I don't know why but Jeeps tend to do that. Water pump is going to go within 6 months if it is not already bad. Cooling system needs to be flushed again in 30 to 60 days as it will already have all the corrosion inhibitors gone and will do it all over again. CHANGE THE THERMOSTAT. Guarantee it is going to fail.
How do I know this? Used to work on Mail Carrier Jeeps.
