fix or replace

My xj blew a head gasket after 220000 miles. It over heated and now it runs bad. I pulled the plugs and number 6 was soaked with coolant. After it warms up it smoothes out and runs like normal. Should I replace the head gasket or replace the whole motor for a lower milage one? 88 4.0

If you decide to just change the head gasket, you should take the head off and have it checked by a shop for cracks and warpage.

Kinda depends on how much cash ya got layin around. If I were you, I'd take advantage of still havin a good block and buy a rebuild kit. I wasn't so fortunate when I overheated my 4oh. Number five cylinder went sideways on me and completely f'd up the cylinder wall. I coulda re-sleeved but that's hardly worth the money seeing as how you can get a rebuilt long-block for like $1600. Also, since you'd already be buyin a new crank, etc. if you wanted to stroke it it wouldn't be hard at all. Clifford sells a really nice rebuild kit for $800 that comes with cast aluminum pistons, a hot cam, ARP bolts and I believe it comes with a double roller timing chain. And you can get a set of balanced rods for $200. So you'd have a new motor for about a grand

My deciding factors for a motor are the size of the ridge on the cylinder walls, there is only so much you can do with a hone. The amount of wear on the main and connecting rod bearings and races, if they are scored, excessively worn or have worn at an angle (cone shaped). Whether the valve guides need to be done and what shape the valve seats are in.
There comes a point when a motor just isn't worth it anymore.
The head gasket is no big deal (usually), cleaning it up is often the hardest part.

At 220K, you probably want to re-build the engine rather than just the head gasket. Rings, bearings etc probably have some more life in them but why not do it all at once and have a brand-new engine?
Perfect opportunity to build a stroker - 4.5 or 4.6 depending on whether you need to bore it. Crank & rods from the junkyard, rebuild kit from (whoever)... 1/8 more displacement. Voila!