Just bought 2009 Wrangler JK X, 90K miles. Heat at vents from left to right: 80, 120, 140, 160 on 40 degree day (Fahrenheit).
Both heater hoses measure the same, nice and hot.
Here are the steps taken so far.
1. Verified blend door under steering wheel next to center console is functioning properly.
2. Flushed heater core with 20 gallons of water going both directions through heater hoses, refilled heater hose with antifreeze before reattaching. (no change)
3. Performed coolant system flush using Prestone Radiator flush. Ran 3-4 hours, drained and filled with water, drained again. (no change)
4. Flushed heater core with 20 gallons of water both directions through heater hoses again. (no change)
5. Filled with Mopar coolant and bled system with front wheels on ramps. Filled heater hoses with coolant. (no change)

I have seen some YouTube videos using Muriatic Acid to flush the heater core but solution only worked for about six months. Heater core was replaced and found to have greasy sludge inside. Is there a lasting solution to this problem? Thanks for your help!

 

Welcome to JKF.. Outstanding effort on the issue posted. Have not checked our 13 JKU and I'm not aware of any factory specs for temp on heater output; given that both hoses are hot and same temp so coolant is flowing thru the core.. I would not put in acid, what you have done should have cleared the core and system. With the temps in the outlets I come back to a possible issue in the HVAC box or blend air door seal.

 

It very well could be clogged with casting sand from the block but I would assume flushing the heater core both ways would get rid of that ? Stumper for sure. Be careful with the muriatic acid it it's the good stuff along with the bad stuff,