1994 Dodge Shadow cooling system&valves

First of all I want to ask if you can help me with a problem that im having, first problem is in the cooling system. What my car is doing is when im driving the tempurature guage goes all the way up to h on the guage and then goes back down to the middle between hot and cold whenen the day is a cool day then on hot days it goes from c to h and stays at h throughout the driving period. What I noticed is that the coolant for some reason keeps backing up into the resovoir, some days I will chck the overflow resovoir and it will be at close to minimum then other days I will check it and the coolant is over the maximum mark on the resovoir and then it spills out of the overflow hose on the resovoir and get all over the engine and the alternator, etc. Wat can be the problem?And my second question is at the top of my engine sits my camshaft, lifters etc, now there is a pronounced clicking coming from under the valve cover, andi dont know what iit is, can you help?Please thanxxxx!