NotAImportGuy

I have a 91 honda accord ex coupe, I have replaced the radiator cap, thermostat and have flushed the system with blue devil radiator flush from AutoZone, I still get hot and sometimes over heat, I don't loose coolant and I don't build alot of pressure in my cooling system, I have done the head gasket test hooking a coolant pressure gauge to my radiator checking for air being forced into the cooling system, I don't loose coolant, coolant seems to flow, fine hooking a hose to the inlet of the radiator hooking a hose to the inlet of the engine, I have been told it could be a bad water pump or a blockage some were in the cooling system die to the fact it stays at a consistent temp while idling don't increase or decrease, and anywhere from 3k rpm and up going down the road don't matter what gear your in temp stays down but soon as you drop rpm and cruise it gets close to over heating or does over heat, fans work and everything just lack of coolant flow is my assumption, I have let the car run no rad cap for over a hour hoping for a air bubble have got nothing out of it, heater stays on all the way full time, to help keep cool, any ideas? Hoping to get a answer before dumping money into parts that don't need to be replaced...