I'm no chemist but wouldn't some specific gravity device (hygrometer?)
The drag racers use a hygrometer to determine the ratio of nitro to alcohol, but with oil and several differant weights of oils its impossible to tell with a hygrometer.
Not sure I understand your test, but methanol is used as a gas deicer as well as a windshield washer antifreeze. That is it will mix with water and prevent the water from freezing.