For some reason my coolant temperature gauge rises to 119 degrees celsius when driving then drops back to 100 celsius but rarely if ever stays at the normal 82 celsius operating temperature. Yet, I have replaced the radiator, water pump, thermostat, thermostat housing, thermometer, and fan clutch. The hoses attached to the radiator are good condition. The thermostat was checked before in hot water to ensure that is was not defective.
Additionally, my mechanic has an infrared laser and simply points it at any engine part and measures the temperature. We pointed the laser directly at the thermostat housing and thermometer which sits about a centimeter away and the infrared beam reads perfect 80 to 82 celsius. The radiator reads the same. But even while idle the gauge reads over 105 celsius. Now, I just had the head gaskets replaced and 9 valves replaced and after putting the engine back to together the black plastic covering over the center of the straight 6 engine does not screw back properly because the threads inside the head are stripped. The cover comes up about a half an inch when the hood is raised but is kept in place by the plastic air intake that goes over the top of the engine. Any advice would be appreciated...