THIS IS IMPORTANT! On later model tractors, you want to carefully and slowly add engine oil at the filler pipe. If you fill with oil too fast, it can cause engine damage. Just don't dump the oil into the filler. Pour it slowly/normally and you'll be fine. If your tractor is not one of the newer models (later than 2005), this doesn't apply, but you didn't say what year your tractor is. It is also more common to happen when people are changing oil and pouring from a gallon oil container instead of quarts.