1990 7.3 n/a 5spd 4x4 180k miles Correct Motorcraft thermostat, installed about a year ago. BB check valve in place. Clack clack. New Carquest water pump 2k miles ago, no leaks. Confirmed lower rad hose has spring intact. Confirmed upper rad hose is compressible. New 13psi radiator cap. Non lever locking style. Hose into overflow tank is good. No cracks in overflow tank, No leaks. Truck is stock fuel & stock timing. Can shine a flashlight through radiator, doesn’t appear to be clogged up externally. Looking under truck and around heads, no signs of cracks or coolant loss. Oil level is good, and no signs of coolant. Coolant is a little cloudy, but no signs or swirl or oil presence. Personally, I’ve never heard the fan clutch engage with the roar people explain. Shouldn’t be an issue when traveling 50-60mph though. Regardless, will be cleaning the bimetal coil and adding some silicone RC fluid to the housing to see if it makes a difference. Have tested the factory temp gauge by grounding out the wire. I also have a Bosch gauge on the pillar that is plumbed in at the factory location for the over temp sensor light. Towing about 8000 lbs up some decent grades in PA last week, it got hot. Highest was 240-245F, with outside air temps around 75. At the top of the climb, I pulled over, popped the hood, and let her idle. Came back down to around 210-215 within a few minutes of idling. At what temp do these things pop gaskets? If over temp light is set to come on at 242F, I was right in that zone for sure. Don’t really see much of a bleeder port for air burping. Truck used to tow this same route much cooler, old water pump bearing went out and starting dumping fluid (locally, not while towing), put on the new wp, New green coolant/distilled, SCAs, and last week was the first real long haul towing I’ve done since this work. Just fired it up cold with radiator cap on, and after idling 30-40 seconds there is a good amount of pressure when I loosen the cap. Idling at 190F and cap on, I don’t see any bubbles in the overflow tank from the black hose. Has some white smoke at startup when cold. Doesn’t smell sweet like coolant burning, but could just be masked by the cold diesel haze. The pics are driving it yesterday in 85-90F outside air temp, AC on, unloaded, 5th gear on a mild hill climb @65mph. Shouldn’t be getting to 215F unloaded, seems high when thermostat should be wide open @ 192F and also combined with interstate speed airflow across the rad. Bad head gasket? Exhaust gases pressurizing the cooling system? Air pockets? Anything else to check before I order a gasket kit and tear it down? Was planning a 12v swap in the spring and was going to gather parts this winter. Would really hate to sink the time and money into this ol boat Anchor. Great engine, just no power and mediocre mpg. Thanks!