My car runs fine everythiing seems good, just had a new radiator put on it, but when my car sits running for awhile it starts to overheat, then i start to drive and it cools back down?. please help

The problem possibly could be due to a hole in the coolant system, i.e. a hole in a radiator hose or even the radiator. Loss of coolant will cause the heater to stop working and the engine to overheat. If it runs normally for a time, such as several days or a few weeks, and only after that time has passed the heater stops working and the engine starts overheating, then suspect a leak someplace. If it starts overheating after driving 5 to 10 minutes regardless of how recently antifreeze was added then, possibly the thermostat. It is staying stuck shut and preventing the hot coolant from leaving the engine and cooling in the radiator. The radiator overflow will probably have antifreeze pushing out the cover as a clue. However this can also be the result of a blown head gasket. As far as the fan, does the vehicle have an electric fan or is it driven directly by the drive belt. If it's electric, then warm it up to operating temp and open the hood and listen if the fan runs or not. It will start and stop depending on how warm the engine antifreeze is. If it does run, then the fan is fine, if not then the temp sensor that activates it is not working and needs to be replaced, or the plug into the fan may have become disconnected. If it's driven by the drive belt, then it should not be an issue unless the belt is broken, which would probably be affecting the power steering and alternator as well. If the vehicle has no power steering and the alternator light is on when running and it overheats, check to see if the drive belt is broken/missing. Check also to see if the water pump pulley is wobbly or loose. That would indicate a bad pump and would need to be replaced. Hopefully you just have a hole in a hose, and a simple hose replacement will fix it. incidentally, it's a good idea to replace both upper and lower radiator hoses at the same time, and the upper radiator hose is usually attached to the thermostat housing, so replace the thermostat at the same time too. Good luck.

take the center part of the thermostat out and see if that fixes the problem

may be you should make a diagnostic and you can do it in a garage or you can do it by yourself if you want to do it by yourself you need some tools and you can find some good ones here: diyobd2.fr

My first guess would be the cooling system has some air in it from the radiator job, or the thermostat may be sticking.
You say it is loosing coolant, so you are putting coolant in every day or week ? Is it loosing it on the ground when it overheats ?
If you are adding coolant but not seeing it boil over, it could be burning it and you would not see smoke from the exhaust.

I had a similar problem. Nissan sr18di engine. car would run fine and randomly engine would cut off and only start after 20 minutes. Changed distributer
fine since

Have you checked the crank sensor? They are a common problem item on Jeep vehicles.

You have gone through a lot of trouble so far replacing parts. I wouldn't rely on rad additives for a fix sometimes they do more harm than good. You could just have an air lock in the coolant system. Did you try running the vehicle without the rad cap for awhile to release any air locks that may have occurred? Have you tried a new rad cap? Hopefully this advise helps you some what.

you may have a thermostat going bad, water pump getting weak, or air trapped in the system somewhere. Try to see if there is one or more things that seem to always be present when this happens: sitting still, running air, short trips, long trips etc.

My 98 Jimmy runs on synthetic oil and starts well after sitting in cold weather. If the weather is the problem, try checking that. If it is warm... sorry no ideas.

it sounds like your radiator fan is not working. once your engine reaches a certan temp. the fan should come on to cool it down. also might be the thermostat is not opening. it is not good for the motor at all to over heat and stall. you could ruin your engine. i would change thermostat first and then run it till it starts getting hot to see if the fan kicks on. if it doesn't, it could be the coolant sensor or the fan itself. good luck.