This is what a guy on one of the forums had to say.
Chemist checking in. Alcohols are not necessarily more corrosive to rubbers etc., it is just that cars were designed to withstand petrol, not alcohols. All the gaskets etc. can be reformulated to withstand alcohols and in modern cars often are.
Some metals such as magnesium and possibly aluminium alloys are corroded faster by alcohols than water. This is probably because water initially gives a tight oxide protective layer after the initial attack. Alcohols do not and the corrosive attack (essentially metal + alcohol = soluble metal alkoxide) continues. To stop this, a little water is added to the alcohols which restores the oxide layer.
Some ideas of my own.
A simple fact about Ethanol. Ethanol on its own is hygroscopic, in other words it attracts and absorbs water from the air. If you accept the above that a little water would help prevent it from promoting the corrosion of aluminium parts you might think this is a good thing. The addition of a little water would promote the corrosion of steel parts. Apparently once the ethanol absorbs some water it starts to lose its solubility in the Gasoline and the fuel could separate so adding a little water won’t work in a blended fuel anyway. Ethanol produced and sold as fuel should have corrosion inhibiting additives in it but I’m not sure these are effective for aluminium.
Ethanol has a PH that is very similar to water so its acidity shouldn’t promote corrosion of either steel or aluminium parts. If it was mildly alkaline this would probably be better for inhibiting corrosion but it isn’t.
Ethanol is also a polar molecule like water but with a polar and a non polar end allowing it to mix with both polar and non polar substances though not at the same time it would seem.
Someone said; -
In fact the US Department of Energy’s Oak Ridge National Laboratory warns against the use of Zinc or Aluminium with Ethanol.
How true is this statement?
An extract from one of their reports!
3.3 METALS COMPATIBILITY
Some testing has shown that aluminum and brass are not appreciably affected by ethanol blends, although inconsistent or conflicting results are found.3–5 Steel tanks and fuel lines have demonstrated rusting over long-term use and severe pitting if exposed to mixtures of water and ethanol that have separated from a gasoline-ethanol blend.1,3 Use of appropriate corrosion inhibitors has been shown to prevent long-term rusting due to normal use.1 Magnesium is highly corroded by contact with ethanol in ethanol blends and should be avoided as a fuel system material.2 (No evidence of magnesium use in fuel systems was discovered in the course of this effort.)
Note; - this study was for E20.
Further comment from the study.
Testing was conducted with both unleaded and leaded gasoline as well as those two fuels mixed with 20 vol % ethanol and 1 vol % corrosive water. * Test temperatures were maintained at 55 ± 2°C (131°F) for metals, elastomers, and plastics. The components were immersed for up to 2000 hours. Testing determined that several metallic fuel system components were significantly degraded from contact with E20. Rust was found on metal surfaces in/on electric fuel pumps, fuel injectors, and fuel regulator diaphragms (see Figs. 3.5–3.7). The potential exists for the rust to become dislodged and clog fuel filters or settle in areas where mechanical components move, increasing wear rates. Accelerating the wear rate of bearings may lead to premature failure of components in these items. The fuel pump’s aluminium casing was found to be vulnerable to pitting from immersion in E20 (see Fig. 3.8). Pitting was also found on aluminium surfaces of carburettors (see Fig. 3.9). Corrosion products from this pitting could block fuel metering devices, which in turn could lead to engine stalling and/or deteriorated driveability.
Tarnishing of brass and copper components increased when they were immersed in E20. In parts such as the fuel pump commutator, armature, and brushes, the corrosion products could increase wear rates, leading to premature component failure. These copper and brass pieces also carry current. If excessive corrosion were to collect on these parts, resistance could increase, causing decreases in fuel pump speed and pressure output, which in turn will limit engine output and vehicle performance.
They say aluminium is not appreciably affected yet have some corroded aluminium parts. Note; - 5xxx and 6xxx aluminium alloys are aluminium magnesium and aluminium magnesium silicon alloys respectively.I would think if magnesium is such a problem you should avoid these particular alloys.