Situation: Engine overheats when at full stop or speeds less than 50mph. Also begins to overheat when driving 45+ consecutive highway miles at speed limit.
Repairs so far: Water pump, timing belt, and thermostat replaced at 147,000 miles. Radiator replaced at 156,500 miles. Coolant is new Genuine Honda coolant. Automatic Transmission rebuilt at 123,000 miles.
Observations: At low speeds or at standstill, I can turn the heater dial to " Hot" and only get warm air, not hot. Hot air is only available when driving at 50mph+. I can pinch the upper radiator hose, then release it and feel the gush of coolant flow when the engine is running at normal temperature. There are no leaks/damage to the upper/lower radiator hoses. No visible sign of leakage where the radiator cap sits. I do see some leakage from the reservoir cap area despite a properly sealed cap. The overflow bottle appears to fill up beyond the Max level on its own when the engine is running hot. The transmission begins to shift harshly as the engine overheats. No coolant is present in the tranny fluid or vice versa. Both fans come on when the engine idles or when going up steep grades.
Suggestions: Do I have air trapped in my coolant line? Need a new radiator cap? A blown head gasket? Cracked cylinder block? I don't see any visible leakage coming from the engine block or any lines that carry coolant. I'd appreciate your help. Thanks!