Things that cause XJs w/closed cooling system to overheat
AIR in the system,closed system is good for this.Burping the system can be done,and if you ask 10 different people,you'll get 10 different ways of doing it.
Bad pressure bottle,usually leaks where the small fitting is on the drivers side.
The newer type bottles have a piece of metal tubing in the fitting I guess to give it strength.
Pressure cap for the pressure bottle,notorious for leaking,also has a rubber o
ring,once it over heats,yor prolly gonna have to replace it.
Backflushing the system.This is fairly easy to do and should be the first thing
that should be done.Also check all hosees and clamps,heater control valve,
Best thing I have done is swap out the closed for the open system,bout $220.
n coulpa hrs driveway time.Did it last yr,hasn't got past 210 yet