Has it been wheeled? Wheel is way harder on an engine than regular driving. I bought my XJ with 185,00 on it. Put about 80,000km as an everday driver. After I began wheeling it it went downhill fast. So I replaced it with a used enigne(90,000kms) on rebuild. Have put maybe 5,000kms on it and now its got a knock, I put the XJ on a steep sidehill, didn't roll but left the engine running to power the winch to pull myself out. I think it may have run a bit dry. :oops:
Any on average I would expect to start seeing problems at 250,000kms on a 4.0 and by 280,000-300,000 it will need replacing. Less if wheeled.