...Like the title says.

I've back-flushed other vehicles' heater cores in the past with noticeable heat improvement, ...just not my XJ. The hose end fit perfect over the larger end of the heater core, and put decent flow through it. I'm in the process of removing the HVAC box to replace the degraded door gaskets. I just didn't want to spill anti-freeze on the carpet. I was surprised how much crud there was. Probably replace the core anyway while I'm in there.

For other XJ owners here, back-flushing would be a good fall tune-up thing to consider.

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Well I had a heater core problem not to long ago.. Thing was though, it was just an A/C hose loose
The clamp was original to the vehicle so it lost its grip over the years and was letting the coolant drip down into the cab through that foam seal.
I had an extra clamp that was the exact same size and it was patched up in five minutes or less..
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00' Jeep Cherokee Sport// 4WD// 4.0L// Dana-35 axle//Custom Wrangler bumpers// Gadsden sticker
97' Dodge 3500//5.9L Hemi//Dually//Trusty Rusty// Dodge Transmissions are s***//Been sittin for 5 years

"The education of a man is never completed until he dies" -Robert E. Lee

Yes. Especially those models equipped with a heater control valve. The coolant mix stagnates in the core for half it's life.