My coolant tempature keeps on rising while in idle.

Make sure the coolant fan is coming on and the engine coolant temperature sensor is functioning properly .

Check for bad temp sensor

Could be that the thermostat has packed up...

Check all your coolant levels are correct and then take her for a good run out....keep your eyes on the temperature gauge,,if your temp gauge hardly moves then your thermostat is at fault....replace it.

If temp gauge works fine, you may be airlocked in your heater matrix... Try setting heater to full heat with fan on full power,, whilst car is ticking over, remove radiator / expansion bottle cap carefully and start squeezing your coolant pipes. This should force any air out through your rad/bottle top..

Please be aware that as your temperature rises in the engine. Your coolant will expand and start to flow out of the rad/expansion bottle..at this stage quickly replace the cap....check your heater...leave engine to cool....unscrew rad/bottle cap, check coolant levels, top up if necessary and squeeze pipes again..start car with heater/fan on full and repeat above.....

Hope this helps..

Check the coolant level, add some if needed. If you never bled the air out or flushed the system with new coolant, that would be wise to do. Air pockets in your coolant tank can cause pressure and Temps to rise. Make sure your fans are kicking on, once your car reaches a certain temp, it hits a temp switch telling the fan to kick on. Could be faulty coolant temperature sensor as well

Have you checked your cooling fan to see if it is working propely? Let the car idle and get warm and listen for the fan to kick in (if they are electric) or just watch to see if the fan starts to spin faster if it is the old school type with a clutch. Have you replaced the thermostat? A bad one will let the temp rise since it opens too late and then the temp will drop off. But it won't due this only at a light and it will do it infrequently.

Is the engine actually cooling off? If the temp switch isn't seeing a drop in temperature, it will keep the fan running.

When the radiator fans stop functioning properly, the engine temperature will rise as there will be insufficient airflow to cool the radiator. The spike in temperature will be the highest when the vehicle is idling at a stop light or just stopped, but should subside once the vehicle begins moving again.
get the fan cked out.

The coolant temperature should rise until the gauge indicated roughly half. if it continues to go until it reaches the red "H" shut the vehicle off and wait for the car to cool off. The most likely cause of this is the thermostat. It is a $4-$10 part and usually is easy to change. Thanks for asking!

When your temperature gauge reaches "H' it may too late to prevent a major breakdown. Knowing the symptoms of an overheated car and how they occur may be the difference between being inconvenienced and incapacitated.
Identification:---Other than a low oil level or low oil pressure light, there is not a more significant part of a car's instrumentation than a rising temperature gauge or a glowing "Hot" light. These lights are really the only confirmation a driver has that his car is really overheating. It is the identification of the symptoms of an overheating car that enable the motorist to avert a badly damaged engine. Overheating is always a traumatic event for a car's engine, which makes the early identification of the symptom an important addition to the informed motorist's tool kit.
Stuck Thermostat:--The car's thermostat is a valve that controls coolant flow from the engine block to the radiator. When the engine is cold the thermostat remains closed so that the coolant can reach operating temperature quicker and also provide heat to the passenger's compartment. The thermostat has a spring on it that moves depending on coolant temperature causing the thermostat to open. Sometimes the thermostat fails to open thus restricting coolant flow to the radiator where it would be cooled down. This condition is often the cause of overheating. The symptoms of this cause would be a rising temperature gauge and possibly the loss of heat inside the car.
Restricted Radiator:---A car's radiator will have thousands of gallons of coolant passing through in its lifetime. Along with the coolant comes particulate matter in the form of corrosion breaking loose from various parts of the car's cooling system. These contaminates collect in the tubes of the radiator reducing its efficiency. Extensive "plugging" in the radiator will cause the car to overheat. The symptom of this condition would be a rising temperature gauge which goes up when you accelerate.
Coolant Loss:--A car's cooling system is a closed loop system. You are not supposed to lose coolant. Sufficient coolant loss will cause the engine to run hot because engine is heating less coolant to higher temperatures. The symptom of overheating induced by coolant loss would be a pool of coolant on the pavement when the leak is external. Steam under the hood as the lost coolant hits hot parts of the engine, or a rising temperature gauge in the case of a undetectable engine related leak. Of course, the gauge would also go up if the leaks were not detected. Deteriorated Water Pump:--Cars use a belt driven pump to push the water and coolant mixture through the cooling system. This part is called the water pump. Rarely the impeller that draws the coolant through the pump will rust away making it impossible to push any through the system. If this occurs the temperature gauge will climb and coolant will boil over in the radiator. Inoperable Fan:----Most cooling fans are electrically driven. Some are driven by fan belts. If a belt breaks or the electric supply to the fan is interrupted overheating may result. Electric fans are tuned on thermostatically when needed. When the car runs at idle for extended periods or the weather is extremely hot, a failed fan will cause overheating otherwise it serves as a standby assist to the rest of the cooling system. In stress conditions an inoperable fan will cause the temperature gauge to rise. This will help. Thanks please keep updated.please please do rate the solution positively .thank you for using fixya

The next thing to do is to observe the car as it idles for 10 minutes to ensure the electric radiator fan is coming on if not replace the fan relay if that doesn't work replace the coolant temp. sensor that activates the relay that activates the fan after that ti can only be the fan itself that is if the fan is not coming on.