Suspect headgasket.
Do the el cheap headgasket test.
Fill antifreeze to the brim on recovery tank (leave cap off). Remove all spark plug wires. Remove all but one spark plug and have someone crank the engine. If the antifreeze bubbles over, there is leak from that portion of the engine (or cylinder). If not, go to the next cylinder, and then the next.... Note, it could be more than one area or more than one cylinder.
