My Jeep overheats while sitting idle. When I drive, the gauge goes down quickly. I have had thermostat and fan changed. I have also had the radiator flushed. What can it be?

Over heating the engine is a serious concern. With the hood raised you should hear the motorized fan turn on just behind the radiator as the engine requires additional cooling.. If you look in from the rear of the radiator you should see the fan blades.

This electric powered motor operates on a thermostat and when the engine temperature rises this fan should come on. I'm assuming from your description that when driving and air is flowing through the radiator as the car travels the engine is nor overheating.

Check fan motor thermostat, check fan motor and check wiring.

Wiring Diagrams related to the Honda Civic
http://www.wiringdiagrams21.com/category/automotive/honda-automotive/civic

Motor engine cooling fan only runs as engine temperature requires additional cooling.

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

Well, yes and no.
The shroud helps the fan pull more air thru the radiator.
So yes the broken shroud could be a factor, but you could also have problems with air flow thru the radiator. Or restrictions inside the radiator for coolant flow.

At idling speed an engine does build up a lot of heat and the cooling fan will kick in. In slow moving traffic or traffic jams the temperature gauge can touch the red - particularly on hot days. The reason it cools down when you start moving is because of the air flow through the radiator.

Presumably there are no leaks from the cooling system otherwise you would have mentioned it. In normal circumstances the fan will not be running as you are driving at speed, as the air-flow through the radiator is sufficient to cool things. The fan only kicks in to get rid of excess heat - and this usually occurs at idling speed or after you have parked the car.

If the fan is running all the time as you drive, this points to either a fault in the fan switch, or the car is running too hot. presumably in normal driving the fan isn't running and the temperature gauge reads normal?

It is common - in stationary traffic many cars overheat (particularly big engined models) try to stall and 'cut out'. Restarting can be difficult until the engine cools down.

Is your car overheating in normal driving conditions or just at idle speed? Overheating in normal driving conditions can be caused by things like a failing water pump, blocked radiator, collapsed hose, faulty thermostat or, in the worst case scenario, cylinder head problems.

Overheating at idling speed is 'common'. Check your coolant level. If your car isn't using/losing coolant then there probably is no major problem. You can flush out the cooling system and refill with new coolant - and also check your radiator. Are the cooling fins crumbling with age? Or maybe they're partly clogged with insects and debris from the road? A blast with a hosepipe wil sort that out ..

The question is how much does your car overheat in normal driving? If it doesn't .. it appears as though you have nothing to worry about as such. Most cars have 2 speed fans... the 2nd faster stage kicks in at some point dependant on engine temperature. Perfectly normal.

does it overheat going down the road if not check to see if radiator fan(s) is running when it heats up at idle car needs fan to run cool at idle but not while going down road

It could be either.Replace the thermostat anyway for good measure (it's cheap).And have the fan and relay tested.I't a very easy quick test that any honest,capable machanic can do

This might help you as it looks as though you have an electric fan to cool , there should be a sensor on your radiator hoses upper and lower.they are actually switches triggered by the coolant temperature in side the hose. While your Jeep is sitting idle, shut off the AC as it adds to the heat off the engine not to merntion useing more gas. you should make sure both high and low speeds on the coolant fan work. good luck if this does'nt help check out the post, with more, on the 1995 Jeep heating up..

Check to see if the electric radiator fan works, run the car and turn on the a/c on high to see if the radiator fan comes on. If it doesn't come on then check the fuses and relay to the fan and wire harness to the fan. Check the radiator it self, check the out side to make sure the heat exchange finns are not plugged up with winter mud and dirt, and the inside look clean and corroded or plugged with rust.
If that is ok then change the thermostat and the hose, a soft hose will collapse and restrict the flow of antifreeze. The last cause would be a bad water pump and not pushing the antifreeze as much as it should.
Good luck and hope this helps.

Have someone flush cooling system & check condition of rad for debris in front of rad & blow or spray it out as necessary. Next time it runs hot, turn your heater temperature up high, blower fan on high, and see if gauge starts to come back down a little. If it does, my guess is your rad needs replacing, or at least consider trying a good reverse flushing of the system first, then rad.

You will need to Change your Thermostat. A bad Thermostat will cause the Overheat Problem as Stated above. Also, Check you Coolant Level, and see if the Water Pump is Pumping Water through the Radiator. Please Rate my Response, I need all the Help that I can Get! Thanks!