R2.8 Fuel Line Sizes

[TheDustyRag Junior Member Find all posts View Profile Close TheDustyRag]

Hi,

I'm doing an R2.8 install on my 1981 jeep scrambler and noticed something odd in the manual for fuel line sizes. In the manual it specifies that you should use 3/8" ID tubing for the supply line and 5/16" ID for the return.



This seems odd to me since tubing is measured by outside diameter.


Also the youtube video on fuel system at 4:40 says the supply line is 5/16" and return line is 1/4".

Anyone know what fuel line sizes are actually needed?

Thanks!

[97 TJ Junior Member Find all posts View Profile Close 97 TJ]

I used 3/8" for both supply and return. No issues.

[Sanders Senior Member Find all posts View Profile Close Sanders]

I believe I installed 5/16 for both. In theory you wouldn't need as large of diameter on the return as you should be leaving some fuel for the injectors to use. I think restriction on the fuel pump inlet is more problematic than lack of restriction on the return but I'm not an engineer!

On my current J-Truck project, I'm probably going the 5/16 route as well for both supply and return for simplicity if I need to carry some spare hose for a trail repair.

My only concern with 3/8" diameter would be that it could be taxing the lift pump by constantly pulling that extra volume of fuel through the line but someone smarter than me will likely use this as an opportunity to teach me fluid dynamics 101

[Digger Senior Member Find all posts View Profile Close Digger]

3/8" and 5/16" OD line diameters (respectively) will be fine. I'm using 3/8" both ways so I only had to buy one size of tubing. Not sure why it's called out as ID, since that is less common for fuel lines.

[TheDustyRag Junior Member Find all posts View Profile Close TheDustyRag]

Thanks for all the replies! I’m going to go with stock cj line sizes then (5/16” supply and 1/4” return)since that’s what the engine connectors and fuel tank sending unit are. If I run into any issues I’ll be sure to update.