Replace every natural-rubber, neoprene and unknown-plastic part in an ethanol fuel system with Viton, PTFE (Teflon), polyethylene or stainless steel, because ethanol swells, softens and leaks through the others. Before trusting a salvaged hose or gasket, soak a piece in the fuel for a day or two and reject it if it swells, softens, turns sticky or discolours the liquid.
Part of Ethanol Fuel Production
Fuel line material compatibility is matching hoses, seals, gaskets and tanks to ethanol, which dissolves or swells many materials that suit gasoline.
A Leak Is A Fire, So The Material Is A Safety Decision
The parent lists the materials: ethanol attacks natural rubber, neoprene and some plastics, and Viton, Teflon (PTFE), polyethylene and stainless steel are compatible. It also warns that methanol is corrosive to aluminium. Ethanol is a good solvent for resins and varnishes as well, so it can loosen old deposits in a tank and send them into filters; plan on cleaning the system before the first fill and fitting a filter that can be changed.
| Material | Verdict | Note |
|---|---|---|
| Viton, PTFE | suitable | the parent’s recommendation |
| Polyethylene | suitable for lines | slow permeation of ethanol through the wall, so do not store ethanol in it long term (parent) |
| Stainless steel | suitable | best for rigid lines and tanks |
| Natural rubber, neoprene | unsuitable | swells and softens (parent) |
| Unknown plastics | test first | some are “attacked” (parent) |
| Aluminium | suspect | methanol corrodes it (parent); wet ethanol is also reported to attack aluminium and zinc, recalled, test pieces first |
The corpus’s own guide to improvised seals recommends rubber, leather and cork gaskets (Gaskets and Seals). Those suit water and many oils; for an ethanol system treat them as unsuitable until they pass the soak test below.
What You Need
- Small samples of each candidate hose, seal and gasket
- A glass jar with a lid and a sample of the actual fuel
- A scale or a ruler, to see changes
- Replacement materials from the suitable list, including a metal tube for rigid runs
Method: The Soak Test
Step 1: Weigh or measure the sample.
Step 2: Immerse it fully in the fuel in a lidded jar kept in a cool, safe place away from flame.
Step 3: Look after one day and again after two. Reject it if it swells, softens, goes tacky, crumbles, or turns the fuel cloudy or coloured. A material that is still firm and the same size is a candidate.
Step 4: Dry and re-measure. Any lasting change in size or weight is a warning even if the sample looks fine.
Method: Choosing Parts
Step 1: Prefer rigid stainless or copper tube for long runs, with short flexible sections of Viton or approved hose only where movement requires them.
Step 2: Make joints with PTFE tape or thread-sealing compound proven by the soak test, and avoid cork floats and leather washers in carburettors.
Step 3: Inspect every flexible part regularly. Replace at the first sign of cracking, swelling or weeping.
Common Mistakes
- Reusing a gasoline hose because it is flexible. It may be neoprene or natural rubber and last only weeks.
- Storing ethanol in polyethylene for months, which slowly loses ethanol through the wall.
- Using salvaged fuel line without a test. Pipe that carried fuel for another use may hold residues and cannot be assumed compatible (Salvaged Modern Pipe warns against reusing anything that carried fuel or chemicals for water).
A weeping hose is a fire
Ethanol’s flash point is 13°C, so a leak on a hot engine can ignite at room temperature, with a nearly invisible flame. Never run an engine with a visibly damp line; check by eye and by touch with the engine off and cold.
What’s Next
- Learn next: Fire Safety, for what to do when it burns
- Combine with: Carburetor & Injection Modifications, the other half of preparing an engine