How do I Fix Water in the Fuel Tank?


Hi John,

Thanks for your radio program.

I was told by a friend that if you occasionally put some methylated spirits into the petrol tank (say half a cup) that it absorbs any water that may have accumulated on the bottom. Do you believe that?




Hi Stanley,

Thank you for listening on Radio 2UE. 

Methylated spirits is sometimes also called denatured alcohol. Basically it is ethanol (the same stuff as in the 'E' in E10 blended petrol and also wine, beer and spirits). However, it also has a small proportion of other chemicals added make it poisonous, and very bad to taste/smell.  This is done to stop people drinking it recreationally.

It is generally used as a solvent and can be used as a fuel for burners and camping stoves. It's a common household solvent. The main additive is about 10 per cent methanol (which is the next most common alcohol - but a deadly poison, which also causes blindness). The use of methanol in the mix gives rise to the term 'methylated' spirits. Methanol is also a common fuel in racing cars, especially drag racers. Other chemicals found in methylated spirits include isopropyl alcohol, acetone, methyl ethyl ketone, methyl isobutyl ketone, and denatonium.

None of these chemical additives alter the ethanol in the mix. They're just there to make it unpalatable, poisonous and undrinkable. They also make it almost impossible to distil the blend to extract the ethanol and drink it subsequently. 

In other words, 'metho' performs like ethanol for basic chemistry purposes.

One of the salient features of alcohol (ethanol/methanol, etc) is that water mixes with it. The chemical term for this is 'miscible'. Water doesn't mix with petrol. But alcohol also is miscible with petrol. So, when you add water, ethanol and petrol, you get a miscible solution of all three liquids. 

In other words, the water dissolves in the alcohol, which itself is dissolved in the petrol. (Industrial chemists prefer to say 'miscible' - but you get the point.

A small amount of metho in the tank, occasionally, can get rid of a very small amount of water trapped down the bottom.

If you have a 50-litre tank, I'd have no hesitation in putting a bottle of metho (call it one litre) in the tank. Effectively, this would be a do-it-yourself E02 blend. That would take care of some moisture trapped in the bottom of the tank.

However, a simpler solution to the problem would just be to fill up occasionally with E10 fuel (provided the car is compatible with that fuel). More ethanol equals more opportunity to dissolve more water and eliminate it by ingesting it into the engine.