I made biodiesel using ethanol and sodium hydroxide. On the first day, the amount of catalyst was tried 0.6-0.8 and 1.0 gr, respectively, and glycerol precipitated. On the second day, the amount of catalyst was tested 0.7 and 0.9 g respectively and no glycerol precipitate was observed. I didn't understand why these interim values.
I made ethyl biodiesel using 99.5% anhydrous ethanol, it worked in the regular manner as with dry methanol. When I tried making ethyl as opposed to methyl ester biodiesel using caustic dissolved in the 95% alcohol + 5% water , I got no reaction. If too much water is in the alcohol the normal transesterification reaction does not proceed.
Water in the reaction from any source can stop the reaction and cause soap rather than biodiesel being produced. I removed a sizeable percentage of water from inexpensive lye, drain cleaner, sodium hydroxide, by heating it maybe 200 degrees centigrade , under about 100 millimeters of vacuum pressure. There might be water in your oil. A simple test is a hot metal pan test. Heat the pan to maybe 140-150 degrees centigrade, not enough to burn, decompose the oil, then put some drops of the oil on the hot metal and see if water boils out of the oil. Compare it to unused store bought new oil, in a hot pan test.