My heat is not working that good. When it gets colder outside and my car's temp gauge goes down, the less heat I seem to get out of the system. When the car is idling at a stop is when the heat starts working good. Any ideas what this problem is?

If it is a manual system--sounds like coolant low ie: air bubble in system. If it is ATC system, Check Codes, if no failure codes, coolant may be low--air bubble in system--most Durango's have air bleeders in system.

The car will run richer in cold weather, especially at start. You may have an exhaust leak. Put something over the tail pipe and listen for hissing under the car. Any hiss is an exhaust leak, must be fixed.
The gauge thing may be an old, loose alternator belt, giving low voltage when things are cold and stiff. A new belt may help. Do a voltage check while watching the gauges..

the way to check the thermostat is with the motor hot feel the upper radiator hose to see if can squeeze it. you should be able to squeeze it. the water pumps is big problem to

year??????

What is the temp.gauge in the vehicle say. You might try a new thermostat 1st if it is reading low as this is where the heat comes from.

First check your antifreeze level - especially if your car is equipped with the 3.4L engine. these are known for coolant leaks due to failed intake manifold gaskets. Coolant levels that are slightly low can cause poor circulation through the heater core and can "fool" your gauge sending unit into "thinking" that the temp is low when the engine is actually on the verge of overheating.

If the coolant level is OK when you check it, replace the thermostat.

Check the air cabin filter located outside under the vent where the wipers are. Should be the passenger side. Probably dirty.

change the thermostat and the temp gauge in the radiator

You have air in the cooling system, it needs bleeding, this is best done from the heater hoses. you cannot have a heating or cooling sysem that is not pressurised. no water no heater no demister no temp guage

should be fine as long as the gage goes up and down and you get heat it should be fine make sure you consider the outside temp. as the engine starts it will heat up get really hot the the thermostate opens and the gage will fall and should but not always stay low it could just be the ip gage.