82-84. After that, it could be larger metric ( 5/16 =8mm) like a lot of other things that went metric in 84.5.
could be any number of reasons the f-car used different line than other cars. Does it matter that fuel gets back to tank faster with the bigger line?

 

The fuel will be cooler w the larger line, it's also less resistance on the pump (probably not an issue on stock power) The 5/16 is what was run in 82-84 v8 cars also, so a 100% resto would want period correct. The 3/8 looks larger than the 5/16 because it is. The sender in the tank has 3/8 and 5/16 lines coming out of it. So if you convert to 1/4, you're gonna need to neck it up somewhere.

 

Life is full of really hard decisions like whether you buy a perfectly functional 5/16" return line.

 

Haha!

 

I just mounted a new Carter M6626 (same make and part number you used) back in January on my 85 LG4. It was labeled made in Mexico. Not necessarily a bad thing. I think the return line on it was 1/4" as well. Been working fine for months that way so you should be fine too.