Fuel line questions

[MA74CJ5]

I’ve been doing a ton of research on fuel lines for my 70 CJ5 with a V6 and a factory rear mounted fuel tank. A couple questions have come up. First, the under hood steel and rubber lines are all still intact however, the lines running under the body to the rear tank appeared to be plastic or nylon. Is that accurate? I’ve never seen a factory set up that didn’t use steel lines along the frame rails but my experience has been mostly CJs 72 and up. Second, can somebody confirm that the sizes are 5/16” for the feed and 1/4” for the return to the pump. Lastly, there’s a picture in the service manual, but it’s not that clear and I haven’t found anything online so does anyone have any photos of how the lines are run to the fuel tank and secured on the frame/under the body?

Thanks.

 

[FinoCJ]

the lines running under the body to the rear tank appeared to be plastic or nylon. Is that accurate?

This correct for my jan 70 albeit with under seat tank

can somebody confirm that the sizes are 5/16” for the feed and 1/4” for the return to the pump

Yes

 

[Kaiserjeeps]

My 69 CJ-5 had some nylon on it. Long gone but it was there. I just finished a 68 m715 ground up build. I will start it probably in two days. One of the things I did after seeing such a short life span on typical new rubber fuel lines, was to buy marine grade fuel lines. Our old jeeps had rubber lines that lasted for decades. Now they seem to check, crack and split after just a few years. So I have been buying marine lines because there are more stringent requirements for boat stuff. So far I think it was worth it. If they made quality rubber lines still, that would be fine. But stuff now days is garbage. And keeping fuel contained is a good thing. Just food for thought if you are not doing a restoration for originality. And ditto on the 5/16 feed and 1/4 return.

 

[jeepstar]

Why not use steel fuel line?

 

[timgr]

JMO - the Jeep is its own best reference.
I recall my new '73 had at the minimum vapor return lines in green nylon, and may have had nylon fuel return too.
A bit surprised that the feed line is nylon.
Note that modern Fords use nylon line for EFI that operates under significant internal pressure.
These lines are expanded to go over fittings at each end.

 

[MA74CJ5]

Thanks for the responses.
I agree on the marine lines, especially from the main line to the tank and under hood to the main line.

JMO - the Jeep is its own best reference.
I recall my new '73 had at the minimum vapor return lines in green nylon, and may have had nylon fuel return too.
A bit surprised that the feed line is nylon.
Note that modern Fords use nylon line for EFI that operates under significant internal pressure.
These lines are expanded to go over fittings at each end.

Currently the Jeep has nylon return and main fuel lines but it’s hard to use it as a reference because I don’t know what it originally came with. The jeep is from the West Coast, has zero rot or rust on it and is quite original. However, the tank has been replaced, and the lines may have been replaced with it. From my reading and these replies, it sounds like they very well may have been nylon lines, it’s just hard for me to believe that the feed line is not steel. Also, both lines just appeared to be draped over the transmission on their way back to the tank, and not really secured.

 

[FinoCJ]

Also, both lines just appeared to be draped over the transmission on their way back to the tank, and not really secured.

That sounds about right....there are/were some foldable tabs on the underside of the body that sorta helped secure them.....in some ways, those plastic/nylon lines are pretty indestructible as they don't rust like metal and don't deteriorate like rubber. A little heat on them allows for a good connection to the tank/sending unit nipples etc.

 

[Fireball]

My '71 also has nylon feed and return lines from the fuel tank up to the back of the engine where metal lines run over the intake manifold and down to the fuel pump.

 

[Fireball]

I replace those line with these new ones a few years ago:

• https://www.amazon.com/dp/B07KVMBN4J?th=1
• https://www.amazon.com/dp/B074KD1DCH?th=1

The factory lines removed from the Jeep:

New lines:

You can see one of the clips on the body just above the bellhousing ear on the firewall in this picture:

The factory parts catalog is terribly lacking in details like size/length, but it does reference these as "flexible lines".

 

[jeepstar]

WHAT???!! IVE BEEN BENDING STEEL LINES ALL THESE YEARS??!

 

[Ol Fogie]

WHAT???!! IVE BEEN BENDING STEEL LINES ALL THESE YEARS??!

Can the steel fuel line be flared or a bubble to secure them to flexable hose with a clamp?

 

[timgr]

By flexible hose you mean rubber fuel hose to steel line?
If your kit does not include bubble flares, the usual is to do the first half of a double flare.
Start the double flare as usual but don't fold over the initial bulge on the end of the tubing.
If you mean nylon hose, the Dorman kit includes fittings to join the flexible hose to rigid tubing.

https://www.dormanproducts.com/p-27520-800-300.aspx

I presume these pieces are available individually if ytou look for them.
This kit includes a tool to stretch the end of the hose to fit over the various couplings.
I have connected the plastic couplings to the nylon hose by softening the hose with a heat gun and pushing over while soft.
Presume that would work ok.
There are also compression fittings in the Dorman kit that I presume could couple between nylion and steel or Nicopp.

 

[MA74CJ5]

That sounds about right....there are/were some foldable tabs on the underside of the body that sorta helped secure them.....in some ways, those plastic/nylon lines are pretty indestructible as they don't rust like metal and don't deteriorate like rubber. A little heat on them allows for a good connection to the tank/sending unit nipples etc.

Thanks for this info Fino very helpful!

Thank you Fireball for that picture. Now I know what to look for.

All this said I will be sticking with the nylon lines. I believe what I have is OEM. This jeep is almost 100% original. Gotta love the CA jeeps. You west coast guys got it so good!!

 

[MA74CJ5]

By flexible hose you mean rubber fuel hose to steel line?
If your kit does not include bubble flares, the usual is to do the first half of a double flare.
Start the double flare as usual but don't fold over the initial bulge on the end of the tubing.

This is what I've done for rubber to metal lines. Works great.

As for rubber to nylon this toolset looks good but its expensive. I believe the factory just ran rubber line over the nylon and put a spring clip on it correct?

That said, can anyone recommend good spring clips to use? There are tons on Amazon and ebay but im sure quality varies dramatically.

 

[colojeepguy]

I replace those line with these new ones a few years ago:

• https://www.amazon.com/dp/B07KVMBN4J?th=1
• https://www.amazon.com/dp/B074KD1DCH?th=1

The factory lines removed from the Jeep:

New lines:

You can see one of the clips on the body just above the bellhousing ear on the firewall in this picture:

The factory parts catalog is terribly lacking in details like size/length, but it does reference these as "flexible lines".

That's air line for a big truck, I've sold about a million feet of that over the years.
Is it really suitable for gasoline?

 

[dnb71R2]

Is it really suitable for gasoline?

I have the same question / concern.

 

[Fireball]

That's air line for a big truck, I've sold about a million feet of that over the years.
Is it really suitable for gasoline?

I did a bunch of research back when I swapped them out. From the parts manual:

The listing for the "TUBE, fuel assy. (Flexible line to fuel pump)" isn't helpful, but below that, the "USE THE FOLLOWING WHEN NYLON LINES ARE INSTALLED" give a clue to the material.

Nylon is fuel safe, and you'll notice the first Amazon listing says fuel or air. In fact one of the bags they came in explicitly says "Nylon Fuel Line":

Those Amazon lines have been on my Jeep for 4 years and 7000 miles now, and are doing fine. The only reason I replaced the originals was because the feed line had an abrasion over the transmission that was dripping.

All that said, If you're not comfortable with Nylon lines, bend up some NiCop metal lines and bubble flair the ends.

Also from the parts manual illustration, the rubber connector hoses are slid over the nylon and clamped. There were no flares on the ends of my factory Nylon lines. I think I slid mine in a couple inches before clamping for security:

 

[FinoCJ]

Also from the parts manual illustration, the rubber connector hoses are slid over the nylon and clamped. There were no flares on the ends of my factory Nylon lines. I think I slid mine in a couple inches before clammping for security:

that is how mine was done as well....

Is it really suitable for gasoline?

I think I am still running the OEM nylon lines for the front tank - just replace the short rubber connections every so often. They are pretty indestructible....and while they can get abrasion damage from rubbing, I think the rubber line is much worse. If you can get rid of the rubber connectors, it'll take decades to need replacement.

 

[colojeepguy]

The problem with the rubber connections is the crappy quality hose being sold these days. Ive been using fuel injection rated hose but I don't know if it's any better quality despite having a higher psi rating. I like the idea of the marine hose mentioned above, I may look into that.

 

[FinoCJ]

Ive been using fuel injection rated hose but I don't know if it's any better quality despite having a higher psi rating.

I did the same on my last replacement of the connections (I have some extra connections with the tank switching valve)....