* Blocked Heater Core Inlet/Outlet Valves: Many vehicles have valves that control coolant flow to the heater core. These can become stuck closed due to corrosion, debris, or internal mechanical failure. This is a common culprit.
* Obstructed Heater Hoses: While you mentioned obstructions, it's important to check *all* hoses leading to and from the heater core. Kinks, collapses, or internal clogs can restrict or completely stop flow. These hoses are often hard to see and access, requiring some disassembly.
* Faulty Water Pump: The water pump is responsible for circulating coolant throughout the entire system. A failing water pump, due to wear or a seized impeller, won't circulate coolant effectively, impacting the heater core's flow.
* Air in the System: Air trapped within the cooling system can prevent proper coolant circulation. This air often collects in the heater core's higher position. Bleeding the cooling system (removing trapped air) is a common solution.
* Thermostat Issues: A stuck-closed thermostat will prevent coolant from circulating throughout the entire system, including the heater core. A stuck-open thermostat is less likely to cause this specific problem, but it could still contribute if flow is already restricted elsewhere.
* Low Coolant Level: Insufficient coolant in the system obviously reduces the volume available for circulation, impacting the heater core's flow.
* Clogged Radiator: A severely clogged radiator restricts overall coolant flow, potentially starving the heater core.
Troubleshooting Steps (in order of easiest to most difficult):
1. Check Coolant Level: Ensure the coolant reservoir is filled to the proper level.
2. Check Heater Control Valves: Locate the heater control valves (often near the firewall) and see if they're operating correctly. Try switching the heater control to "hot" and feel for movement or resistance. This is often the most accessible first step.
3. Inspect Heater Hoses: Carefully examine the hoses leading to and from the heater core. Feel for blockages, kinks, or softness indicating a potential collapse.
4. Bleed the Cooling System: Look up the procedure for bleeding the cooling system on a 2000 Elantra. This usually involves opening bleed valves (if present) or carefully removing air pockets by running the engine and manipulating the heater control.
5. Check Water Pump: Inspect the water pump visually for any obvious issues. A running engine often makes this difficult, but you can listen for unusual noises. A mechanic can easily check water pump function.
6. Check Thermostat: Replacing a thermostat is relatively inexpensive and can solve a multitude of cooling system issues. This would typically be performed by a mechanic unless you are very mechanically inclined.
7. Radiator Inspection: Flush the radiator and inspect it for internal blockages if you suspect this is the issue.
If you're not comfortable performing these checks yourself, it's best to take your Elantra to a qualified mechanic for diagnosis and repair. They have the tools and expertise to pinpoint the exact cause efficiently.
