1991 Cadillac heater not very hot update

[cadillac91]

1991 Cadillac:   I have found that when the temperature outside is 45 degrees or below the heater blows cold to somewhat luke warm.  Above 45 degrees the heater blows nice and warm consistently.  I changed the thermostat to 195 degrees back in December.  Also changes was the water pump and heater core.  Any thoughts?  You can email me at rkcrump@mtco.com

[TJ Hopland]

I would get one of those IR temp guns and check around to make sure the system is actually getting hot.   Lots of low quality t stats out there these days.  You can probe around the thermostat area and the hoses and compare temps.    When its luke warm see what the temp is on the hoses going into and out of the core, that will tell you if you have cool coolant or a control issue in the HVAC system.

How is the air flow?   I saw a lot of GM stuff (especially Cadillac) in that era where the AC coils seemed to have tiny leaks in them.  The leaks would leak a little oil which would then collect dirt and block the air flow.    All the air flows through the AC coil so if that gets blocked you don't get much flow.   The system controls if the compressor is on or off and then there is a door after the AC coil that controls how much (if any) air flows over the heater coil.    There is also a door that controls if the air is coming from outside or inside.