White smoke coming from tail pipe on 2001 ford expedition

You are not going to like this answer. Your engine is burning oil. In all likelihood, you have one or more burned out piston rings, which is allowing oil to get into the combustion chamber. Snce you are burning oil, it is going to eventually foul your spark plugs and reduce performance significantly over time. You will also need to check the oil more frequently to try to avoid running dry and seizing the engine.

At a minimum, you are going to need a ring job. The most common cause of this is going way too long between oil changes, especially on a high mileage vehicle; it is also one of the most avoidable vehicle malfunctions.

Sorry to be the bearer of bad news.