How many miles can a person put on a 1999 Ford Escort LX Sedan until the car should be replaced?

Depends on many things. A couple hundred thousand miles should be seen by the majority of the cars. They get replaced when it costs more to repair than what they are worth.

As a technician in a niche market I have often had long commutes: averaging about 100 miles a day, about 50 miles a day on weekends, that 31200 miles a year. Needless to say I go through a lot of cars, around 1248000 miles worth. Of the 5 ford Escorts (1.9L) I have owned I loaned one to a good friend and he said it made it to 202k miles. I never saw one make it past 180k miles. Do not get me wrong they are good cars for what they are. I like to pick them up at about 70 k miles for around $700 then fix them my self, that why I can get them cheap. The parts have cost me about $300 on average. If you are have a mechanic fix it you can make that around $1200, just buy a newer car. So it comes down to about $1000 to drive 110 k miles, not to bad. I would not bother with a replacement engine, even today buying them on the Internet you just can not be sure of the miles on the engine. Also you have the cost of installation, around $900 total. As for rebuilding the engine OK if you do it your self other wise it cost more that the car. Most good shops do not want to get involved in a a job that cost more than the car is worth, especially on a car used for commuting.

I just got my 1997 Ford Escort lx sedan 2.0L and it's sitting at 318,000 miles original engine and tranny