Hey guys, I have a '99 cherokee sport 4.0, and my heater blows cold. I changed my coolant about three months ago. The only time I have ever felt it warm is when my Jeep is running over 210, but that was in the middle of a SoCal summer going up to my house in Big Bear. Could it be my heater core being clogged up? Oh, plus the engine only has about 12,000 miles on it.

 

Either your heater core is clogged up or the blend door isn't working.

I'd start with back flushing the heater core. That takes 15 minutes and it's free.

 

I'd start by checking the blend door, takes 15 seconds, just saying.

 

I checked my blend door and it works. Then I flushed my heater core and a whole bunch of muddy water came out. Topped off and now I'm sweating bullets driving through the snow! Thanks for you help guys!!

 

I had the same problem and this is what came out when I flushed it.



And that's even diluted with clean water. The downfall of a previous owner's neglect and Stop-Leak. Heat works great now, but also developed a small leak in the heater core.

 

Could someone give me the down low on how to flush the heater core?

 

 

Had the same issue with my '99, and backflushing the heater core was the answer.