If the cap is bad it could overheat because it will not allow the pressure to build, A new cap is $5 or $6, just replace it. If the hose is not "firm", your water pump may be bad, which means the water is not being cooled, again overheating. With the cap off and the motor cool, so you don't get scalded by the fluid. Fill the radiator up to near the top, Start the car, leave the cap off temporarily, rev the motor and see if the fluid level drops in the radiator neck. If it does the pump is probably fine. If not the pump is probably bad. If the radiator is original it could benefit from an internal and external flush. As over time sediments can clog the rows, restricting them and could cause overheating. Make sure the front of the radiator is not blocked by debris as well. Replacing the radiator is not to bad, a new one can be bought for $100+ shipping. The hardest part is removing the trans cooler lines as they're usually on there very tight and the clips are hard to get to to release the hose. B) Does the electric fan come on? It has a sensor in the bottom right corner of the radiator, when facing the front of the car, that may need to be cleaned or replaced. I replaced my water pump at the 90,000 service along with the timing belt and thermostat. At about 100,000 miles my radiator top plastic tank cracked, so I replaced it and all the hoses and installed T-Bolt clamps on all the new hoses. So my cooling system is like new. I've heard of several others radiators splitting around the same mileage, so plan on doing it in the near future. I have a new pump if yours is bad, let me know if you need it. If the engine starts to overheat while your driving turn the heat all the way up and the fan on low, of couse this will only help cool the motor if the water pump is working. How many miles are on the car?