I have a 2006 Pontiac Vibe. Same engine as the Toyota Matrix. The heat blows fine but isn't warm enough.
I checked the antifreeze and the level is fine and there are no leaks.
The hose into the heater core is hot. The out hose is fairly warm.
The heat is warmer when moving than when idling.
High is counter productive. The heat is only semi helpful when the blower is on low or just above.
I'm wondering what to do next?
Change the thermostat? The engine never overheats, seems to get up to temperature, but it took a long time to do it the other night when it was 8 degrees F.
Flush the heater core?
Backflush the heater core to clean it of debris and make sure that it has decent flow.
What are the next steps in troubleshooting this problem? What have I missed?