The short answer
For molded parts in gasoline or diesel, acetal copolymer is the standard. PA11 and PA12 are the fuel line nylons, usually with a fluoropolymer or EVOH barrier layer. Glass-filled nylon 66 and 6 are the workhorses for hot motor oil and transmission fluid. PPS, PVDF and fluoropolymers handle the hottest and most aggressive fuels. HDPE makes good fuel tanks only with a barrier layer, because fuel permeates through it. Keep ABS, polycarbonate, polystyrene, acrylic and flexible PVC away from fuel.
Fuels and oils are mostly hydrocarbons, which semi-crystalline plastics resist well and amorphous plastics often do not. Additives, alcohol, heat and stress all change the picture, so test parts in the actual fluid at the actual temperature. For general chemical resistance see chemical-resistant plastics.
The fluids
- Gasoline contains aromatic hydrocarbons (toluene, xylene) that swell or crack amorphous plastics. Most U.S. pump gasoline is E10 (up to 10% ethanol), and E15 and E85 are also sold.
- Ethanol and methanol increase permeation through many plastics and barrier layers, swell some nylons and attack some elastomers. Methanol blends are harsher than ethanol blends.
- Diesel is heavier and less aggressive to plastics than gasoline, but fuel return lines run hot.
- Biodiesel (fatty acid methyl esters) is a stronger solvent than diesel, swells some elastomers and can oxidize into acidic products as it ages.
- Motor oil, transmission fluid (ATF) and gear oil are generally mild at room temperature, but can run at about 100–150°C (212–302°F) in service, and their additives become more aggressive when hot and aged.
- Hydraulic fluid: mineral-oil types are mild. Phosphate ester fire-resistant fluids attack PC, ABS, PVC and many seal elastomers.
Permeation vs. chemical attack
These are different failures. Chemical attack damages the plastic: it swells, softens, crazes, cracks or loses strength. Permeation is fuel dissolving into an intact wall and evaporating from the outside. The part is fine, but it leaks vapor.
HDPE shows the difference. It resists gasoline attack and is tough and cheap, but hydrocarbons permeate it readily. Automotive HDPE tanks are therefore coextruded with a thin EVOH barrier layer held between HDPE layers by tie layers, or the tank surface is fluorinated. Ethanol makes EVOH less effective (one modeling study of a typical multilayer wall found it roughly doubled permeation), which is one reason fuel systems are tested with ethanol blends. Fuel lines use the same idea: a PA12 outer wall with an inner layer of ETFE, PVDF or another barrier. Emission rules in the U.S. limit permeation from vehicle and small-engine fuel systems, so the finished tank or hose has to be tested, not just the resin.
Plastics for fuel and oil compared
| Resin | Gasoline / ethanol blends | Diesel / biodiesel | Hot oil, ATF, hydraulic (mineral) | Fuel permeation | Typical uses |
|---|---|---|---|---|---|
| Acetal copolymer (POM) | Very good; fuel grades for hot or aggressive fuel | Very good | Very good to about 100°C (212°F) | Low | Fuel pump modules, flanges, valves, caps, sender parts |
| PA11 / PA12 | Very good; slight swelling with alcohol blends | Very good | Very good | Moderate; barrier layers for low emission lines | Fuel lines, vapor lines, air brake tubing |
| PA66 / PA6, glass-filled and heat-stabilized | Good; some swelling in alcohol blends, more with methanol | Good | Excellent; hot oil is a core use | Moderate | Oil pans, valve covers, oil filter housings, fuel rails |
| PBT, glass-filled | Good at moderate temperatures | Good | Good | Low to moderate | Connectors, sensor housings; check hot, wet service |
| PPS, glass-filled | Excellent | Excellent | Excellent, including hot ATF | Low | Fuel pump parts, transmission and oil system parts |
| PVDF | Excellent, including alcohol blends | Excellent | Excellent | Very low | Fuel line liners, filters, chemical tubing |
| PTFE, FEP, ETFE | Excellent | Excellent | Excellent | Very low (ETFE used as fuel hose barrier) | Hose liners, seals, fuel line inner layers |
| HDPE | Good, swells slightly | Good | Good at moderate temperatures | High without a barrier; EVOH layer or fluorination needed | Fuel tanks (multilayer), cans, oil bottles |
| ABS, PC, PS, PMMA (avoid) | Poor: softens or stress-cracks | Fair to poor; biodiesel worse | Fair at best; stress-cracks with many oils | n/a | Keep away from fuel |
| Flexible PVC (avoid) | Poor: plasticizer extracted | Poor | Poor | n/a | Hardens and cracks |
General guidance for typical grades at moderate temperature. Resistance falls with heat, stress, aged or oxidized fluids and alcohol content, and individual grades vary. Test finished parts in the actual fluid and temperature, and check the data sheet for your grade.
The good choices
Acetal copolymer resists gasoline, diesel and alcohol blends with little swelling and is the usual material for fuel pump modules, flanges, valves and caps. Copolymer is preferred over homopolymer in fuel. Fuel-resistant grades are typically specified for continuous fuel contact up to about 100°C (212°F), and grades made for aggressive fuels are used where fuel recirculates hot or may be oxidized (“sour”). Acetal is attacked by strong acids, including some acidic cleaners. See acetal.
PA11 and PA12 absorb little water, stay flexible and resist fuels and oils, so they dominate fuel and vapor lines and truck air brake tubing. See nylon 11 and 12.
Nylon 66 and 6 resist oils and greases very well, and glass-filled, heat-stabilized grades are standard for oil pans, valve covers, oil filter housings and many fuel rails. They absorb some alcohol from blended fuels and swell slightly, more so with methanol. See best plastic for under-hood parts.
PPS resists almost every fuel and oil below about 200°C (392°F) and keeps its dimensions, so it is used for fuel pump components and hot transmission parts. See PPS. PVDF and the fully fluorinated resins (PTFE, FEP, PFA) and ETFE resist essentially all fuels, including high-alcohol blends, and are used as liners and barrier layers. See PVDF and fluoropolymers.
PBT, usually glass-filled, resists gasoline and oils at moderate temperatures and is used for connectors and sensor housings near fuel. It hydrolyzes in hot, wet conditions, so check that before using it in a hot fuel or coolant zone.
The poor choices
- ABS, polystyrene and acrylic soften, craze or dissolve in gasoline.
- Polycarbonate and PC/ABS stress-crack in gasoline and many oils, often at a screw boss or press fit. See environmental stress cracking.
- Flexible PVC loses plasticizer to oils and fuels and turns stiff and brittle. Rigid PVC is attacked by aromatic hydrocarbons.
- Elastomers: natural rubber, SBR and EPDM swell badly in petroleum fuels and oils. Nitrile is the usual oil seal material, and fluoroelastomers handle fuels with ethanol. Many styrenic TPEs swell in oil; polyester TPU and copolyester TPE do much better. Phosphate ester hydraulic fluid is the reverse case, where EPDM is often used and nitrile is not.
What to send us for a quote
- The grade you run now, or the part and what it does
- The exact fluid: gasoline blend (E10, E15, E85), diesel or biodiesel blend, oil or hydraulic fluid type
- Temperature range, and whether contact is constant, splash or vapor
- Permeation limits or OEM material specifications, if any
- Quantity for this order and per year, and ship-to city
Common questions
What plastic is best for gasoline contact?
Acetal copolymer is the standard for molded fuel system parts such as pump modules, flanges and valves. PA11 and PA12 are used for fuel lines, often with fluoropolymer or EVOH barrier layers, and HDPE with an EVOH barrier layer is used for fuel tanks. PPS, PVDF and fluoropolymers handle the most demanding conditions.
What plastic is resistant to motor oil?
Nylon 66 and nylon 6, especially glass-filled and heat-stabilized grades, are the usual choice for hot oil parts such as oil pans, valve covers and filter housings. Acetal, PBT, PPS and PEEK also resist oils well.
Which plastics does gasoline attack?
ABS, polycarbonate, polystyrene and acrylic are softened or stress-cracked by gasoline. Flexible PVC loses plasticizer, and natural rubber and EPDM swell. Polyethylene swells slightly but is still used for tanks with a barrier layer.
Does ethanol in fuel affect plastics?
Yes. Ethanol increases fuel permeation through many plastics and barrier layers, swells some nylons slightly and attacks some elastomers. Parts for E10, E15 or E85 should be tested in that blend, not just in gasoline.
What is the difference between permeation and chemical attack?
Chemical attack damages the plastic: swelling, softening, cracking or loss of strength. Permeation is fuel passing through an intact wall as vapor. HDPE resists gasoline attack well but lets fuel permeate, which is why fuel tanks need a barrier layer.
Is acetal good for diesel fuel?
Yes. Acetal copolymer is widely used in diesel and gasoline systems. Fuel-resistant grades are typically specified for continuous fuel contact up to about 100°C (212°F); for hot recirculating fuel or oxidized fuel, ask for a grade made for aggressive fuels.
Can PVC be used for fuel or oil?
Rigid PVC resists some oils but is attacked by aromatic hydrocarbons in gasoline. Flexible PVC is a poor choice because oils and fuels extract its plasticizer, leaving it stiff, shrunken and cracked.
Tell us the fluid and the part
A polymer chemist reviews every request, then matches your grade or finds a qualified equivalent and prices it.
What to send for an accurate quote
- The grade name, from any supplier, or a data sheet
- Color (natural, black or a custom match)
- Fill type and percentage, if any
- Melt flow, if you know it
- Quantity for this order and what you use in a year
- Ship-to city and state or province