If your donuts taste or feel oily, you may have put them in before the oil heated up to 350℉/177℃. To guarantee your dough doesn't absorb the oil when cooking, make sure your oil is at the right temperature before you add them to the pan. Another common issue is overcrowding the pan, which can lower the oil temperature too. Frying a few donuts at a time without crowding the pan will deliver better donuts.