New to forums and new to mechanics I suppose I am a carpenter but I just bought a new work van it is a 97 e-250 everything looks good 170k miles but when you start it, white smoke comes from the exhaust but dissipates. once it is warm the oil pressure drops to nothing and it struggles climbing any Hill. I just replace the oil and filter and put in 15w40 and that seemed to help a little. I have read up on this 4.2 liter especially the 97 and haven't come across good things any knowledge would be much appreciated plan on taking it in this week to get fixed but would like to make sure what the problem is prior would it be a whole engine rebuild or just gaskets?

 

170,000 mi isn't exactly rebuild time, but the drop in oil pressure is something to be concerned about.
What you might consider would be a thorough check out including a compression check.
If routine service was stretched and possibly ignored, 170,000 is getting close for some major work. I would also suggest to have someone check the actual oil pressure with a reliable gauge to confirm there is an engine wear problem. Dash gauges are usually not that accurate and can sometime provide faulty readings.
If low oil pressure is confirmed, sometimes it is cheaper to replace the engine with another with just less miles and less wear. That decision will depend on what the tests reveal.