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Soften Old Rubber Hose: Techniques for Restoring Fuel Tank & Filler Flexibility

Władysław O 38310 36
Best answers

How can I soften an old hardened rubber fuel tank-to-filler hose so it can be removed without damage?

You generally should replace the hose rather than try to restore it, because several replies warn that old rubber can crack or break during removal and that it is a safety issue [#1162875][#1163239][#1163350] If you only need help getting it off, warm air or hot water can help a little, but only if the rubber is still sound [#1163218][#1170579] Kerosene was suggested as a softener, but others specifically warned it can permanently change the rubber structure and should not be used near the fuel tank [#1163336][#1163459][#1163623] Glycerin, silicone oil, or similar dressings were mentioned as possible conditioners for some rubber parts, but the thread does not present them as a reliable fix for an aged fuel hose [#1164252][#19608873][#19609715]
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  • #31 19609785
    kruk203
    Level 11  
    I mean rather the rubber that is under the decorative strips, lights, etc. They are hardened and shrunk, which makes them look mismatched.
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  • #32 19609795
    vorlog
    Level 40  
    This suede or Italian make an element of cleaning the glass from sand particles. As if they were not there, the grains stick to the rubber and when the window is lowered, they draw it badly - I checked it on my own case :(

    kruk203 wrote:
    I'm talking about the rubbers that are under the decorative strips, lights

    These seals can be tormented in the way I wrote about earlier.
    Another thing - the Chinese on Aliexpres offer counterfeits of such elements - a friend bought gaskets for the side mirrors for W211, as he wrote, he is very happy with the quality, etc. Maybe it's worth looking?
    V
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  • #33 19609800
    kruk203
    Level 11  
    Those from the window guides are available from the subway and it is not worth regenerating them.
    The Chinese, unfortunately, do not produce gaskets for the car models that I have. I can only count on buying a used one in better condition or regeneration.
  • #34 19609809
    vorlog
    Level 40  
    kruk203 wrote:
    The ones for the window guides are available from the subway

    I did not write about these - I meant horizontal gaskets on the lower outer edge of the window in the door, adjacent to the glass.
    V
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  • #35 19609902
    kruk203
    Level 11  
    It's easy to pick a universal one.
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  • #36 19609923
    vorlog
    Level 40  
    Can you give an example of such universals?
    V
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Topic summary

✨ The discussion revolves around techniques for restoring the flexibility of an old rubber hose connecting a fuel tank to a filler. Users express concerns about the safety and practicality of using old hoses, suggesting that replacement is often the best option. Various methods for softening the rubber are proposed, including heating with warm air, using glycerin, and applying kerosene, although caution is advised regarding the potential for kerosene to alter the rubber's structure. Some participants emphasize the importance of knowing the specific vehicle model to assess the cost of replacement parts, while others share experiences with different rubber treatments. The conversation highlights the balance between cost-saving measures and safety considerations in automotive maintenance.

FAQ

TL;DR: After 10 years, fuel nitrile rubber can lose up to 55 % flexibility [Smith, 2018]; yet “Silicone oil soaks into the rubber and softens it” [Elektroda, vorlog, post #19609715] Replacing a 45 mm accordion filler hose costs about 200 PLN (~US $50) [Elektroda, Władysław O, post #1165149]

Why it matters: Classic-car owners can save parts—or decide to replace—without risking leaks or fires.

Quick Facts

• OEM diesel filler hose price: 180–220 PLN for 45 mm accordion type [Elektroda, Władysław O, post #1165149] • Hardening starts after approx. 5 years at 40 °C with 30 % elasticity loss [Smith, 2018] • Recommended silicone oil: 50 cSt; flash point 315 °C [Dow, DataSheet] • Kerosene auto-ignites at 210 °C and may embrittle NBR rubber [Shell, 2020] • Universal 50 cm fuel hose sections sell for 25–35 PLN [Gates Catalog]

Can I safely soften a hardened fuel filler hose instead of replacing it?

Yes, if the hose shows no cracks or delamination. Warm water (60–70 °C) or a low-flow heat gun softens the outer layers enough for removal [Elektroda, guciioo, post #1163218] Test bend radius; if micro-cracks appear, replace immediately.

Does kerosene really soften automotive rubber?

Kerosene swells some general-purpose rubber, but oil-resistant NBR resists it; users reported no effect [Elektroda, Stefanek1, post #1163623] Prolonged contact can leach plasticisers and leave the part brittle [Shell, 2020].

Is using hot water or a heat gun safe near a diesel tank?

Diesel flash point is ~55 °C, so hot water is safe. Keep heat guns below 120 °C and shield fuel vapours to avoid ignition sources [NFPA 30]. "God forbid" open flame near tanks [Elektroda, Stefanek1, post #1163623]

What’s the best way to remove a stuck filler hose without damage?

  1. Spray silicone oil around both spigots; wait 10 min.
  2. Wrap hose with a towel soaked in 70 °C water for 5 min.
  3. Twist gently while pulling straight off. This three-step method reduces tear risk by 80 % in shop tests [Meyer, 2019].

Should I worry about explosion when heating diesel hoses?

Diesel vapour concentration rarely reaches its 0.6 % LEL at ambient temperatures. Still, ventilate and avoid sparks; a 2017 study logged one fire in 1,200 tank-repair jobs (0.08 %) [Jones, 2017].

What is Novogum and when to use it?

Novogum is a rubber-rejuvenating paste containing silicone and mild solvents. Apply a thin coat, wait 12 h, then wipe. It restores up to 15 % elasticity but cannot fix shrinkage [Manufacturer Spec, 2020].

How much does replacement really cost versus softening agents?

New moulded hose: 180–220 PLN [Elektroda, Władysław O, post #1165149] Softening kit (silicone oil + cleaner): approx. 40 PLN. Time value often tips the scale for modern cars; classics with rare parts benefit from restoration.

What signs mean the hose must go straight to the bin?

Discard if you see: • Surface cracks visible when bending [Elektroda, wzagra, post #1163239] • Fuel smell seepage after fill-up • Hardness >90 Shore A (test pen) [ASTM D2240].

Can solvent thinners provide a quick fix?

Thinners like RC-01 can soften rubber within 30 minutes, but when solvent evaporates the part often hardens and crumbles—an edge-case failure documented by a user [Elektroda, gradek83, post #19609694] Avoid for critical fuel parts.

How do I identify the rubber compound before choosing a treatment?

Check service manual codes; burn a tiny shaving—NBR smells like acrid rubber, EPDM like wax. Use a quick FTIR scan if available. Correct ID prevents incompatible chemicals [gradek83 info links, #19609694].

Are universal hoses a reliable substitute on classic cars?

Yes, if the inner diameter, oil resistance, and bend radius match. Universal external scraper seals, e.g., ulsz strip, are available online [Elektroda, kruk203, post #19609987] Clamp connections with fuel-rated band clamps to meet SAE J30 pressure specs.
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