Random overheating & weak interior heat issue - Heater core?

[03DodgeRamHemi]

New to the forum. I just bought an '03 Ram 1500 Hemi, 118,000 miles, and it had pretty weak heat inside since I've had it (about a week). Yesterday while driving I noticed the temperature gauge going up past half and the heat started blowing cold ONLY thru the driver side vents... Temp went back down and kinda fluctuated as I drove but stayed near normal. Still idles without trying to overheat. Was fine most of the day today but I noticed the temp gauge going up again on my way home tonight and the heat stopped blowing thru the drivers vents again, temp went back down as I drove. I read that the heater core could be clogged... Antifreeze looks fine and not low, doesn't overheat, runs strong, doesn't have any evidence of a head gasket blown. Any ideas??? Appreciate any feedback

 

[Ghostman]

My thought is 3 possibilities:
Bad water pump
Bad thermostat
or Heater core
Do a back flush on the heater core. Replace thermostat (cheap and easy), have water pump checked.

 

[Karlsweg]

Well on my 07 hemi , temp in middle of gauge is normal. Heat on half the side could be blend/ mode doors. I would start with the thermostat and make sure you “ burp” the system to get out the air first. And try rocking the fan side to side to see if the water pump has play in the bearing. They do like to go bad. If you find it is the heater core, I would replace all blend and mode doors heater core and a/c coil while in there.

 

[PolarisCobra]

Even with the heater core blocked completely, I don't think it would overheat. I would recheck level and look at water pump .

 

[Blackdodge2010]

Start with the thermostat. make sure to bleed it really well.