Had to change out the control arms.....truck sat for a couple months while slowly did the control arms......did start and run a few times, not for long, during the time the truck sat....
some very cold weather(one of the reasons it took so long).....once job done.....started it up.....let it run while getting it ready for a test drive.....happened to go inside to check something.....
and the temp gauge was pegged.......just then.....coolant steam started spewing........lost a some coolant.....of course shut truck down immediately.......noticed had no heat in the cabin.....

after letting things cool down....restarted.......now temp gauge does not register any temperature......truck engine runs fine.....;no coolant leaks.......and no heat whatsoever in cabin......and
am sure truck begins to overheat again....as fan comes on fairly soon.......coolant level still looks full....but I know some coolant was lost by amount that leaked out on the ground.

My hypothesis......some kind of blockage, maybe in heater core......some how stopped coolant from circulating properly....causing over heat condition(OBD indicated coolant overheat condition)....
which caused too much pressure, causing a coolant hose seal to temporarily fail......??...or possibly water pump failed!!!/combined with a temp sensor failure(gauge doesn't move)???

Truck was fine before....never ran hot......Thanks in advance for any ideas.....

 

You have a leak that is not temporary. Pressure test the system and sit and wait. The leak will show itself. Those hose spring clamps are tough and don’t temporarily let up.

Harbor Freight has a test kit that fits LR3.