1. Thermostat: This is the most common culprit. A stuck closed thermostat prevents coolant from circulating properly, limiting heat to the heater core.
* Check: Feel the upper radiator hose. If it's cold or only lukewarm when the engine is warmed up, the thermostat is likely stuck closed.
* Solution: Replace the thermostat. It's a relatively inexpensive and easy repair.
2. Heater Core: The heater core is a small radiator inside the vehicle's cabin. If it's clogged, restricted, or leaking internally, it won't heat effectively.
* Check: Look for leaks under the dash on the passenger side (most common location). Check for a sweet smell (antifreeze) in the cabin, indicating a leak. Listen for unusual gurgling sounds from the heater core area when the heat is on.
* Solution: Repair or replace the heater core. This is a more involved repair, often requiring partial dashboard disassembly.
3. Water Pump: A weak or failing water pump won't circulate coolant effectively.
* Check: Listen for unusual noises from the water pump (whining, grinding). Check the upper and lower radiator hoses when the engine is running; if there's a big difference in temperature or pressure, it could suggest poor pump circulation. A visual inspection for leaks is also recommended.
* Solution: Replace the water pump. This is a moderately complex repair.
4. Blend Door Actuator: This part controls the amount of hot and cold air mixed. A faulty blend door actuator might be stuck on the cold setting. This is less likely if you have *no* heat at all, but worth considering if you get some, but not much heat.
* Check: Inspect the blend door actuator mechanism (usually located under the dash). Listen for any clicking or unusual noises when adjusting the temperature controls.
* Solution: Replace the blend door actuator (relatively easy).
5. Low Coolant Level (despite refill): Even with a new coolant fill, you could have a slow leak somewhere in the system. Check for leaks around the radiator, hoses, water pump, and heater core.
* Check: Carefully inspect all coolant lines and connections. Look for wet spots, corrosion, or signs of leakage. Use a pressure tester to check for leaks in the cooling system.
* Solution: Repair any leaks; replace damaged components.
6. Air in the System: Air trapped in the cooling system can hinder proper circulation and reduce heating performance.
* Check: Check if the system is properly bled after the coolant was replaced. This often involves opening a bleed valve at a high point in the system (often near the heater core).
* Solution: Bleed the cooling system according to your vehicle's specifications.
Before starting any repairs:
* Safety First: Allow the engine to cool completely before working on any part of the cooling system. Coolant is hot and under pressure when the engine is running. Wear appropriate safety glasses.
* Consult a Repair Manual: A repair manual specific to your 2000 Dodge Durango will provide detailed instructions and diagrams for all the components and repair procedures.
If you're not comfortable working on your vehicle yourself, it's best to take it to a qualified mechanic for diagnosis and repair. They can quickly pinpoint the problem and fix it efficiently.
