uniacke-hatch

So I've had the cooling system looked at three times. FYI 95 Civic CX Hatchback 1.5. Nobody can tell me why I'm losing fluid. But I can tell ya this. I drove 1200kms yesterday. At km 400ish my temp guage started to rise. My cooling fan is on 100 percent of the time by the way. But she never really went really high. So at km 650ish I went for a hike so the rad could cool so I can check it. So when I got back to the car the tubes were all collapsed. From end to end. I took off the rad cap and there was negative pressure and I poured half a litre of fluid in her. Oh, and the resovoire was full to the top. I got home last night at km 1200ish. This morning I checked the rad and the fluid was down and the tubes were collaped and the resivoire was full. Again. So, Is the rad cap letting fluid out into the resovoire but not back in? and the resivoire must be leaking the fluid through the cap cause it can't handle all that fluid and is not pressurized. I'm told the tubes shold not collapse either. Should I replace the rad cap and tubes? Any other suggestions. I'm getting tires of carrying pre mixed antifreeze everywhere I go.