How long does it take for methanol to corrode metal?

Question

I race cars and they run off methanol. I have been told that if the methanol is left in the motor, it can begin to corrode the metal inside the motor causing damage. How long would it take until the methanol begins to corrode the metal?

Answer 1

I'm a corrosion engineer, so I might be able to help.

It's true, methanol acts as a weak acid, even in the pure anhydrous (dry) form.

Normally, ambient water is necessary to promote corrosion; in this case, methanol will create its own water from aluminum oxides, even in a sealed aluminum system.  Methanol is also hygroscopic and will absorb water from the air if the system is not sealed.

Interestingly, can act as its own oxidizer and a reduction agent,

and it can also strip the oxide layer off and corrode aluminum.  How long will it take before it begins to corrode the metal?:  This process starts immediately, but the rate is low.

Take note: It will cause certain plastics to swell that would otherwise be compatible with gasoline, so you have to check to be sure your tubes and seals are alcohol compatible.  Viton and other fluoroelastomers are OK with both gas and alcohol (but $$).  If you always run alcohol, there are less expensive alcohol-compatible plastics.

My experience tells me that the corrosion rate is not very high (they ship methanol in steel containers), but its not a good idea to store fuel from a vehicle for a long time in any system.  Methanol is worse than gas, not only from the corrosion standpoint, but from the water absorption - water in the system will rust steel, even if the methanol didn't.  That's why some people recommend draining the system as soon as you're done with it.  

If you really needed a way to avoid draining the system you could investigate a plastic coating that would stop the corrosion in the fuel tank.  The injector system would need to be drained however, unless you used corrosion resistant materials (stainless is OK).  There are corrosion inhibitors that will slow this process down to something negligible, but it will cost you additional money.