I have 03 Pt cruiser and I have Overheating problem. Have changed the cap, the t-stat, and replaced the fan (probably the reason for this), Flushed with a flush cleaner mix. the bottom hose is cool but fluid is backing up into the overflow. Please help. It does make that squealing noise how can i tell if the water pump is gone. Don't think I can do that.

After replacing all you have, you're probably going to have to delve a little deeper, mechanically. Had the same problem and it turned out to be a bad water pump and head gasket. I had the problem diagnosed the same at three different shops just to ensure the expense would be justified. Had the work done along with replacing the timing belt since it's recommended at 100K. While the belt replacement has nothing to do with the cooling system, it saved my the money of opening the motor back up and being charged more than having it done at the same time the water pump, head gasket, and thermostat were replaced. Haven't had any problems since. While I am sorry to have to make this expensive suggestion, I hope it steers you in the right direction for resolving your problems.