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I believe the feed line in my fuel system has rotted.

If I'm going to cut out the rusted areas and splice a new line in...

  1. Is it best to flare a hardline?
    • Is steel the OEM material?
  2. How would I connect the two?
    • Compression fittings?

I'm confused about the options to do this.

Would rubber fuel hose work?

  1. Would rubber fuel hose work?
  2. Do I just use hose clamps?
  3. Should I flare the hard line first and slip the hose over it?
  4. Do rubber fuel hoses last a while?
  5. Can fuel seep through rubber hoses causing a gas smell?
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  • Compression fittings would be fine for this type of job you don't need to flare if you're only splicing in a line.
    – Ben
    Oct 30, 2016 at 15:54
  • Why does everything I read say not to use compression fittings for fuel line?
    – ohmmy
    Oct 30, 2016 at 21:54
  • You'd have to provide a source. Compression fittings are fine for low pressure steel lines like fuel pump lines. This probably depends more on where you live and what you're vehicle inspection entails.
    – Ben
    Oct 30, 2016 at 22:42
  • I've read it on various forums saying they're not recommended on high pressure lines like fuel. Maybe they meant fuel lines that aren't stock? Are there any other types of fittings that could be used to connect one line to another?
    – ohmmy
    Oct 30, 2016 at 22:49
  • fuel pressure typically reaches 60 psi at most on non gdi systems. compression fittings hold in the hundreds of psi. if you're splicing the line either use compression fittings or flare the line with new fittings and unions.
    – Ben
    Oct 31, 2016 at 1:06

3 Answers 3

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To be honest, if part of the fuel line is rotten, I'd be tempted to replace the whole line - chances are the rest isn't far behind...

Modern rubber hoses should last a decent amount of time, they're made of better rubber than they used to be, and are reinforced to take the extra pressure of modern injection systems.

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  • Yeah thing is on my car 98 civic the subframe needs to come down to replace all the lines and shops quoted a lot of money and I don't think I could tackle that on my own. Is it true rubber hoses will seep gas causing a smell? And just for reference are AN fittings only used on rubber hoses?
    – ohmmy
    Oct 30, 2016 at 13:02
  • never heard of seeping when using fuel line rated rubber. AN can be used on others too.
    – chris Frisina
    Oct 30, 2016 at 14:41
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    We don't know what country you are in, but in the UK any leak in the fuel system, or part of fuel tank and lines in "poor condition", will fail the annual MOT safety inspection. I would expect any "non-standard" repair job would with "improvised" joints would be considered as "poor condition". That's aside from issues like a failure spraying fuel over a hot engine, fuel vapor getting inside the car and being ignited by a cigarette, etc. There are some things you should never play with, and gasoline is one of them!
    – alephzero
    Oct 30, 2016 at 15:55
  • @chrisFrisina are AN fittings better? I'm having a hard time understanding why people use them
    – ohmmy
    Oct 30, 2016 at 16:02
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I've had to deal with rotten fuel lines on my '94 Nissan. Took me a year to find a suitable solution.

Like you, I was considering steel lines to replace the entire thing, but the steel lines I found were shorter than what I needed, so I needed to splice several lengths together. The issue I had was how to splice them together. The sections I could buy didn't have a connector on the ends, and the tools I could find for flaring and crimping were not inspiring my confidence, as they were:

  • stretching the already thin metal in order to make the flared end
  • the tool was leaving deep teeth marks in the already thin metal
  • both ends were fitting rather clumsily and I could guarantee they would leak.

I spent most of that year looking for a proper tool that would do this to my satisfaction, did't find one. What I did find instead is a shop that sold all kinds of lines cut to your length with whatever connector you needed. Sure, they had steel lines, which are hard to bend without crimping. They also had some copper alloy you could bend with your bare hands and won't rust as quick as steel lines. $120 for all 3 fuel lines and they made them in about 10 minutes while I waited, complete with the ends I needed. Each line was one solid piece.

Of course, when I got in there to remove the original fuel lines, I got an eyeball on the brake lines and I got scared. Went back to the shop, $140, now I got both runs of brake lines for the rear brakes. Brand spanking new from the firewall to the rear struts.

Find a hose shop near you. Google for "brake lines," "hydraulic lines," that's the kind of shop you want. They make stuff for industrial applications mostly, but their tools and materials can handle automotive as well.

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  • What's the best connector to use for splicing in a line? I'm confused about the different types available and what application
    – ohmmy
    Oct 30, 2016 at 16:03
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    There isn't really a "best connector." Different manufacturers use different things. If you are going with a solid line, I'd get a connector that screws in and put thread-locking compound on it. If you are going with a rubber hose, just get an end that has a "rib" on it, so the screw-clamp that you would use has something holding it on.
    – tlhIngan
    Oct 30, 2016 at 22:51
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The absolute best way is to replace the entire steel line. When this isn't possible, use as much steel as you can and as little fuel injection rated hose as possible. The issue with rubber hose is that it will seep fuel if the outside of the steel line is rusty or has a rough uneven surface. Find a clean area with minimal rust. If you can flare the end, the connection with the hose will be more secure. Use the more expensive fuel injection clamps. Replace as much of the rusted area with steel as possible. Make the last connection with rubber hose. Again flare the ends and use just enough hose to make a secure connection, generally less than six inches in length. The hose will deteriorate over time and should be inspected at least annually.

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9
  • Thank you, you mean flare the end and slip the rubber hose over and clamp it down? What fittings would I use to connect steel lines together? Also why do people switch to stainless steel rubber fuel lines if the longevity isn't as long as steel?
    – ohmmy
    Oct 31, 2016 at 0:05
  • A hose clamped on a straight non flared steel line can slip off. It is less likely if flared as the clamp can't pass over the flare. If you are referring to steel braid covered hose (popular in performance applications) the advantages are easier installation and replacement of larger than stock diameter lines. Fewer potential fittings to loosen, the "WOW" factor. In cases where fittings are disassembled frequently (between race tear downs) they are more durable.
    – mikes
    Oct 31, 2016 at 0:27
  • Nice makes sense. I notice the stock oem setup uses small sections of rubber hose to connect regulator to the steel return line and from the fuel pump to steel main line. They've been on the car since it was new. Are these a different rubber that last longer or? Also I'm curious what would happen if a piece of steel line was used for an area but the wrong size (either smaller or bigger in diameter) would it mess up fuel pressure or affect performance?
    – ohmmy
    Oct 31, 2016 at 0:35
  • Slightly larger is likely not an issue. Too small could potentially starve the engine of fuel during high demand.
    – mikes
    Oct 31, 2016 at 0:38
  • Thanks man and if I'm connecting steel line to steel line what fitting should I use?
    – ohmmy
    Oct 31, 2016 at 0:44

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