My 2004 Honda Civic is losing coolant and overheating. No visible external leaks, no water in oil, runs great, all new hoses, new thermostat, new radiator, water pump fine. It uses about 1 quart of coolant a week. When I shut the engine and even after it completely cools down, there is still pressure on the system. I can hear the pressure escaping when I take the cap off and the hoses are hard. It will not suck coolant back into radiator from reservoir. It has heat but not quite as hot as normal. What do you think?