Radiator hose issue. Warning Lengthy description
 

So a brief history on the cooling system of this car while it's been in our (this is my gf's car) possession. My girlfriend bought this 91 vert from a guy in Tennessee. It had a radiator/upper hose leak. The original radiator was shot, so it was replaced along with new hoses, year and half later we take it on a 6hr drive to Atlanta to IA a few weeks ago and when we crossed over mt eagle, got a low coolant light. Stopped and opened the hood. Collapsed upper hose. Figured the mountain grade had something to do with it. Let it cool down. It expanded back out, radiator fluid level was good. Got to Dalton Georgia, and thermostat stuck shut. Changed it in a Bojangles parkinglot. Everything was well for next two days in Atlanta. On the way back home. 4hrs in. Had add coolant light go off after we stopped for fuel.(on restart after fueling). Again collapsed hose. This time we added roughly half gallon of coolant. 4days later heater core hoses(someone rigged the heater box, will post pictures later) and hose burst. Sourced a new to me heater box, and new heater core. Refilled the system, burped all the air out of it(that I'm aware of) out and now every time it is shut off, the hose collapses. We have a pressure relief style cap, and if you flip the lever it expands back out and radiator coolant level is full. Expansion tank has fluid in it. What am I missing/or doing wrong here????

Sounds like there could be an internal seal leaking water into the rotor housing. This will cause low coolant. I'm guess the hose collapse is a symptom of the engine pulling a vacuum on the cooling system via the bad seal. This is all purely speculation.

Thanks. The car has never over heated during all of this. Not according to the guage anyway.

This is common if the radiator cap is faulty, or if the hose from the radiator to the recovery tank is clogged. Clear out the hose and install a new cap.

ditch that "pressure style cap with relief lever".
Get an OEM cap and see what happens.

It was the cap. Thanks guys. Cooling system works as it should.... For now. Now on to the massive things wrong to try and fix with this car.

Situation has deepened. Car has been pulled off the road
 

The collapsing hose issue has now changed from doing it after cool down to now roughly 100 miles into a drive low coolant buzzer goes off. Car does NOT overheat according to the gauge. She pulled over after buzzer went off. Shut car off. Hose was collapsed and puking coolant out of the overflow. After it cooled down enough to touch the cap once we opened it, hose opens back up and coolant almost returns to normal. So I believe it's a seal failure. Car is now being pulled off the road. I will pull the engine apart and rebuild it after we finish the 2.3 st swap in the girlfriend's other car so she has something to drive again.