Hello, I have a 99 expedition with the 4.6 and almost 170,000 miles. As far as the engines, there is the 4.6 and 5.4 They are both smooth running motors and will last you plenty long enough with proper maintenance. If you have a choice between the 2, I would lean towards a 5.4. Not only for the extra power, but most expeditions with the 5.4 have a bigger trans and rear axle. I have had my rear axle go out, but other than that, no big problems, she purrs like a kitten. The 5.4 is a very good motor, but due to the new aluminum heads, they have been known to give problems when replacing the spark plugs. The first year 5.4s are known to blow out the spark plug when replaced, but there is a company that makes replacement threads for this, and is not a very hard fix. I would not let this scare you off, because other than that possibility, Expeditions are very reliable vehicles.