Hello everyone. I a, new to the forum and have a problem that has been giving me a really hard time.
I have a 2006 Liberty CRD with 250k Km (155k Miles). the problem started when the weather started getting cold (in Canada). I had a slow leak that was coming from under the passenger side foot area (leaking on the body by the firewall and coming down right under the foot rest of the passenger side). Even before this problem, I was not getting good heat when I put the fan on level 2,3 and 4 for about 30-40 minutes of driving. when the engine was reved, the heat came on and I get cold air when idling.
I did the thermostat, coolant reservoir, heater core and also flushed the system. the leak stopped. I also noticed that my viscous heater was not engaging at cold starts and not coming on at all. I bypassed the relay and put a switch in the car. I still have the same problem. I turn it on at cold starts and shut it off after about 15 minutes manually.
the previous owner did the head gasket and water pump last year (from ID parts) and I do get pressure in the tank after about 5 minutes of driving. I suspected that there is air in the system (even though I burped the system and added coolant to proper level) but I think after about 3 weeks of driving it would have been gone.
One weird symptom that I can hear is that when the engine is at operating temperature, after the car leaves a red light or a stop sign, I can hear coolant circulating in the heater core.
It does not overheat and also and I have pressure in the system.

If anyone has any clue of what the problem might be, I would really appreciate it.

Thank you all for your time

Sounds like you have a low flow issue through the heater core.
Make sure none of your heater hoses are pinched or have a kink in them that would restrict flow.
Might try disconnecting the heater core hoses (inlet & outlet) and do a reverse flush through it with a garden hose.
Pay close attention to how well the flow is coming out out the outlet pipe when water is applied in a normal flow direction.
If a restriction is believed to be in the viscous heater, you can bypass it with metal hose fitting available at most hardware or automotive stores.
Post what you find.

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Thank you for the quick response.
I checked the hoses going to the heater core, they were okay. I will bypass the viscous heater's hose and will update the progress.

Thanks again WW Diesel