* Clogged Heater Core: The most likely culprit. Over time, debris and rust can clog the heater core's internal passages, restricting or completely blocking the flow of hot coolant. This means the coolant is getting to the core, heating it up, but can't circulate properly to transfer heat to the air.
* Air in the Cooling System: Air pockets trapped in the cooling system can prevent proper coolant circulation through the heater core. This is less likely if the hose *to* the heater core is hot, but still possible if the blockage is after that point, within the core itself.
* Faulty Blend Door: The blend door controls the mix of hot and cold air. If it's stuck in the cold position, you won't get any hot air even if the heater core is working. You'll usually hear a motor running when you adjust the temperature control; if you don't hear anything, or it makes strange noises, this could be the issue. These are notorious for breaking in Wranglers.
* Weak Water Pump: A weak water pump might not circulate coolant sufficiently, especially to areas furthest away like the heater core. However, if the hose *to* the core is hot, this is less likely.
* Restricted Coolant Flow: Something might be partially blocking the coolant flow *after* the hose you've checked – maybe further along the heater core lines or within the core itself.
Troubleshooting Steps:
1. Check Coolant Level: Ensure your coolant level is correct. Low coolant will obviously prevent proper heating.
2. Feel the Hose Going *Out* of the Heater Core: If the hose going *into* the heater core is hot, but the hose *coming out* is significantly cooler, this strongly suggests a clogged heater core.
3. Check for Air in the System: Look for signs of air bubbles in the coolant reservoir. If you have a pressure testing cap you can use that to verify. This requires bleeding the cooling system which varies somewhat depending on your engine.
4. Test the Blend Door: Try switching the temperature control back and forth. Listen carefully for the blend door motor operating; if there's no sound or it sounds unusual, the blend door or motor might be faulty.
5. Flush the Cooling System: If you suspect a clogged heater core, you might try flushing the cooling system with a coolant flush solution. This is a less invasive option than replacement, but it's not guaranteed to solve the problem if the core is severely clogged.
If the above steps don't resolve the issue, it's highly probable that you need a new heater core. This is a fairly involved job, often requiring partial dashboard disassembly. Consider taking it to a mechanic if you are not comfortable with auto repair.
