What would have to be done to paint a car that now has oil base paint on it ? The kind that is used on tractors. Would it give any problems when finished with automotive paint? Thanks

Depends, put some of the thinners on the paint see what happens..
It would be far safer to strip and repaint, one can get weird things happening with odd ball paint systems...from frying patches when laying the paint to crazy cracking after the 1st good summer.

Dont do it !!!! strip it off start over nothing good can come from this. please strip it off and coat the car in a good epoxy sealer and start from there

Strip it would be the best option.. However, if you want to see if you can get away with it i suggest you pick a small panel such as the header or something. Sand it a bit with 320 and apply a "barrier" coat of a quality sealer on it to see if it reacts. If it doesnt react you should be good. Another option is a waterborne primer. I have yet to see a waterborne primer react with anything in all my years on refinishing. These options are only if you simply want to get paint on the car. If you are trying to do something quality that will last many many years, strip it.

Strip it, paint is only as good as what you put it over. Not worth the risk, with the cost of good or even decent materials today, not even mentioning the amount of labor that goes into producing a good paint job. I wouldn't leave that junk on there, start fresh with materials that you know will be compatable, and 2k products for a good foundation and long lasting job. Stripping will also give you the opportunity to see what the car has been through all the years of its life, and if any poor repairs were done that should be repaired properly. Some nasty work can be hiding under paint, and if they went so cheap as to use oil based paint on it, I almost expect some surprises to take care of.

Strip it!