To give some back ground, there was a freeze that lasted a couple of days and froze the water in my radiator solid. The truck didn't have antifreeze, due to a recent heater core replacement, and waiting on a new radiator to correct a leak that had developed. The hoses all froze, causing a crack in the oil cooler, (replaced)...which pushed engine oil into my coolant reservoir, but not into the motor due to plugged hoses filled with ice. Changed the radiator, thermostat, removed and verified hoses were clear of ice, and added coolant. Since the repair, and burping the system, my truck runs slightly hotter than normal (though still below half on the gauge) when idle and up to 65mph or so, then climbs to 3/4 hot and fluctuates radically up and down on the gauge, but never overheats. Pulling over to the side, the temp goes down almost immediately to normal, but there is boil over in the reservoir. I have verified no water in oil, and engine runs as close to normal as i can tell. No codes. Also, I have no heat from heater but the lines going to core are hot. The heater worked fine before, so I am checking the blend door now. Anyone got any ideas on why the overheating?

 

it sounds like a FLOW issue...

water pump., blocked heater core..

a pressure leak.. somewhere..
pressurized system.. water boils at 212,,, and radiator cap is 12-15 psi .. to allow water to go to 250 before boiling.
thermostat is 180 to 200...

also check ALL the freeze plugs in the block and heads.. freezing is very harmful..

 

So its all thawed im guessing...Did the thermostat take a hit? Water pump should be fine.
Time for a new radiator or get it flow tested. Pull off heater hoses and check core for clear.

 

There has been more than one engine ended up with a cracked block/head due to freezing.