I have a 90 cherokee and the other day I was driving it home and it started to hesitate and when I got home it was idling bad so I gave it some gas and it started smoking a greyish white smoke. I turned it off and checked my oil and its still clean. So then I pulled the plugs and the #3 plug has oil on it. It has overheated twice before and I changed the radiator, water pump, t-stat, heater control valve and havent had an issue with temps since then and its ran fine until yesterday. Any ideas?

 

sounds like it could be rings