Saturn Repair: overheating, temp gauge, themostat

Question
replaced the radiator, the fan motor, the fan temp sensor, the themostat, and the engine still seems to run hot. also changed the coolant.  initially the temp gauge ran at less than a quarter of the gauge. now it runs at just above a quarter of the guage to about half. the fan only goes on when the ac is turned on cooling the temp to just above the quarter mark.  strange that while idling with the ac off the coolant will boil over through the coolant bottle.  appreciate any clues as to the problem  and how to correct it. thanks talipp.

Answer
Hi u say it only goes to about 1/2 on the gauge? that is normal also with the cap off the coolant will flow out through the cap for 2 reasons the resevoir is too full or the car is starting to come up to temp .. with a car if there is no cap on it the fan wont come on the fan comes on at 220 so if the system cant be put under pressure it will run out. so if it is running at 1/2 it is normal.. for every pound of pressure u put on the system the boiling point raises 3 degrees so with a good cap u can raise it by 45 degrees thats y the fan will come on with the cap on not off